RHR: The Truth About Toxic Mercury in Fish ⏲ on OCTOBER 17, 2012 by CHRIS KRESSER 100 comments From a public health perspective, I think this is one of the most important shows I’ve ever recorded. As it is, most people do not eat enough cold-water, fatty fish, and this is especially true of pregnant women. Concern about mercury toxicity is one of the main reasons for this. But as you’ll learn in this episode, such concerns are unfounded and not supported by the science the majority of the time. In fact, we could go as far as saying it’s much safer to eat fish than it is to not eat it . DHA is a crucial nutrient for the development of the brain and nervous system, and has many other important properties. And as I’ve pointed out elsewhere , eating plant sources of omega-3 like flax or walnuts doesn’t cut it, because only a very small percentage (i.e. about one-half percent) of the short-chain omega-3 fats found in plants get converted into the beneficial long-chain omega-3 fat DHA. I know not everyone will have time to listen to the show or read the transcript, so here’s the 30,000 foot takeaway: mercury causes harm by damaging selenoenzymes in the body that protect against oxidative damage. As long as a fish contains more selenium than mercury (which the vast majority of both ocean fish do), and as long as background selenium intake is sufficient (which it is in most industrialized nations), then there is no reason to limit consumption of ocean fish. Please do listen to the interview with Dr. Ralston, an expert in mercury in fish and the protective effects of selenium, to learn more about this important subject. In this episode, we cover: 10:37 How did the idea that “eating fish is unsafe due to mercury” get started? 12:27 Why mercury in fish can cause problems 15:07 How selenium protects against the toxicity of mercury 18:12 Does it matter where selenium comes from in the diet? 20:25 The therapeutic dose of selenium that’s helpful in mercury toxicity 25:10 Why you need to know about the Selenium health benefit value (SE-HBV) 33:07 Is there any limit to how much fish a pregnant woman should eat? Like what you’re reading? Get FREE updates sent to your inbox. Your email I want to im CHRIS, I'M IN! ␡ Chris Kresser LET'S TAKE BACK YOUR HEALTH — Starting Now.
RHR: The Truth About Toxic Mercury inFish⏲ on OCTOBER 17, 2012 � by CHRIS KRESSER Ὂ� 100 comments
From a public health perspective, I think this is one of the mostimportant shows I’ve ever recorded. As it is, most people do not eatenough cold-water, fatty fish, and this is especially true of pregnantwomen. Concern about mercury toxicity is one of the main reasons forthis. But as you’ll learn in this episode, such concerns are unfoundedand not supported by the science the majority of the time. In fact, we
could go as far as saying it’s much safer to eat fish than it is
to not eat it. DHA is a crucial nutrient for the development of the
brain and nervous system, and has many other important properties.
And as I’ve pointed out elsewhere, eating plant sources of
omega-3 like flax or walnuts doesn’t cut it, because only a very small percentage (i.e. about one-halfpercent) of the short-chain omega-3 fats found in plants get converted into the beneficial long-chainomega-3 fat DHA.
I know not everyone will have time to listen to the show or read the transcript, so here’s the 30,000 foottakeaway: mercury causes harm by damaging selenoenzymes in the body that protect against oxidativedamage. As long as a fish contains more selenium than mercury (which the vast majority of both ocean fishdo), and as long as background selenium intake is sufficient (which it is in most industrialized nations), thenthere is no reason to limit consumption of ocean fish. Please do listen to the interview with Dr. Ralston, anexpert in mercury in fish and the protective effects of selenium, to learn more about this important subject.
In this episode, we cover:
10:37 How did the idea that “eating fish is unsafe due to mercury” get started?12:27 Why mercury in fish can cause problems15:07 How selenium protects against the toxicity of mercury18:12 Does it matter where selenium comes from in the diet?20:25 The therapeutic dose of selenium that’s helpful in mercury toxicity25:10 Why you need to know about the Selenium health benefit value (SE-HBV)33:07 Is there any limit to how much fish a pregnant woman should eat?
Like what you’re reading? Get FREE updatessent to your inbox. Your email I want to improve my...CHRIS, I'M IN!␡
Chris KresserLET'S TAKE BACK YOUR HEALTH — Starting Now.
35:15 The safety of freshwater fish39:10 Where the Suppversity article went wrong49:10 How to sustainably increase fish consumption
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Full Text Transcript:Steve Wright: Hey everyone, and welcome back to another episode of the Revolution Health Radio Show
brought to you by ChrisKresser.com. I’m your host, Steve Wright from SCDLifestyle.com, and
with me is integrative medical practitioner, licensed acupuncturist, and healthy skeptic, Chris Kresser. How’s the Bay Area, man?
Chris Kresser: Haha, it’s a little bit schizophrenic actually, Steve. We had the biggest heat wave we’vehad all summer about a week ago. It was like sweating-at-night type of heat, because we don’t have airconditioning out here. We don’t really need it usually. But there are a few days a year that I wish we did,and that was it! And then it’s been raining and sprinkling a little bit the past couple of days, so it’s a littlestrange. How are you doing?
Steve Wright: I gotta tell you, man, I’m a little sleep deprived. I haven’t been looking after my healthbecause my team, the Tigers, have been on the West Coast battling the Oakland A’s out there in Cali.
Chris Kresser: Haha.
Steve Wright: And I haven’t been able to turn it off, so I keep staying up all night long, trying to wait forthem to win, and luckily last night the man Verlander pulled it out for us, but it’s been a long week.
Chris Kresser: Haven’t you heard of TiVo, Steve? TiVo, video on demand, anything like that? You gottawatch it live, huh?
Steve Wright: Dude, with sports, I think you have to watch it live. Otherwise, you know, my phone, I’llhave to look in the morning to find out if they won. Yeah, everything else is totally recorded. I don’t watchcommercials anymore. I don’t do any of that stuff.
Chris Kresser: Yeah, right. Well, I’m doing all right with the sleep, but I’ve definitely been busy. I’mgetting ready to speak at the Weston A. Price Wise Traditions Conference in early November, which witheverything that’s been going on, I was like, Oh, man, this is not the right time to do this! But I’m actuallyreally excited about the talk. It’s on the gut-brain-skin axis, which is really fascinating, so I’ll be exploringthe connections between the gut and the brain, which we’ve talked about, of course, on the show before,and then the gut and the skin, which we’ve talked a little bit about on the show before as well. But thenthis kind of triangulation between the gut and the brain and the skin and how that plays out, and it turnsout that there are bidirectional connections in each cause. So the gut affects the skin, but inflammation in
the skin can actually trigger a stress response that will affect the brain, obviously, but also the gut. Andthen the gut and the brain have this bidirectional communication, which we’ve talked about whereinflammation in the gut can decrease activity in the frontal cortex, and that in turn reduces the output intothe pontomedullary area and the vagus nerve and causes more gut problems in this whole big, viciouscycle. And then stress can reduce stomach acid secretion and cause SIBO, which in turn causes intestinalpermeability, aka leaky gut, which causes local and systemic inflammation, which can cause or exacerbateskin conditions. So it’s this crazy system of feedback loops, and it’s a really hot topic in the scientificliterature, and I think it’s a kind of frontier for treating gut and brain and skin issues as looking at it as thisholistic piece instead of completely separate conditions.
Steve Wright: Well, that sounds like a spiderweb of amazingness for me because I’m a big nerd on thatstuff too, so I cannot wait to see that talk.
Chris Kresser: Are you coming?
Steve Wright: Hopefully, hopefully.
Chris Kresser: Cool.
Steve Wright: We’re doing a lot of changes on our site as well, so it’s been kinda busy and just trying tomake sure that we can make it out there and get the stuff that we’re doing done as well.
Chris Kresser: Yeah. Well, I hope to see you guys there. One thing I’m excited about is it’s like a 40-minute drive from my house, so I don’t have to do any big travel at least.
Steve Wright: Oh, very nice, very nice. Well, I know that you’ve done a skin series and obviously we’vetalked a lot about gut-brain on the blog, so hopefully after this you can maybe distill some of the bestpoints down and put them on the blog for the people who won’t be able to make it, because I don’t thinkthat’s a free conference online, right? People have to buy that?
Chris Kresser: That’s right. They sell the DVDs afterward. So yeah, we’ll definitely do a cliffsnotes versionor something on the show. Maybe it’d be good. We can talk a little bit about it in November or Decemberor something.
Steve Wright: All right, cool. Well, without further ado, we have a very special guest on the show today. Chris, do you want to tell us a little bit about him?
Chris Kresser: Sure. Yeah, I’m really excited. I’m so grateful that he accepted our invitation. His name isDr. Nicholas Ralston. And I first became aware of his work back when I wrote the special report on
essential fatty acids and an article that I think a lot of people have read by now called Is it safe to eat
fish? A lot safer than not eating fish! And the gist of the article was that the concerns that a
lot of people have about mercury in fish turn out to be unwarranted in most cases and that, in reality, thebenefit of eating fish, all the beneficial nutrients like the long-chain omega-3 fats and selenium and other
nutrients, far outweigh any potential risks because selenium can protect against the adverse effects ofmercury toxicity. And in doing research for this, I came across Dr. Ralston’s work because he’s one of themost prominent researchers in the field and has a really extensive background in this area, and he’s reallythe perfect person to have on the show to discuss this. And I wanted to do it now because there’s been
some chatter in the paleo blogosphere lately about an article that appeared on a blog called
SuppVersity. And I don’t remember the exact title of the article, but we can post it in the show notes.
But the gist of that article was that contrary to what some people like me have said recently, that seleniumdoesn’t actually protect against the adverse effects of mercury. So I wanted to have Dr. Ralston on to talkabout the general issue of selenium and mercury, and mercury in fish, and then specifically address someof the things in that article and point out where that analysis was lacking. So I’m really honored to have Dr.Ralston on the show and can’t wait.
Steve Wright: I’m extremely excited as well because I think this is a topic near and dear to everyone in thereal food community, so I can’t wait to hear what he has to say.
Chris Kresser: Let’s do it!
Steve Wright: OK, Chris, before we talk to Dr. Ralston, why don’t you grab some water, get your notesprepped, and I’m gonna tell everyone about Beyond Paleo. If you’re new to our show, or you’re new tothe blog, or you’re new to paleo, you’re probably gonna want to check out a free 13-part email series thatChris has put together that includes his top tips and tricks for burning fat, boosting energy, and preventingand reversing disease without drugs. Now, over 20,000 people have already signed up to get this, soneedless to say, if you’re listening to this and you haven’t read it, it’s something that’s in demand and
you’re probably gonna learn a lot from it. So if you’re interested, head over to ChrisKresser.com,
look for the big red box, and go ahead and put your name and email in that box, and Chris will startsending you those emails over the next few weeks.
OK, Chris, how are you doing? You ready?
