Vitamin A and Vitamin C

Theresa Camardo

Intro

Both Vitamin A and Vitamin C are necessary for proper immune system function.

Vitamin A

Fat-soluble “Vitamin A” is actually a term that refers to a

group of substances that include retinol (preformed Vitamin A), retinal, retinoic acid, retinyl esters.

“Vitamin A” can also refer to precursor compounds known as carotenoids.

Absorbed in the small intestine (70-90%); more than 90% located in liver

Structure of Vitamin A

Source: http://www.bio-pro.de/en/region/stern/magazin/00403/index.html

Vitamin A: Functions

Growth (production of HGH, normal functioning of osteoblasts and osteoclasts)

Reproduction Embryonic development (retinoic acid influences cell

differentiation) Vision (eye uses retinal to transduce light into neural signals and

retinoic acid to maintain cornea/conjuctival membrane differentiation which prevents xerophthalmia)

Gene expression (retinioic acid regulates expression of encoding genes for structural proteins, enzymes, extracellular matrix proteins, and retinol binding proteins and receptors)

Immune function (retinol regulates lymphocyte physiology) Glycoprotein synthesis

Carotenoids

Plant pigments – deep colors alpha-carotene, beta-carotene, lycopene,

lutein, xeaxanthin, beta-cryptoxanthin alpha-carotene, beta-carotene, and beta-

cryptoxanthin can be converted in Vitamin A (provitamin A)

Fat-soluble Absorbed in the intestine and stored in

tissues

Vitamin A: Food Sources

Preformed Vitamin A (retinol) is found in animal-based foods such as liver, dairy, and fish. Also prevalent in fortified grains

Carotenoids as provitamin A are found in darkly pigmented plant products such as spinach, broccoli, cantaloupe, carrots, and vegetable-beef/chicken soup.

All are also found in supplement form

Vitamin A: Biochemical Indicators Serum retinol and serum binding protein

Vitamin A Deficiency:Causes Absorption is enhanced by fat, and

diminished by diarrhea, intestinal infections, and infestations.

Deficiency is rare in developed nations, but common in developing countries

Vitamin A Deficiency:Consequences Most common condition is xerophthalmia

(irreversible drying of conjunctiva and cornea) Affects 3-10 million children/year Starts with night blindness, then continues into

conjuntival xerosis, Bitot’s spots, corneal xerosis, corneal ulceration, and scarring)

Decreased immune function/increased risk of infectious morbidity/mortality

No known deficiency effects from underconsumption of carotenoids.

Vitamin A Toxicity:Causes >=30,000 mcg/day for months-years is

chronic toxicity >= 150,000 mcg in single or short-term doses

is acute toxicity (less in children) Excludes beta-carotene

Vitamin A Toxicity:Consequences Acute Toxicity:

Effects are transient and include: Nausea Vomiting Headache Increased cerebrospinal fluid pressure Vertigo Blurred vision Loss of muscular coordination Bulging fontanel in infants

Chronic Toxicity: Less specific and more varied symptoms including:

Birth defects Liver abnormality Reduced bone mineral density CNS disorders Possible teratogenicity

Infants and children can also experience bone tenderness/pain, increased intracrancial pressure, desquamation, brittle nails, mouth fissures, alopecia, fever, headache, lethargy, irritability, weight loss, vomiting, and hepatomegaly.

Vitamin A DRI’s

Vitamin A DRI’s

Vitamin A DRI’s were based on assurance of adequate liver stores for age 19 – 70 YO For 1-18 YO, the adult EAR was extrapolated For 0-6 MO, average Vitamin A intake from human milk

was used For 7-12 MO, the infant EAR was extrapolated Pregnancy and lactation

Lack of evidence to determine DRI for provitamin A forms

UL was determined using risk of liver abnormalities or teratogenocity

RAE = Retinol Activity Equivalent

RAEs

Vitamin A Summary

Vitamin A is a fat-soluble vitamin important for immune function, growth, embryonic development, immunity, and vision.

Vitamin A can come as a preformed version (retinol), or as provitamin A (carotenoids).

Vitamin A DRIs are represented as Retinol Activity Equivalents (RAEs)

Vitamin A DRIs were determined using assurance of adequate liver stores

The RDA for adult males and females for Vitamin A is 900