Chris Kresser: Let’s do it. Dr. Nicholas Ralston is a research scientist at the University of North DakotaEnergy and Environmental Research Center, EERC, involved in evaluating potential human health effectsand risks resulting from environmental exposure to air toxics. He received his PhD in biomedical researchbiochemistry from Mayo Medical Center and his bachelor’s of science in biology from Mayville StateUniversity. Dr. Ralston’s principal areas of expertise include the biochemistry and analytical approaches toquantitative assessment of immune research and inflammation at the molecular and cellular level. Hisprimary interests are in trace element physiology and the pathophysiology of toxic trace elementexposures as well as prevention, protection, and remediation strategies. His current research interestsinclude examinations of the molecular mechanism of methylmercury toxicity, selenium-dependentbiochemical processes involved in preventing the neurotoxic effects of mercury, both of which we’ll bediscussing on the show, mechanisms of pulmonary particulate pathologies, mercury phytoremediation, andother means of diminishing bioaccumulation of mercury in fish.
Prior to his position at the EERC, Dr. Ralston worked at Grand Forks Human Nutrition Research Center andBowman Gray Medical School at Wake Forest University. He has authored or coauthored over 50
professional publications, research articles, and book chapters and given numerous invited presentationson health issues related to methylmercury-dependent inhibition of brain selenoenzymes and beneficialeffects of maternal seafood consumption on child development outcomes.
I first became aware of Dr. Ralston’s work back when I was writing a series on the importance of long-chainomega-3 fatty acids and I was doing some research on the idea that we should avoid fish consumptionbecause of mercury toxicity. And I came across some papers Dr. Ralston had written, and they reallychanged my view on this issue, and I wrote an article about that. And since then there’s been a lot ofdiscussion of it and some further articles written in the paleo blogosphere, shall we say, that have beencritical of the idea that selenium protects against mercury toxicity. So I invited Dr. Ralston to come on theshow and discuss this. I couldn’t think of a better person with more expertise to help us shed light on thisissue and clear it up once and for all, so welcome to the show, Dr. Ralston.
Dr. Nicholas Ralston: Well, thank you very much, Chris. Happy to be with you.
How did the idea that “eating fish is unsafe due tomercury” get started?Chris Kresser: So let’s start with how the idea that eating fish is unsafe due to mercury got started in thefirst place.
Dr. Nicholas Ralston: Well, it’s kind of been understood since the time of the Romans and even the earlyChinese that mercury is a toxin, so in the late ’50s there were findings that a bay in Japan where mercuryhad been released from a plastic-producing chemical plant. Large amounts of mercury were beingreleased, and this mercury was being accumulated in the fish. The fish had huge amounts of mercury inthem. They were extraordinarily toxic and were lethal to the animal life that was eating it such as cats thatwould eat the fish that were washing up on shore from being killed by the mercury. People that werecatching fish from that small bay were getting huge doses of mercury, and at that time that was first thatscientists recognized that unborn children were particularly sensitive to the effects of mercury becausewomen that weren’t showing any bad effects — Many people were showing severe effects, but evenwomen that were not showing bad effects would have children that were just tremendously harmed by theamount of mercury they were exposed to. So since that time, there have been a lot of human studies, butthat was really the start of it all. It was called Minamata Bay.
Why mercury in fish can cause problemsChris Kresser: Right, the Minamata — I’ve seen some pictures from that tragedy and they’re pretty horrific,so I could definitely see how that would scare people, especially mothers who are thinking about whetherto eat fish during pregnancy. So how does mercury in fish and in general cause problems? I want to askyou this question particularly because I think there’s some misunderstanding out there about how mercurycauses problems. So can you clear that up for us?
Dr. Nicholas Ralston: Yeah, actually it’s kind of easy to understand why this misconception has gottenaround. It kind of comes down to simple problems that confuse people. Like, some people don’t reallyseem to understand that whales and fish are not the same, that they’re totally different as far as theirphysiology. And some people don’t recognize that ocean fish and freshwater fish are not the same, and
you know, they’re certainly not. The same thing about mercury exposures: It seems like many peoplethink that how you get exposed to mercury doesn’t matter and all you need to know is how much mercuryyou got exposed to, but that’s really not the case. We’re seeing that exposures to mercury that are acertain level that are known to cause harm in one population, higher levels of exposure are having noeffects at all in other populations. The things that we’re finding out, however, are those early studieswhere there were harmful effects seen, they all involved consumption of pilot whale meats. Pilot whalesare predatory whales that eat a lot of — They’re the top predators of the ocean, so they get a lot ofmercury in their meat. They can have twice as much mercury in their muscle meat than selenium, whichreally makes them almost unique. A second exception is shark meat. Shark meats are the only type of fishthat we’re aware of where there are consistently high levels of mercury relative to selenium. Almost allother types of fish have more selenium than mercury, so that’s the important crux of the matter. We seeharm whenever people are exposed to a lot of mercury when it’s mercury in excess of selenium, butpeople that are exposed to even more mercury than was seen in those studies but in the presence ofplenty of selenium, like most ocean fish and even most freshwater fish have, we’re not seeing thoseadverse effects. So it’s kind of easy for me to understand why people get confused about this, but wehope to clear up the confusion as time goes on.
How selenium protects against the toxicity ofmercuryChris Kresser: Great. So let’s kind of zero in on a more molecular level and talk a little bit about howmercury exactly causes problems, because I think there’s maybe some misunderstanding about this aswell. The idea, for example, that mercury has a primarily harmful effect by causing oxidative damage. Isthat really how it works?
Dr. Nicholas Ralston: Well, it is true that in animals or humans that are exposed to huge amounts ofmercury, oxidative damage is the primary thing that we see, but the reason for the oxidative damage hasbeen misunderstood. Certain elements, like if you have iron toxicity or if you have too much copperexposure, you’ll get oxidative damage because direct reactions between this excess amount of iron orcopper in your tissues causes oxidative damage to lipids. But in the case of mercury, that doesn’t happen. You can have a lot of mercury in the presence of lipids and no direct damage occurs. What it’s really allcoming down to is that tissues that have a lot of oxygen consumption, like brain or heart, they produce alot of free radicals or oxidative molecules, and so you need a real potent antioxidant system to keep thoseoxidative molecules from harming your brain lipids or your heart lipids, and if you don’t have thoseenzymes doing their job, you will start accumulating damage rapidly.
Now, the thing that’s crucial about the whole issue is that selenium-dependent enzymes are probably themost functionally elite enzymes there are for preventing oxidative damage. Without selenium-dependentenzymes, vitamin C can’t perform its function. It would do its job once and then it would be useless. Ittakes a selenoenzyme to make vitamin C able to do its job again and again and again so it’s always able toprotect. The same thing with several of the other very important antioxidant molecules that we allrecognize are huge in protection against oxidative damage. So without selenoenzymes, oxidativedamage is going to be happening fast and furious. The only thing that we know of that can killselenoenzyme activities is mercury. Mercury specifically binds selenium-dependent enzymes. Mercuryhas a million-times higher affinity for selenium than it does for sulfur, its second best binding partner.
Dr. Nicholas Ralston: So you get too much mercury and it’s going to find and bind your selenium, andyou’ll pretty quickly lose your selenoenzymes. But if you’re taking in a lot more selenium than you aremercury, well, you will have mercury taking out enzymes, but as soon as they’re being taken out, moreselenium-dependent enzymes are being made. So we don’t see toxic effects when there’s food that hasmore selenium than mercury being consumed.
Does it matter where selenium comes from in thediet?Chris Kresser: OK, yeah, that’s very clear. So this is a question I’ve been asked a few times: Does itmatter where the selenium is coming from in the diet? So, for example, does the selenium have to be inthe food that contains the mercury, or is it more just the background selenium intake from all sources inthe diet that matters most?
Dr. Nicholas Ralston: Well, let’s just talk ocean fish for a moment. They’re very, very rich in selenium, so ifyou’re wanting protection against mercury exposure, like if you happen to be eating a lot of whale meat,the one study that was done that found severe effects from mercury exposure, the moms were eating pilotwhale meat and so 95% of their mercury exposure came from eating the whale meat. And of course, sincethat whale meat contained four or five times more mercury than selenium, it they’d only been eating thatwhale meat, those moms would’ve been in a lot of trouble, and their babies would’ve been severelyharmed.
Chris Kresser: Right.
Dr. Nicholas Ralston: But fortunately those folks were also eating a lot of ocean fish, so the ocean fishprovided the selenium that protected against the mercury from the whale meat. Most people, whenthey’re concerned about mercury exposure, it’s actually from eating fish, but very few people in the UnitedStates eat whale meat, of course, so in most cases, unless somebody was eating a lot of shark orhappened to be eating maybe freshwater fish from a lake that did happen to have more mercury thanselenium — That occurs in very few places, but we’re fairly sure it’s occurring in places that need to belooked at more carefully. If that is happening, selenium from other sources — Fortunately, Americans,everything we eat tends to be rich in selenium, so if you’re eating a healthy diet, you’re getting a goodamount of selenium. But if you do happen to be eating some foods that have more mercury thanselenium, such as shark meat, pilot whale meat, or maybe a freshwater fish that has more mercury thanselenium, any other source of selenium will be protective, but it’s probably best to simply avoid the foodsthat have such high mercury relative to selenium.
Chris Kresser: Right. So let’s say someone has mercury toxicity, perhaps not from eating pilot whale meatbut from another source. Is there a therapeutic dose of selenium that would be helpful in thatcircumstance? My understanding is, of course, that like most nutrients there’s a U-shaped curve forselenium. There’s a sweet spot. Too little is not good, but too much is not good either because ofselenosis.
The therapeutic dose of selenium that’s helpful inmercury toxicityDr. Nicholas Ralston: Absolutely right. Generally in nutrition we figure that anything over 1 mg per day,1000 mcg — that’s the same as 1 mg — is too much. And really we prefer people to stay below thatconsiderably; 200 mcg per day is kind of a typical supplemental dose. Not too many people in the UnitedStates absolutely need it. Well, certainly they’re not going to be deficient, but there are some healthbenefits that are supposedly associated with supplemental levels of selenium such as anticancer effects ofit have been reported occasionally.
Chris Kresser: Right.
Dr. Nicholas Ralston: So 200 mcg is a plenty safe dose, but really if you’re eating normal foods andespecially if you happen to be consuming plenty of seafoods, you’re getting a healthy amount of seleniumin your diet anyhow. Most people get about 50 mcg per day, so an additional 200 mcg is taking it upabout another couple hundred percent, so it’s a reasonable thing to do if people were concerned. Forinstance, I’m working in a study in Peru where people are working in gold mining operations where theydo a lot of mercury release into their environment. It’s something that really would be good if they wouldstop doing it, but since they can’t be dissuaded at this time, there’s going to be intervention trying to gettheir selenium levels up to try and protect them and their children that happen to be living in the area withthem protected against the mercury to a greater extent.
Chris Kresser: Right.
Dr. Nicholas Ralston: But as always, the best thing is to avoid the mercury exposure, and the fortunatething is in the United States we generally have such rich selenium intakes that for the most part, unlesssomebody was exposed to really unique cases of either industrial exposures to mercury or something likethat, most of the time the concerns are not going to be too great. This is not the case in other countrieswhere selenium is poorly available and in some cases mercury exposures might be much greater. Soelsewhere in the world, there’s actually far greater concern than in the US.
Chris Kresser: Do you have an opinion, Dr. Ralston, on the form of selenium that people should take ifthey choose to supplement with it? For example, I have some patients that are allergic to seafood, so themain source of selenium that they would get in the diet isn’t available to them. And there’s, of course,selenomethionine, selenite, methylselenocysteine, and all these different forms and a lot of controversyover which form is the most beneficial to supplement with.
Dr. Nicholas Ralston: Well, yeah, the selenomethionine is one of the major forms that is produced inplants. Actually a lot of people will be taking selenized yeast, and what they do there is they provideselenium to yeast while they’re growing, and the yeast will take up the selenium and form typical biologicalmolecules that are a good source of selenium. Too much selenomethionine has been associated withsome problems, so like you were saying, too much is not good either, but pretty much this is the case witheverything now. If you take five times the healthy dose of water, that’s lethal.
Dr. Nicholas Ralston: With selenium it’s the same way; 200 mcg is no problem, but once you get morethan five times that, you’re starting to get into trouble. But most people are down around 50 mcg, sonobody ever gets close to 1000 mcg per day, but there simply is nothing in the world that I’m aware ofwhere there is not gonna be a risk associated with having too much of it, everything from water to oxygen. Oxygen, everybody on the planet eventually dies from oxygen toxicity. We need to have the oxygen forsupporting life processes, but we all die eventually of oxidative damage, and so oxygen is probably themost lethal element on the periodic table. And the best protection against oxidative damage is healthyamounts of selenium. Too much, not a good thing, but that’s true of everything.
Why you need to know about the Selenium healthbenefit value (SE-HBV)Chris Kresser: OK, so we’ve discussed the fact that fish that have more selenium than mercury arebeneficial because selenium protects against mercury toxicity, so tell us a little more about this Selenium —Is it the Health Benefit Value? The Se-HBV?
Dr. Nicholas Ralston: Yeah, the Health Benefit Value. Because no consumer and very few regulatoryscientists would like to try and have to figure out, OK, it’s got this much mercury, this much selenium, so isit a good fish or is it a bad fish? We created the Selenium Health Benefit Value as a simple, straightforwardway that a consumer could know that the fish that they’re eating is actually beneficial and at least as far asmercury-to-selenium relationships, how beneficial it is. So if it have more mercury than selenium, such asthe pilot whale or the shark species that I was mentioning that have been found to be harmful, it has anegative Selenium Health Benefit Value, because any food that has more mercury than selenium,consuming that is not going to be good for you. Like, for instance, the pilot whale meats had a negativevalue of -80, so eating that was a fairly extraordinarily bad food for a mom to be eating.
Chris Kresser: Right.
Dr. Nicholas Ralston: But fortunately the ocean fish that the moms were eating plenty of had values thatwere around 50 to 100 positive, so they more or less balanced out almost entirely. There was still anegative effect, but without the seafood consumption, without those moms eating those ocean fish thathad a small amount of mercury, so you would’ve thought that it would’ve made the mercury exposureeffects worse, completely did not. Instead of making it at all any worse, it completely protected or nearlycompletely protected, so the children only had subtle neurodevelopmental effects. It was actually lessthan an entire IQ point in the worst cases with the children of the moms that were eating the most whalemeat and the least ocean fish, so it still was — You know, nobody wants to lose even a part of an IQ point,so it’s definitely advisable to avoid eating whale meat. And in the Faroe Islands — It’s a protectorate ofDenmark that’s between Scotland and Iceland. It’s an island group where the people are mostly Danishheritage — They were eating lots of whale meat during pregnancy, and now they’re being advised duringpregnancy especially don’t eat whale meat, but certainly go ahead and eat as much fish as you canbecause we’re finding that eating ocean fish, we’re getting IQ benefits instead of harms.
Chris Kresser: So, was that the only study that ever showed harm from eating mercury in fish, Dr. Ralston?
Dr. Nicholas Ralston: No. The Faroe study is probably the one that’s most often cited because the
statistics on it were done well and it was a good-sized study. The drawbacks are that the exposure wascoming from pilot whale meat instead of ocean fish. But before that study, there was a study done in NewZealand, where mothers that were eating fish and chips were getting exposed to fair amounts of mercury,but it’s important to note that the fish that they were using to make fish and chips, for some reason theywere using large shark meats, which nobody would do that now, but back in that time, apparently theywere catching shark and it seemed like it was usable for that purpose. So in New Zealand, they weregetting exposed to shark meat that had high mercury relative to selenium, and the New Zealanders, unlikeAmericans, New Zealand was one of the most selenium-deficient nations on earth at that time. Soexposure to mercury in New Zealand, they had very little chance to be able to have other dietary sourcesof selenium to make up for the losses from eating those shark meat filets, so they were in a lot of trouble. So those are two of the big studies that have shown adverse effects, but now we’ve had a lot morestudies, huge studies with many thousands of women that are eating ocean fish, and we’ve been followingthe children since the time prior to birth to the time — I think now those children in some of the biggerstudies are almost 20 years old.
Chris Kresser: Wow.
Dr. Nicholas Ralston: And the more fish that the mothers ate in those studies, these very appropriatelydesigned studies — The one I’m referring to was done in England, so you know, very much like what thecase is in the United States, the type of foods they eat are generally seafoods. Maybe they eat a little bitmore fish and chips than we do in the US but still eat a lot of fish. They find that the benefits of eatingocean fish during pregnancy amount to as much as three to five IQ points of benefit. So moms that areavoiding eating ocean fish because of the harms that are associated with eating whale meat are missingout on the benefits that actually are accompanying eating ocean fish.
Chris Kresser: So we really need to turn this idea around where not eating fish during pregnancy is whatmight be considered unsafe rather than eating fish, provided the fish has less mercury than selenium, orcourse.
Dr. Nicholas Ralston: Yeah, exactly. And just about all varieties that are typically sold as commercialtypes of fish are fine. Even some sharks are fine. It’s just certain of the very, very predatory types likemako shark is one that we included in one of our big studies recently. Mako shark consistently has moremercury than selenium, so a pregnant woman or a woman that might become pregnant should avoideating mako shark. Many swordfish can have almost as much mercury as selenium, so perhaps swordfishshould be avoided, too. And of course, shark and swordfish are two of the types of fish that women arealready advised by FDA and EPA to stay away from. And the other two types are also high in mercuryrelative to selenium; tilefish and king mackerel are foods that definitely need to be avoided duringpregnancy. Men that are not likely to become pregnant don’t have to worry about eating shark orswordfish because really it is that sensitivity of the unborn fetus. When you’re developing a new brain, youcannot have a shortfall of selenium at any time. A newborn brain is making 50,000 new brain cells persecond, so you don’t want to have even a few seconds of too much mercury relative to selenium.
Chris Kresser: Right.
Dr. Nicholas Ralston: So the more ocean fish moms eat during pregnancy, though, the more selenium,omega-3 fatty acids, vitamin D, and other nutrients that are known to be hugely important for developing
healthy brains as well as contributing to the health of the mom during pregnancy and the post pregnancy. Eating more fish is actually good advice for women, but unfortunately still too many people have themisconceptions that are kind of the outdated ideas, and we’re trying hard to get everybody on board sothat they understand this and have a unified message so more and more of the people that formerly werearguing, Oh no, fish has to be avoided, are coming around and saying, Oh, no, actually ocean fish need tobe eaten in greater amounts.
Is there any limit to how much fish a pregnantwoman should eat?Chris Kresser: Right. So is there any limit then to how much fish a pregnant woman should eat,presuming she’s eating the forms that are positive on the Selenium Health Benefit Value Scale?
Dr. Nicholas Ralston: Well, in nutrition, it’s usually a good idea to not focus too much of your diet in anyone area. Variety is good in many ways, and twice a week would certainly be a — I think that’s what thelevel was that was associated with the benefits in the British study. Certainly in Japan they probably eatocean fish more often than that, and certainly from the effects we see among the Japanese, it looks likethey’re beneficial. In Japan, however, they do have to be cautious because in some parts of Japan they doeat porpoise meat, whale meat, and some of the types that are not safe. But in the US, commerciallyavailable, the store-shelf-type fish almost always are going to be the beneficial ones rather than theadverse ones.
Chris Kresser: Right.
Dr. Nicholas Ralston: So, a couple meals a week would be a good idea. I’m not sure if I’d be in favor ofwomen eating fish three meals a day, seven days a week.
Chris Kresser: Right. But something above 12 ounces and not going crazy with it. A moderate amountthere, yeah. And we’re kinda far from that now. I think the last statistics I saw, according to the NationalFisheries Institute, Americans consume only 5 ounces a week of fish high in long-chain omega-3, which isless than half the recommended amount. And I think they also estimated that almost 15% of women ofchildbearing age eat no fish at all, which was somewhat alarming.
Dr. Nicholas Ralston: And a lot of that’s because they’re concerned. They’re heard that eating sometypes of seafood is bad for you, so they just want to avoid seafood entirely. But they didn’t realize theseafood that was being mentioned was whale meat.
Chris Kresser: Right.
Dr. Nicholas Ralston: And while, yeah, that is a seafood, when I think of seafood I’m never thinking whalemeat.
Dr. Nicholas Ralston: Most Americans are not thinking whale meat.
The safety of freshwater fishChris Kresser: That’s definitely accurate. So what about freshwater fish? I get a lot of questions aboutthis. We’ve seen a lot of information about the Selenium Health Benefit Value of ocean fish, but arefreshwater fish safe, too?
Dr. Nicholas Ralston: Yeah, in general, more than 98% of the lakes that we have included in our study —We’re doing an EPA-funded study of lakes from all across North America, and in more than 98% of theplaces that we have data for, we’re seeing that the selenium is in excess of the mercury, so those fish arefine. In some of the places where the mercury is approaching equal amounts with the mercury, therewe’re actually thinking that further study is needed. We need to perhaps rather than warning about the98% that don’t appear to be problems, we should focus our efforts on the 2% where problems mightoccur. And the problem is that right now people see, well, it’s got this amount of mercury and it’s the sameas mercury everywhere else, while the problems is everywhere else it’s not causing problems becausethere is plenty of selenium there.
Chris Kresser: Right.
Dr. Nicholas Ralston: If you’re happening to eat fish from the 2% of the lakes where the mercury is inexcess of the selenium, well, then there could be potential problems. And it’s completed becausewherever selenium is poorly available, and although in general the United States and most of NorthAmerica is rich in selenium, there are places where there is too little. And wherever there’s too littleselenium, the thing we’re finding that’s happening very consistently across North America is where there’sless selenium available in the environment, there’s more mercury accumulating in the fish. So that’s one ofthe reasons why I think this is an area of special concern. We don’t want to have mercury accumulation inany of the fish but especially not happening in fish where there’s too little selenium to begin with.
Chris Kresser: Is that lower selenium due to depletion in the soil or different dietary patterns in thoseregions or both, or do we know?
Dr. Nicholas Ralston: Well, fortunately in the US we have mostly a centralized food distribution system, soeven if you’re living on the West or East Coast, you’re probably eating bread products that may have comefrom, like, the heartland of the nation where selenium tends to be rich in the soils. But on both coaststhere’s a greater abundance of igneous soil, soil from breakdown of igneous rock. And around volcanoesthere’s a very bad smell. That’s because sulfur and selenium both volatilize out of rock, and both of themsmell very bad. But that rock that’s left behind from volcanic activity is very low in selenium. Sosedimentary rocks in general are the opposite; they’re rich in selenium. So if you happen to live in a part ofthe nation where there’s a lot of igneous rock or if you’re in Florida where the rock material is from coralthat has been washed so any selenium that was there has been washed so much so that there’s noselenium left in the soil, that’s two conditions that are just primarily geological. The other situation is ifthere’s low pH, and of course, with acid rain deposition that we used to have very severe in many parts ofthe nation, having low pH has a very bad effect on selenium. Even if the selenium is in the soil, if acid rainis lowering the pH of the soil and water, the selenium will not be available, and so mercury accumulation inthe fish will be greater.
Where the Suppversity article went wrongChris Kresser: So, Dr. Ralston, a couple weeks ago, I sent you an article on the SuppVersity
website that claimed that mercury in fish is harmful regardless of selenium content, and they cited an
animal study, a mouse study, I believe, and then also a human study that I think took place in Finland. Andyou were kind enough to look into that and get back to me on some shortcomings of that analysis. Canyou talk a little bit about that?
Dr. Nicholas Ralston: Yeah. In the first study, one of the misconceptions that people have about themercury-selenium interaction is that it’s all about selenium somehow or another binding the mercury andkeeping mercury from causing harm. So they have heard that mercury and selenium have this highbinding affinity, but they’re imagining that mercury is causing harm in the body until selenium binds it. And,well, that’s not at all the case, that’s kind of the flipside of what’s really going on. It’s not that seleniumbinds mercury and keeps it from causing harm. It’s that when there’s too much mercury, that binds all yourbody’s selenium and keeps your body’s selenium from doing good. And so if too much mercury is present,knocks out your enzymes, you have no more protection against oxidative damage, losing all of thoseenzymes that nothing else can wipe out, damage will definitely happen if you have a lot of mercury comingin and not enough selenium to keep those enzymes going. And so the first study, they said they werecomparing the effects of selenium, but remember the negative Selenium Health Benefit Value of pilotwhale meat that I mentioned?
Chris Kresser: Yes.
Dr. Nicholas Ralston: That was a value of -80. The two diets that they compared in the animal study,unfortunately they didn’t understand really the molar relationship. Both of the diets were below 100, a -100Selenium Health Benefit Value.
Chris Kresser: Oh, wow. I see.
Dr. Nicholas Ralston: So they were comparing a -100 to a -160, and they found out, Oh, my goodness! Both of them are bad for you! And it’s like, well, yeah, if you’d calculated out the Selenium Health BenefitValue, you would’ve said, yeah, both of these should be bad for the animals. So their study actually provesthat when you have more mercury than selenium it’s bad for you, and we all kind of agree on thatcompletely.
Chris Kresser: Haha, right.
Dr. Nicholas Ralston: So it’s not that they were wrong. They actually did a good study, but they didn’thave a control that included a diet that had a positive Selenium Health Benefit Value. Because youcertainly can have even a lower selenium — It could still be negative and not as bad. So, like a -10 mightnot be anywhere near as severe as a -100. But once you’re severe, a -100 is pretty severe, and -160, well,you’re comparing severe to slightly more severe. So it’s a study that’s a good start, and you know, what Ireally should do is contact the authors and suggest in their next study that they take into account the molarrelationship a little bit more carefully and compare Selenium Health Benefit Value diets that includepositive Selenium Health Benefit Values such as ocean fish provide. Most ocean fish have values of 200
Dr. Nicholas Ralston: The types of fish that were consumed in the Faroes, I think they were between 50and 100. But many of the types of fish that people think are worrisome, like various types of tuna. Forsome reason, tuna gets focused in on a lot, but almost all of the tuna that I have looked at have had valuesof around 200 positive. So rather than being adverse, the more tuna that’s consumed, yes, you are gettingexposed to some mercury, but you’re getting 20 seleniums for every mercury, so the worst damage youcan have is one mercury takes one selenium, so you’re still 19 to the good. So it’s just a small matter of justkeeping track more carefully of how much mercury relative to selenium.
The second study that was mentioned in the website was from Finland, and eastern Finland is anothernation just like New Zealand that has extraordinarily selenium-deficient soils. In fact, Finland is the onlynation on earth that has every place in Finland the fertilizers that farmers put on their fields have to haveselenium added, so that’s helping the people in Finland get a little bit less selenium deficient. But thestudy is being done in eastern Finland, which is sort of a woodland and lake district. It’s kind of like theMinnesota of Finland. So not as many farm fields in this lake country, so there’s not selenium getting intothose lakes, so what they have is very high levels of mercury in the fish, very low levels of selenium, sothey’re taking in a worst case scenario-type of fish. And just like I mentioned, brain and heart both havehigh rates of oxygen consumption, so they need a lot of protection against oxidative damage or you’regoing to start showing all of these damages throughout the body, but particularly the brain and heart.
So in that study done in eastern Finland, they were eating freshwater fish, and like I mentioned before,wherever selenium is poor, mercury accumulation is going to be accentuated, and that was definitely thecase there. They weren’t eating ocean fish. That’s the thing I was pointing out at the start. Too manypeople think freshwater, ocean fish, no difference. That’s not at all true. Freshwater fish can vary inselenium a lot, and they can have a lot of mercury relative to selenium or a lot of selenium relative tomercury, so a lot of variability in freshwater fish. Ocean fish are very consistent. If it’s a type like a shark,it’ll consistently — if it’s like a mako shark, it’ll consistently have a lot more mercury than selenium. And ofcourse, it gets worse as the fish gets older. An older shark will have more, but even the younger sharkshave a lot of mercury relative to selenium. Freshwater fish, if the people in Finland that were eating all ofthe freshwater fish had instead been getting some ocean fish along with their freshwater fish, we wouldprobably see some beneficial protective effects, but as that study showed, the high mercury exposure thatthose people were getting from eating these high-mercury freshwater fish was accentuating their cardiacdisease risk — I think it was their risk of sudden cardiac death — by 50%, which is a fairly significantincrease. But that’s in a population where freshwater fish with high mercury relative to selenium are beingconsumed.
And another thing that study found was that omega-3 was not as important in protection as the mercurywas in causing harm. So one of the things that we’re looking into more and more right now is that maybethe benefits of eating ocean fish, certainly the omega-3’s are important, but to protect the omega-3’s fromoxidative damage — They’re very vulnerable to oxidative damage. In fact, when we’re talking oxidativedamage, that’s one of the types of molecules that is an easy target for an oxidative molecule to harm. Destroying lipid layers on a nerve cell is going to be very harmful for signal transduction. Terrible thingshappen when too much oxidative damage occurs. But if you have selenium-dependent enzymes that are
able to protect them against oxidative damage and there’s another type of selenium-dependent enzyme —There’s actually 30 different types of selenoenzymes in humans. Another type of selenoenzyme takesfatty acids that have already been damaged and fixes them.
Chris Kresser: Wow.
Dr. Nicholas Ralston: Undoes the oxidative damage to them. And selenium-dependent enzymes are alsoresponsible for undoing a certain type of oxidative damage that occurs to proteins. So without selenium-dependent enzymes that prevent and reverse oxidative damage, certainly seeing the adverse effects inthe Faroes and in New Zealand and in Finland, in each of those cases, those adverse effects agreecompletely with what we would expect to see. And conversely, in the areas where selenium-rich oceanfish are being consumed, the beneficial effects that are being seen completely agree with what we’dexpect. So the Selenium Health Benefit Value does predict the adverse effects where they’re being seenand the positive effects where they’re being seen. And so far as we’re currently aware, this is the onlyseafood safety criterion that is able to predict both benefits and risks.
Chris Kresser: That’s fascinating. I wasn’t aware of that. So in addition to helping prevent mercurytoxicity, it prevents oxidative damage of the long-chain omega-3 fats, and that’s yet another reason tochoose fish that have more selenium than mercury.
Dr. Nicholas Ralston: Yeah. The body is actually pretty capable, though. If you’re taking in a low-selenium diet, the body will hang onto all the selenium it’s got, and it’ll take a long time for you to getdeficient. But taking in more is always good. The body doesn’t mind getting rid of extra selenium, but ifyou’re taking in too little, well, it’s hard to find extra selenium if there’s not any in your diet.
How to sustainably increase fish consumptionChris Kresser: Right. So one last question, and then I want to pick your brain a little bit about someadditional resources for folks about this stuff. I think you’ve done a great job of making it clear why weshould be eating more fish in general and particularly pregnant women and perhaps kids than the ratessuggest that people are eating them now. What about ecological considerations of increasing fish intakeon a population-wide basis? This is a concern of mine or at least something that I pay attention to, and I’mwondering if you have any thoughts on how we can safely increase fish consumption without destroyingfish stocks even further.
Dr. Nicholas Ralston: Yeah, sustainability is a major issue, and so if we did start having all of the women inthis country start eating more fish, it could be a bit of a challenge because it’s certainly not an unlimitedsupply of ocean fish out there. Other nations are taking quite a bit more ocean fish than perhaps the USfleets are, and the US fleets are very cautious and careful for various things that we mandate must not becaught, for instance, protecting sea turtles, dolphins, things of that nature, so American fishing fleets arevery careful not to, or try as hard as they can not to catch either sea turtles or porpoises or any of the otherspecies that we do want to protect, but not all fleets from around the world are being as cautious asAmerican fleets. So the fishing haul-in from the oceans, many nations are taking in a lot more and causingharm to turtles and porpoises, etc., around the world. So we’ve got a problem that American fleets are nottaking in as many relative to our population as perhaps some of the other nations. It has to be sort of aworldwide agreement that certain types of species have to be protected, the sustainability of the fish that
are present. I mean, if you look at the world, they’re all connected, so it’s essentially almost one ocean. Having too many fish collected in one area means less that can be collected in the other areas, so I thinkthere’s got to be increased international agreement about how to properly take care of the world’s oceans.
Chris Kresser: Um-hum. I’ve read a few interesting things about some improvements in aquaculture andcertain species like barramundi that have a favorable fatty acid profile and seem to do pretty well inaquaculture environments, so I wonder if that can make a contribution as well.
Dr. Nicholas Ralston: Yeah, aquaculture is catching on pretty much worldwide. In the US, there isincreasing aquaculture, but we’re actually kind of slow off the starting block with aquaculture. We have theopportunity to diminish the transportation costs. Obviously catching a fish out in the middle of the oceanand getting it to the middle of the United States, there are transportation costs that are present that if wewent to aquaculture we could probably diminish. There are also some very nice balances that can bedone using excess heat from certain processes. One of the major costs for aquaculture is keeping thewater the right temperature. So some of the things that need to be done, a lot of good work is alreadygoing on, and I think the good news is that there are a lot of very good scientists doing a lot of veryresponsible work to get high-omega-3, selenium-rich fish developing as an aquaculture product forAmerican consumers.
Chris Kresser: Well, great. So let’s talk a little bit about how people can find some more information onthis. On my website, the original article that I wrote about this where I first cited your research, Dr. Ralston,
is called Is eating fish safe? A lot safer than not eating fish! And I will link to that in the
show notes. You, Dr. Ralston, sent me a link to a great documentary. It’s about 25 minutes long. It coversthese issues in a way that’s really accessible to people even without a science background. So can youtell us where people can find that?
Dr. Nicholas Ralston: OK, that one is by PBS, and so most of the public broadcasters across the countryare starting to pick it up. That one actually has won a series of awards. I should have my colleague, LaurieRaymond, here. She was advisory on the making of the documentary. But we do have an online version
that can be watched at our website, and our website is UNDEERC.org, for University of North Dakota
Energy and Environmental Research Center. That’s the department that we’re a part of. And then
UNDEERC.org/Fish, and that’ll take them right to the information about it, and one of the headers is
Documentary, and that’ll take them right into it.
Chris Kresser: Great. Yeah, I watched that earlier this week. I think it’s a great resource maybe to send toyour friends, family, maybe people who won’t listen to this full podcast or read an article but would watch a20-minute documentary. There was a picture I posted in my original article with the Selenium HealthBenefit Value of ocean fish with some really easy-to-understand graphic bars. Is that a good resource, oris there another listing somewhere of the Selenium Health Benefit Value that people can access?
Dr. Nicholas Ralston: I think that a few other places are starting to post Selenium Health Benefit Values. I’m pretty sure that’s available in some of the seafood sites on the West Coast and certainly in Hawaii. Wedid our study of Pacific Ocean fish collaborating with a group in Hawaii, so I know that they have it on oneof the seafood or ocean fish study group sites in Hawaii, and perhaps for your listeners — I don’t know if
this is a podcast only or if they are able to go to your site to get this information. We’ll make sure and getthe links to those sites sent to you, too, so that you can have them available.
Chris Kresser: Great. Yeah, we can put them in the show notes. We do a full transcript for all thepodcasts and post that along with the show, so that would be helpful. I appreciate that.
Dr. Nicholas Ralston: Yeah.
Chris Kresser: So last question: What questions do you have as a researcher that you hope to answer inthe future on this topic? Or where do you think the future direction lies in this research?
Dr. Nicholas Ralston: OK, well, we’re currently initiating studies where we’re going to look at the Gulf ofMexico. We’re fairly confident that for the most part, Gulf of Mexico fish are going to be fine. We’re a littlebit concerned about some of the estuaries, so we want to look at mercury:selenium ratios in those fish. Along the Alaska coast, there are some places where some types of fish in the estuaries do havereasonably high mercury:selenium ratios, and we want to identify those and let fishermen know that thesefish collected from that certain estuary might be cause for concern. But nationwide, we’re intending todevelop the continuing EPA work that we’ve initiated and look more and more carefully atmercury:selenium molar ratios in freshwater bodies across the United States because as I mentioned, 98%of the lakes, rivers, and streams seem to be OK, but the 2% that don’t look like they have goodmercury:selenium molar ratios in their fish, we need to look at them even more carefully and lakes fromthat entire region. Maybe there are even cases that worse than the ones that we found. So we want tospend a lot of time focusing on where are the fish that are cause for concern, focus in on them, and one ofthe interesting things that’s already been demonstrated in a series of studies across the world is that if youadd safe forms of selenium to a water body, you can retire the mercury from the fish very rapidly and verysafely. It has to be done carefully because as we talked at the start of the show, too much selenium is nota good thing, but we’re very cognizant of that. I serve on boards that are also reviewing places wherethere is too much selenium, so we’re completely aware of those risks, but so long as we use the low levelsof addition that we intend to use, the safe forms that we intend to use, studies in Sweden have shown thatyou can diminish the amount of mercury in freshwater fish more than 80% in just three years.
Chris Kresser: Wow. That’s great news.
Dr. Nicholas Ralston: Yeah, so we’re hoping to start doing some preliminary studies of that nature withspecial focus on these areas where there are high-mercury, low-selenium fish.
Chris Kresser: Thank you so much, Dr. Ralston, for coming on the show. I really appreciate it, and I lookforward to seeing the outcome of some of this new research you’re doing.
Dr. Nicholas Ralston: Well, I tremendously appreciate the chance to share this information, and I reallyappreciate having folks like you that are anxious to get the right information out to the public.
Steve Wright: All right, thanks for listening to the podcast today. We covered a lot of topics. I learned alot, and I’m sure you did, too. If you have any questions for any upcoming Q&A shows we’re gonna do,
please head over to ChrisKresser.com and use the podcast submission link. If you enjoyed listening
to the show today, we’d really appreciate it if you’d head over to iTunes and leave us a review. It helps usget our message out to more people like yourself who might be in need of this kind of information. Thanksand we’ll talk to you soon.
peterFEBRUARY 21, 2014 AT 12:10 PM
A toxicologist at my university talked about the topic of mercury in fish too. After one of his lectures he said, therewas a doctor coming to him and told him that he eats a tin of tuna every day. He tested the doc and he discoveredthe highest mercury load he had ever seen. How this can be true if the mercury in tuna wouldnt be a problem?
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Omega3MovementMARCH 17, 2015 AT 10:57 AM
I would say always trust your own judgment. Researchers contradict each other every time. Also mind themoderation. Fish is great. We advise everyone to eat fish, but in moderation. Especially large fish like Tuna.
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AceDECEMBER 13, 2013 AT 11:04 AM
Also wondering about radiation’s effect on fish? Does the radiation exposure after the Japan reactor problem withthe tsunami change anything about recommendations for fish from the pacific ocean? Thanks Chris!
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DavidSEPTEMBER 25, 2013 AT 3:00 AM
Table 2 of Bourdineaud, J. P., Dietary Mercury Exposure Resulted in Behavioral Differences in Mice Contaminatedwith Fish-Associated Methylmercury Compared to Methylmercury Chloride Added to Diet.
To me it seems like the fish diet has a Se/Hg ratio 2:1, MeHg diet 1.2:2.Shouldn’t both these ratios be protective? or am I missing something?
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matthkMARCH 27, 2013 AT 9:32 PM
LOVED this podcast, thanks Chris and Dr Ralston!Just one point (I’m writing from Australia):
Dr Ralston commented on shark-meat in fish & chips in NZ.“…shark meats, which nobody would do that now, but back in that time, apparently they were catching shark and itseemed like it was usable for that purpose…”
It’s not an ‘oldie-timey’ practice at all. In Australia and New Zealand, shark is often the MOST common fish in ourlocal take-away fish & chips. We call it ‘flake’ here in Oz. It’s usually gummy shark though it may also be WhiskeryShark, School Shark, Saw Shark, Elephant Fish, any of the Dogfish family or any one of a variety of other sharks andeven rays. It’s never (as far as I can tell) large shark though.Just thought you’d like to know.Cheers,Matt
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BethJANUARY 10, 2013 AT 8:20 AM
Hi Chris. I just listened to this podcast, and a question arose. I was exposed to large amounts of mercury when I hadthe last of my amalgam fillings taken out about a year ago. I had all of the symptoms – horrible depression, anxiety,hopelessness, etc. It was horrible. I started feeling better when I started supplementing with Lugol’s iodine, andconsequently, with Selenomethionine. But I’ve always suspected that my tissues had ferreted away the excessmercury. I recently had a lot of labs run, and one of the things that was tested was my selenium level, which wasabove the recommended range (although not dangerously high, by any means). Is it possible to be mercury toxic ifyour body has high levels of selenium? I’ve been contemplating doing a DMPS urine provocation test, but am nowwondering if it would be worth it. I don’t know what your take on kinesiology is (I’m not really sure how I feel about iteither), but I tested negative for mercury with 2 different kinesiologists, using muscle response testing. I’d love tohear your opinion.
He also has specific protocols for mercury detoxification. Dr. Andrew Hall Cutler is also another resource onthis issue.
I would avoid Selenomethionine and either get it from whole food or an organically bound yeast basedsource, which has far less toxicity concerns and far greater antioxidant activity. The book “Life Bridge”documents the studies behind this.
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Glenn AtkissonDECEMBER 28, 2012 AT 4:11 PM
Steve, Jackie, I could write a ton on this to you, but the best thing to do is go to another source, that is more or lessin agreement with Peskin, but may be more concise, and easier to read. The short quick answer to what the bodycan/can’t do with parent omega-3 is that the “inefficiency” of converting parent omega-3 to DHA, etc. is not valid.The body converts what it needs. But not the entire amount of parent omega-3. There is no law of the universe thatsays all alpha Linolenic Acid must be converted to DHA, EPA, etc. There are significant other uses for both theparent omega-6 and the parent omega-3 in the human body. Fish oil gives you none of these, but only the 2derivatives, DHA and EPA.But Peskin is right about overdosing. People who have rid themselves of excess, and toxic omega-6 by changing toorganic, free-range meats, eggs, etc, while also cutting out all junk foods will probably be taking in close to an idealratio of omega-6/omega-3. That is, what we took in up until the last 100 years. So if these people also take omega-3supplements, they can be over dosing.Read this, and continue until you come to the case histories at the end. The doctors are continually treating patientswho have been taking omega-3 supplements without measuring what their bodies already contain. The patients areending up with some serious physical and psychological problems.
Patients can be prescribed high doses of omega-3, regardless of source (fish oil or flaxseed or?) and they can beginto improve, because they have been eating an excess of omega-6. However, if they are at the same timetransitioning to a healthy diet which does not have ruined omega-6 as from trans fats, overheated or otherwiserancid fats, they will in a few months be getting too much omega-3. Then new symptoms show up. A John HopkinsRed Blood Cell Fatty Acid Test will immediately show the problem, which will be a ratio of omega-6 to omega-3 thatis TOO LOW. The opposite of what is supposed to be the typical American condition due to over use of both junkfoods, and grain-fed meat and eggs.Thus, the logic of Peskin is correct. He counsels to take a supplement that is already balanced in polyunsaturatedfats, so you do not upset the balance. However, his idea of the proper ratio is a bit different that that used in thepaper I quote. Peskin aims for about 2:1, and the paper I cite uses 4:1, a number that has been found to work inmany tests, and also is the number found in most wild game meats.Best of Health.
George @ the High Fat Hep C DietJANUARY 14, 2013 AT 3:28 AM
This paper, to me, settles the question of what is better – parent EFAs (ALA and LA) or animal EFAs (EPA,DHA and AA). look at table one to see how much more effective the latter and, and how much lessexposure to PUFA is required when fish oil, not vegetable oil is the source. And compare the death ratebetween the two types of EFA.
Hi Chris Kresser, what do you think of the http://www.quackwatch.com website and it’s author, Dr.
Stephen Barrett? Do you recommend his information as credible? Or, does he have some good information andsome not-so-recommendable information? Thanks!
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SteveDECEMBER 28, 2012 AT 1:09 PM
@jake3_14 – http://www.quackwatch.com is a list of hundreds of people, including Dr. Mercola and
Russell Blaylock. I didn’t find ANY conclusive evidence about Brian Peskin on the link you sent. People get sued allthe time, including the doctor who runs Quackwatch. The link was last updated in 2003. It’s 9 years later and BrianPeskin hasn’t been convicted of anything and YES Supplements are still being sold.
Please don’t misunderstand me: I have NO interest in defending Brian Peskin, but I AM interested in knowingwhether his PEOs are beneficial or not. The link you posted does not provide that, and no one else has respondedwith any information. Can anyone provide some helpful, evidence-based information on the benefits/non-benefits ofusing PEOs instead of Fish Oil? Thank you!
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SteveDECEMBER 2, 2012 AT 1:15 PM
Hi Chris, Thanks so much for this information! I have received some conflicting information from a very good friendabout DHA, and would love your input. She has struggled with diet/nutrition/allergies etc for several decades, but
has finally found relief using in Brian Peskin’s research and his Parent Essential Fatty Acids (PEFAs), also known asParent Essential Oils (PEO’s). Have you heard of them/his research? I’m on the fence about whether to stay withDHA and using fish as a primary source of DHA (for good heart/circulatory reasons) vs. PEOs. His PEOs are “organic,unprocessed nuts and seeds, cold-pressed oils made from those nuts and seeds, and whole, unpasteurized,unhomogenised dairy products.” I find it interesting that your research has shown that ‘plant sources don’t cut it,because only a very small percentage…of the short-chain omega-3 fats found in plants get converted into thebeneficial long-chain omega-3 fat DHA.’ His argument is that DHA is a derivative form of omega’s and that the bodydoes not need the derivative. Instead, he says that the body needs the parent form (found in the PEOs) and will thenconvert the amount it needs. Also, I think he’s talking about the body converting Omega 6s into Omega 3s…I didn’tcome across info about converting short into long chain Omega 3s…but maybe I need to do more research. Hisconcern is that Americans who are supplementing w/ Omega 3s have been overdosing on omega 3 and the heartdisease and cancer rates have been increasing. Everyone always cautions “you have to make sure you are gettingthe right ratio” but w/o a home test kit for Omega 6 : Omega 3, it seems hard to do. Any help is greatly appreciated!Thank you!
So, any comments you have on the above is great! Plus, I had a few specific questions:1) Is it possible that his inclusion of dairy products in his PEOs make up for the inability of the body to convertenough plant sources, thereby allowing the body to convert enough of the parent form into the derivative forms, asneeded (and preventing overdosing of Omega 3s)?2) What do you think of his research that the body doesn’t need the derivative form DHA, but instead needs the“parent form” found in PEOs?3)
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jackieDECEMBER 2, 2012 AT 3:57 PM
steve, i’ve had the same questions for a while, but can’t seem to get any answers from anyone :-/
What about farm raised fish? Should we avoid due to toxins? Should we embrace to help protect the oceans? It’sgreat that the doctor has evidence that ocean fish is good for for us, but I can’t imagine the oceans can sustainincreased consumption.
Soooo… I had dropped the “vaccine” issue as being a reason for my child’s autism but am now wondering ifinjecting babies (with low selenium levels) with ethyl mercury maybe used up all the selenium enzymes and theleftover unbound mercury is what caused the tissue damage and hence autism….? Wish Chris would have askedDr.’s opinion of the mercury in vaccines.
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The High Fat Hep C DietOCTOBER 31, 2012 AT 1:07 PM
Chris, you’re into Oriental Medicine, right?It’s always been seen by western doctors as a black mark on traditional Chinese Medicine that mercury, in the formof cinnibar was a popular medicine.But – if mercury leaches excess selenium from the body, it’s easy to see how cinnibar got its reputation as apowerful aid to health and longevity.There are parts of China where selenosis is endemic due to high levels in soil and water.“The most frequently reported symptoms of selenosis are hair and nail brittleness and loss. Other symptoms mayinclude gastrointestinal disturbances, skin rashes, a garlic breath odor, fatigue, irritability, and nervous systemabnormalities. In an area of China with a high prevalence of selenosis, toxic effects occurred with increasingfrequency when blood selenium concentrations reached a level corresponding to an intake of 850 mcg/day.”
If cinnibar was used first in this area, and relieved the symptoms of selenium toxicity, its reputation was notundeserved. It would have been a lifesaver, and had dramatic and obvious effects in reversing disease.
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george hendersonOCTOBER 26, 2012 AT 5:50 PM
Selenium does detoxify mercury IRL: Thanks to Mario Iwakura at PHD Q&A for this link
http://www.ncbi.nlm.nih.gov/pubmed/23033886
Environ Sci Technol. 2012 Oct 16;46(20):11313-8.
Organic selenium supplementation increases mercury excretion and decreases oxidative damage in long-termmercury-exposed residents from wanshan, china.Li YF, Dong Z, Chen C, Li B, Gao Y, Qu L, Wang T, Fu X, Zhao Y, Chai Z.
Due to a long history of extensive mercury mining and smelting activities, local residents in Wanshan, China, aresuffering from elevated mercury exposure. The objective of the present study was to study the effects of oralsupplementation with selenium-enriched yeast in these long-term mercury-exposed populations. One hundred andthree volunteers from Wanshan area were recruited and 53 of them were supplemented with 100 μg of organicselenium daily as selenium-enriched yeast while 50 of them were supplemented with the nonselenium-enrichedyeast for 3 months. The effects of selenium supplementation on urinary mercury, selenium, and oxidative stress-related biomarkers including malondialdehyde and 8-hydroxy-2-deoxyguanosine were assessed. This 3-monthselenium supplementation trial indicated that organic selenium supplementation could increase mercury excretionand decrease urinary malondialdehyde and 8-hydroxy-2-deoxyguanosine levels in local residents.
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Victor VenemaNOVEMBER 3, 2012 AT 2:51 PM
From the Dong et al. (2012) article:“Fifty-three volunteers (27 men and 26 women) were supplemented with one tablet (100 μg Se/tablet) ofSe-enriched yeast (SelenoPrecise, Pharma Nord, Denmark) daily… ”
“50 volunteers (25 men and 25 women) were supplemented with one identical-looking non-Se-enrichedyeast tablet (Pharma Nord, Denmark) as the placebo group.”
“In the supplementation group, the urinary Hg level increased significantly after 30 days (d30), from 18.3 ±0.5 ng/mL to 31.8 ± 1.5 ng/mL and increased to 50.4 ± 3.1 ng/mL on d90.”
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GabrielOCTOBER 26, 2012 AT 12:58 PM
Can’t seem to find a more comprehensive list of Se Health Benefit Values than this one:
Thank you for this article! I have to explain the mercury thing to someone new each month it seems. Nice to havearticles I can send them to.
I researched mercury in fish when I stopped being a vegetarian. I love fish, and I’m comfortable eating it. I reachedthe same conclusions after my research, learning about the different types of mercury and the actions of selenium. Ican’t understand why the government has been so reactionary about fish. I’ve eaten fish regularly all my life, save ayear and a half of being a vegetarian. I now eat fish once or twice each day (tuna and salmon mostly). I also avoidindustrialized foods and consume pastured eggs and butter. I look younger than I am and I rarely go to the doctorfor anything.
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Chris CNOVEMBER 13, 2014 AT 10:10 PM
Perhaps to deflect attention away from the fact that they let dentists fill your mouth with enough mercury tokill you 1000 times over?
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The High Fat Hep C DietOCTOBER 23, 2012 AT 4:13 PM
Sorry about that.Anyway, some seaweeds and other algae do contain DHA and EPA. The colder the water it grows in, the more likely
the algae will synthesise longer-chain fatty acids from ALA. http://www.omega-3-efa.com/algae-
supplements.html
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The High Fat Hep C DietOCTOBER 23, 2012 AT 1:01 PM
How would compare fermented chia seeds (or fermented anything that is high in Omega 3s that’s a plant source) tofreshwater fish such as you mentioned when it comes to Omega 3 content? This is an important question for peoplewho are vegetarians and vegans (and for those who do not like seafood!).
Thanks
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Chris KresserOCTOBER 21, 2012 AT 6:33 AM
They don’t really compare at all, unfortunately (for vegans and vegetarians). Plant-based forms of omega-3(alpha linolenic acid) are poorly converted to DHA. In fact, less than 0.5% (1/2 of one percent) getsconverted – and that’s in a healthy person. The number is smaller in those deficient in the nutrients needed
for conversion (which often includes vegetarians and vegans), and those who are ill. Read this articlefor more info. The only suitable alternative for vegans and vegetarians are microalgae supplements thatcontain DHA. That’s where the fish get it from.
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The High Fat Hep C DietOCTOBER 20, 2012 AT 5:54 PM
http://www.ncbi.nlm.nih.gov/pubmed/19374471
“the potential Hg-Se compounds that are responsible for the antagonism at the molecular level (i.e.,bis[methylmercuric]selenide, methylmercury selenocysteinate, selenoprotein P-bound HgSe clusters, and thebiominerals HgSe(x)S(1-x)). The presence of these compounds in biological systems has been suggested by director indirect evidence, and their chemical properties support their potentially key roles in alleviating the toxicity of Hgand Se (at high Hg and Se exposures, respectively) and deficiency of Se (at low Se exposures).”
http://www.ncbi.nlm.nih.gov/pubmed/11087435
“Mercuric chloride toxicity in mammals can be overcome by co-administration of sodium selenite. We report a studyof the mutual detoxification product in rabbit plasma, and of a Hg-Se-S-containing species synthesized by additionof equimolar mercuric chloride and sodium selenite to aqueous, buffered glutathione.”
It is probably the mercury to DHA ratio one should consider in fish, if the diet is already supplying selenium.
Hi Chris,Dr. Ralston ducked two questions you asked:– What form of selenium is most effective/bioavailable? Ralston simply didn’t answer the question.– Is eating more fish environmentally sustainable? Ralston’s response amounted to “we should take better care ofthe ocean.”
Also, it seems that these questions still need to be asked:– Which form(s) of mercury binds to selenium still needs to be answered.– What the body does with the mercury-selenium pair?– Even though studies show PCB not to be a major contaminant, how do you weigh the benefits of selenium againstthe risks of other toxins in fish, e.g., those from algae blooms (ciguatoxin, domoic acid), and those from radiationleaks (the cesium in tuna on the U.S. west coast recently that stemmed from the damaged Sendai plants)?
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MartineOCTOBER 20, 2012 AT 12:20 PM
Thank you Chris for yet another quality piece of research.
For those readers who like myself have better access to freshwater fish than ocean fish and are wondering aboutspecific Selenium levels inland, follow this link to the USGS.
It is a map of the lower 48 states with soil Selenium data by county. I searched all over for Selenium levels ofindividual lakes but didn’t find it. But in general I understand that Se levels in surface waters are dependent on soilSe levels so this is at least a starting point to help determine whether the freshwater fish in your area are likely tocontain Selenium.
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KarlOCTOBER 19, 2012 AT 10:47 PM
I like swordfish, but it has more mercury than selenium. I don’t eat it too often though. I eat plenty of other fish andbeef which have selenium. Would my routine beef and other fish consumption counteract my occasional intake ofmercury in swordfish or not?
Thank you Chris for this interesting and informative interview. And sorry for my english, I am not native english
speaker. But hope it is at least understandable.
I have two questions on this matter. Does mercury produce any harm other than inactivating selenoenzymes thatprevent oxidative damage? If yes, I would say that having more selenium than mercury is not completely protective.
And does frying fish destroy Omega 3 FA by oxidizing them (or in any other way)?
Best regards,Dejan
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ElizabethOCTOBER 18, 2012 AT 9:29 AM
The issue remains that many people are still mercury toxic. I realize that this interview was more about exoneratingfish as a source of mercury toxicity, but how can this information help those who already are mercury toxic?
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DavidMOCTOBER 18, 2012 AT 8:50 AM
One other thing that should be mentioned here is how to prepare fish if you decide to eat fish. How does cookingaffect the selenium protection? Certainly overcooking the fish or frying the fish is not advisable and will damage then-3’s and the protein and other nutrients. Frying will introduce acrylamides and if you eat fried fish, it usually has acrust and the crust is usually wheat based and wheat is not healthy. Plus the oil it is fried in can be a problem. So ingeneral fried fish should probably be avoided.
I know a couple of years ago that the actor Jeremy Piven who eats a lot of sushi actually got mercury poisoning(maybe he was eating whale meat) and had to stop film production for a while to recover. This makes me wonder ifeating raw fish is more of a concern? I know that raw fish can and usually do contain harmful parasites and othermicro-organisms, but would like to understand if raw if more dangerous from a mercury/toxin perspective?
My guess is that very lightly cooking/baking the fish is the best way to go. But I love raw sushi and would like tounderstand if raw is more dangerous or not from a mercury perspective. Thanks for any input.
My concern is with ocean fish and the radiation exposure. What evidence do you have to this regard? We ateocean-caught fish exclusively until that was exposed. Now I feel more comfortable with farmed fish. How do wedecide which is better? Any tips? Thanks!
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DavidMOCTOBER 18, 2012 AT 7:43 AM
Thanks chris for this interview, I think it is very good information! I appreciate allthat you are doing! But I think there is some misinformation in this interview andsome missing information…1. There is not only concern about mercury in fish, but other toxins, includingdioxins and PCBs. Im not sure of what studies exist about these toxins, but would liketo know? And moreover, mercury is increasing in the oceans, thanks to the coalindustry for one, so we have to keep this in mind.2. To say any source of selenium is beneficial is really not true. There are good studies showing that syntheticselenium (such as selenomethionine) is not nearly aseffective as whole food or yeast based selenium. These studies show that syntheticselenium has almost no antioxidant capacity and can be toxic even in low doses. Thereis much less concern with toxicity if you get it through whole foods, brazil nutsbeing the best source. The book “The Life Bridge” documents these studies.3. Personally, even if selenium protects against mercury in the tissue, I would rathernot have the mercury in my tissue. The Weston A Price foundation has shown that if gutflora is optimal and healthy that much less mercury gets into the blood and thus thetissue. So, if you are eating fish, healthy probiotics can significantly reduce theamount of mercury getting into the blood in the first place. The best way to make yourgut flora healthy is by eating fermented foods, such as fermented coconut water orfermented vegetables (e.g. cabbage)4. To say that most people eating a healthy diet are sufficient in selenium is alittle misleading because most people are deficient in selenium, which implies mostpeople dont eat a healthy diet, so need at least need to supplement or change theirdiet.5. This interview implies that selenium, in the right form, is only mildly cancerpreventive. I have heard several cancer specialists and selenium experts say thatselenium is the number one cancer preventative on the planet. So, in my opinion,selenium is much more significant for cancer prevention than implied by thisinterview.6. These studies that show pregnant women have higher IQ babies if eating fish makesme wonder if there have there been comparison studies with women who eat fish versuswomen who consume fish oil? In other words can we get the same benefits from consuminga high quality fish oil without contaminants (like mercury) as consuming fish? Irealize fish oil is a controversial subject and we have to consider krill oil,calamari oil, fermented fish oil, and high quality pharmaceutical grade fish oil. You,chris, have written some really good articles on fish oil, so I wish this interviewwould have compared the two. We know that mercury crosses the placental barrier andwill get into the fetus, and even if there is sufficient selenium to protect againstdamage, I think most mothers would rather not be putting mercury into their child andwould opt to get the omega 3’s (DHA, EPA) from another source if possible.7. The best way to detoxify from mercury is not really brought up. There are severalreally good detoxification methods. For example, Dr. Andrew Hall Cutler’s method using
Alpha Lipoic Acid, DMSA, and DPMS is proven to be quite effective and safe.8. Mercury comes in several different forms, elemental(Hg), inorganic (HG2+), methyl(MeHg), and ethyl (EtHg). These forms all act differently in the body and should bedistinguished. For example, the form introduced to the body by amalgams is elementaland by fish is methyl or more correctly methyl mercury cysteine. The form found invaccines is ethyl. The way these forms act on the body is not mentioned but is verydifferent and is important to understand.The form found in fish is highly absorbableinto the blood via the gut and so if you dont want it in your blood healthy gut florais all the more important. I am curious about how selenium protects against thedifferent kinds of mercury. Does it protect against all different forms? I suspect thedoctor was only talking about inorganic mercury, HG2+, which most of the forms readilybreak down to once in the body or was he talking about all the different forms?
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HMOCTOBER 18, 2012 AT 6:57 AM
Fantastic information. Thank you so much for sharing your efforts Chris. It’s making such a difference to me and tomany others.
Could someone please reply and explain to me how to get to ‘the show notes’. I’m not that savvy with all this stuff.
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DavidOCTOBER 18, 2012 AT 6:14 AM
Dr Mercola claims the problem with fish are all the PCBs and other toxins, is that a concern?
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Chris KresserOCTOBER 18, 2012 AT 6:45 AM
In short: no. I cover that here: http://chriskresser.com/is-eating-fish-safe-a-lot-
Chris, I read your link here and great article. But had a question about the following statement “Thehighest dietary sources of PCBs and dioxins are not fish, but beef, chicken and pork (34%), dairyproducts (30%) and vegetables (22%). Fish constitute only 9% of our dietary intake of thesechemicals.”
Is this the case with organic beef, chicken, pork, dairy, and vegetables? If not we can choose tobuy organic to avoid them, however there is no way to avoid them in fish – there is no such thingas organic wild caught fish (unfortunately). So then fish could become the largest source of thesetoxins. I would like to hear your comments on why I would choose contaminated fish over cleanfish oil or fermented fish oil or krill oil or calamari oil? Even though eating fish has many benefits asyou say, can we get these benefits from other cleaner safer sources? My opinion is whole food isalmost always better for anything, including n-3’s DHA and EPA, but if the whole food (in this casefish) is even slightly contaminated and I can get near the same benefit from a non contaminatedsupplemental form, wouldn’t that be a better choice?
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KerryOCTOBER 17, 2012 AT 1:36 PM
I understand that shark meat is high in mercury, but what about shark OIL? Is it safe to consume?
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The High Fat Hep C DietOCTOBER 17, 2012 AT 1:22 PM
@ Mike, you are forgetting that Se is only active in selenocysteine.There is no mercury-cysteine analogue tocompete with this. Mercury depletes selenium by binding directly to selenium.
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The High Fat Hep C DietOCTOBER 17, 2012 AT 1:20 PM
It is similar to the argument about oysters; they can be high in cadmium, but as they are also a very rich source ofzinc, which cadmium displaces, this cancels out the risk of toxicity.
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jake3_14OCTOBER 21, 2012 AT 7:11 PM
If cadmium displaces zinc in the oyster, then wouldn’t oysters be high in cadmium, not zinc, and therefore,
The High Fat Hep C DietOCTOBER 23, 2012 AT 4:49 PM
If humans get enough zinc, cadmium will not displace it, but if we are zinc-deficient, we arevulnerable to cadmium or lead toxicity. The more cadmium or lead we are exposed to, the morezinc we need. A highly polluted oyster is a highly polluted oyster, but relatively high levels ofcadmium and zinc have been found in oysters growing in the open ocean far from industry, as in
this example: http://tinyurl.com/8uws6hswithout resulting in cadium toxicity. The levels in polluted oysters are about twice as high as in thisexample.
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AnneOCTOBER 17, 2012 AT 12:43 PM
What about people who have toxic burdens and autoimmune diseases (toxic overload and inability to processfurther toxins, especially heavy metals)? Why is this important issue not addressed in your article? My doctor says Ishould not eat any tuna until I’m symptom free.
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Chris KresserOCTOBER 18, 2012 AT 6:50 AM
The point is that mercury causes harm by inactivating selenoenzymes that prevent oxidative damage. If youhave normal selenium intake and activity of selenoenzymes, and if a fish has more selenium than mercury,then it shouldn’t be a problem.
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David HammondJULY 5, 2014 AT 6:59 AM
Hi Chris,
Personally, I am not convinced that the high levels of mercury in fish such as tuna and swordfishare safe even if they exist in the presence of equimolar or higher concentrations of selenium.
The definitive study on this issue is Chang’s (1), in which 16 kittens were fed a diet of tunacontaining 0.3 to 0.5 ppm mercury, plus supplementary nutrients and vitamins. After a period ofseven months, two of the cats had mild ataxia and one had severe ataxia. The cats were sacrificedat 11 months and autopsy revealed extensive liver damage including damage to the mitochondria.In this case the selenium in the fish was not protective.
I agree with Dr Ralston’s statement in his review, Mercury: selenium interactions and healthimplications (2), where he says “the ‘protective effect’ of selenium against mercury exposure mayactually be backwards. Mercury’s propensity for selenium sequestration in the brain and endocrinetissues may inhibit formation of essential Se-dependent proteins (selenoproteins). Henceselenium’s ‘protective effect’ against mercury toxicity may simply reflect the importance ofmaintaining sufficient free selenium to support normal selenium-dependent enzyme synthesis andactivity.” But even maintaining optimal levels of selenium may not be enough to completely nullifymercury’s toxic effects.
In the same review he mentions the study by Friedman into the protective effects of driedswordfish on methylmercury toxicity in rats. He states that rats fed a diet of swordfish andmethylmercury showed no signs of neurotoxic effects, while rats fed a control diet spiked withmethylmercury without swordfish did. Dr Ralston attributes this to the protective effects ofselenium.
In spite of the proposed protective effect of selenium, both the control group and the experimentalgroups died, at 4.6 and 5.3 weeks respectively. It should also be noted that the control dietincluded 15% casein which has been shown to reduce mercury excretion in rats (3), and thus mayhave exacerbated the effects of mercury toxicity in the control rats.
These studies do not take into account the long-term effects of mercury exposure. The lower thedose of mercury, the greater the delay in the manifestation of symptoms. Deborah Rice fedmonkeys a diet which included 50 micrograms of methylmercury per day for 7 years (4). Aftercessation, blood levels quickly dropped to normal. When the monkeys were tested at 13 years ofage they displayed clumsiness and loss of fine motor skills as well as decreased sensitivity totouch. Humans are exposed to mercury for decades and have longer to develop overt signs ofmercury toxicity.
One of the problems with the studies from the Seychelles and the Faroe Islands on the effect ofmethylmercury on neurodevelopment is that they rely on hair testing of mercury levels. This isoften accurate, but does not take into account the fact that mercury disrupts cellular transport dueto its affinity for sulfhydryl molecules. These molecules often form the active site in cellulartransport proteins. Mercury binds to these active sites, altering mineral transport. This can result inhair readings for mercury and other toxic elements that are artificially low. Thus children with highexposure may actually be classed as having low exposure. Hair analysis actually provides ameasure of how much mercury is being excreted. The most important factor is how much mercuryis being retained in the body – but that is difficult to measure.
Amy Holmes found that autistic children, even though they had higher exposures to mercurythrough their mothers’ dental amalgams and Rhogam injections, had lower levels of mercury intheir hair, implying a reduced ability to excrete mercury (5). The following hair test illustrates theability of mercury to disrupt mineral transport in a child with ADHD and a weak immune system –
This is clearly an abnormal distribution of elements (all except one of the essential elements arebelow the 50th percentile) associated with a low reading for mercury.
It may be safe for some individuals with optimal antioxidant and metallothionein status to consumetuna and other high mercury fish, but I think for many it would be safer to stick to fish such as
sardines and salmon, which have high levels of omega 3s, but much lower levels of mercury.
Thanks,
David Hammondauthor – Mercury Poisoning: The Undiagnosed Epidemic.
References1 Chang, L. W., & Yamaguchi, S. (1974). Ultrastructural changes in the liver after long-term diet ofmercury-contaminated tuna. Environmental Research, 7(2), 133-148.
2 Raymond, L. J., & Ralston, N. V. (2004). Mercury: selenium interactions and health implications.Seychelles Medical and Dental Journal, 7(1), 72-77.
3 Rowland, I. R., Robinson, R. D., & Doherty, R. A. (1984). Effects of diet on mercury metabolism andexcretion in mice given methylmercury: role of gut flora. Archives of Environmental Health: AnInternational Journal, 39(6), 401-408.
4 Rice DC. Delayed neurotoxicity in monkeys exposed developmentally to methylmercury.Neurotoxicology. 1989 Winter; 10(4):6450-50.
5 Holmes, A. S., Blaxill, M. F., & Haley, B. E. (2003). Reduced levels of mercury in first baby haircutsof autistic children. International journal of toxicology, 22(4), 277-285.
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jackieOCTOBER 17, 2012 AT 10:39 AM
oh also, whenever i eat fish (salmon or sardines or anchovies), i take chlorella. i’m thinking that would help withbinding the mercury.
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Sally OhAUGUST 9, 2013 AT 8:04 AM
Someone above mentioned Dr. Andrew Cutler and his frequent-dose chelation therapy. Cutler is a scientistdoctor, not a medical doctor.
Chlorella cannot bind with mercury, nor carry it out of the body except possibly some by accident. It’s not atrue chelator as it contains just one thiol (a molecule that binds to mercury). A true chelator must containtwo thiols so it can bind to mercury tightly and escort it out of the body.
Alpha lipoic acid ALA), dmsa and dmps all contain two and are the only safe chelators to use, according toCutler.
The only things chlorella (and cilantro) can do is move mercury around and that can do more harm thangood, especially chlorella with lipoic acid (some health shops sell this as a combination tablet). Becauselipoic acid crosses the blood brain barrier, if you are just moving any of that mercury around, you couldactually move some TO the brain.
Also some forms of chlorella actually contain mercury.
To find out more about Culter’s protocol, search the yahoo groups for frequent-dose-chelation.
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jackieOCTOBER 17, 2012 AT 10:38 AM
i love sardines, but here in the US (or at least in ohio), they only come in cans. i buy the ones that say “bpa free”(wild planet), but i still hate eating out of cans. even though there’s no bpa, i’m sure there’s lots of other God knowswhat, like aluminum or tin. anyone have a good solution or a good source of fresh sardines? also, i’m wonderingabout the radiation in the wild planet sardines, as they are from the california coast…..
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Sally OhAUGUST 9, 2013 AT 7:51 AM
We can get frozen sardines from a local fish distributor. You might ask your local grocery store can they getthem frozen. They come 6 (big) sardines in a bag.
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BrianOCTOBER 17, 2012 AT 9:25 AM
Amalgam dental fillings are by far the top source of mercury. Mothers with these half-mercury fillings pass mercuryon to their children. Google “Andrew Cutler mercury” for how to correctly diagnose and fix this problem.
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Glenn AtkissonOCTOBER 17, 2012 AT 9:16 AM
Fantastic interview, Chris. A definite vindication of fish as a threat to health. So many people can feel so relieved.It would be interesting to see an article now on how much selenium can aid in protection from the threat ofamalgam fillings. Possibly there also, there is less threat than imagined provided sufficient selenium is on board.I still wonder about your comment on DHA. Though it wasn’t addressed in the interview, your intro touches on it’s
importance, and the importance of obtaining it from animal sources. I would never disagree with the value of animal/ fish sources of nourishment, but always wonder how the infant brain is able to get a good supply of DHA, whichthen hardly needs additions or replenishment during life, regardless of the mother’s diet during pregnancy, or thefood the child is given from infancy on. I mean over millions of years this has taken place in spite of what sciencetells us is a very low conversion rate of parent alpha-linolenic acid into DHA. I can only infer that either man hasalways eaten brain, or fish, as these are the main sources of DHA in the human diet. But it seems there must behuman tribes who eat neither brain nor fish. And there are certainly many animals who never eat brain or fish. Couldit be that science is also wrong on the significance of this “poor conversion” of fats into the DHA that we need in ourbrains and nervous system? Could it be that, as for every other nutrient, the body converts only what it actuallyneeds of a substance into another substance?
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AmyOCTOBER 17, 2012 AT 9:13 AM
I know that omega-3 is helpful for lots of reasons, including inflammation, which is important to me because I haveHashimotos. The question I cannot get anyone to answer is, if you have low platelets does taking omega-3 makelow platelets worse or is it harmful? I have read a lot about not taking fish oil before surgery or with blood thinners,etc. but can’t find anything about low platelets.
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MikeOCTOBER 17, 2012 AT 9:13 AM
Question for the Dr. – your description of selenoenzymes, selenium, and mercury’s respective interactions doesn’tquite make sense to me. Mercury competes with selenium for binding, mercury binds much stronger, therefore youalready have a surplus of selenium. Increasing selenium would only increase tissue, cellular, and plasma levels butwould not directly result in increasing binding potential as this is dictated by elemental/molecular properties.Obviously this can be driven by increasing selenium vs. mercury; however, once saturated, this would prove futile.
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jake3_14OCTOBER 20, 2012 AT 11:58 AM
Mike,I don’t understand your explanation. would you please dumb it down for some of us? For instance, whenyou say that “Mercury competes with selenium for binding,” what is being bound? My interpretation of Dr.Ralston’s comments was that selenium normally gets incorporated into 30 enzymes, but that mercury’sbinding affinity for selenium is so strong that it takes precedence over the normal biological activity. Is thatthe competition you mean?
Thanks for bringing Dr. Ralston on the show Chris, some really, really interesting points. Didn’t realize how thewhole mercury scare got started with Minamata. The flaws pointed out in the SuppVersity study made total sense aswell.
What are your thoughts on having 3-4 brazil nuts every morning to increase selenium intake if fish eating is only a1x/wk occurence?
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jake3_14OCTOBER 19, 2012 AT 6:36 PM
1 oz. of brazil nuts has 9443 mg. of O6 fatty acids. In the past, Chris has recommended that O6 fats be 3.2%of your daily diet — at most. If he still recommends this, then even 1 oz of brazil nuts exceeds that daily limit(assuming a daily intake of 2000 kcal). If Chris has changed his mind, then the question remains how muchselenium is in a brazil nut? It’s dependent on the soil where it’s grown, and the reference values in theUSDA database are old, so there’s no way to know how much you’re getting. It might be 95 mcg, as thedatabase says, but it might be much less or much more.
But 3–4 brazil nuts seems like overkill. Dr. Ralston indicated that a daily intake of 200 was OK, whichtranslates to 2 brazil nuts/day.
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george hendersonOCTOBER 26, 2012 AT 5:46 PM
Nonsense. Brazils tested in NZ have 19mcg Se each.
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jake3_14OCTOBER 27, 2012 AT 2:40 PM
That’s interesting, George, because the USDA food database lists a single brazil nut ashaving 95.9mcg of selenium. Given this great disparity, how is a person supposed to know, or whatshould they assume about the Se content of brazil nuts?
The High-fat Hep C DietOCTOBER 27, 2012 AT 3:16 PM
I’ve read the fulltext NZ paper (Christine Thompson et al.) which is recentwhereas I don’t know where the USDA data came from. I’m relaxed becausethere has never been a case of selenosis from brazil nuts in the publishedmedical record, yet selenium from brazils (according to Dr thompson) is superiorto Se from selenite supplements for improving antioxidant defenses.
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NancyOCTOBER 17, 2012 AT 8:28 AM
What about radioactive contamination from the on-going catastrophe in Japan?
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Chris KresserOCTOBER 17, 2012 AT 8:45 AM
I’m still waiting for reliable, peer-reviewed data showing harmful levels of radioactive isotopes in fish. Ifyou’re aware of any, please send it to me.
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sydOCTOBER 17, 2012 AT 6:39 PM
That’s a really great question.
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TuckOCTOBER 17, 2012 AT 8:22 AM
Great topic. I did the research on this myself a few years ago and came to the same conclusion.
Which is not to say that you can’t get too much mercury from fish, but it’s not nearly the threat we’re led to believe.
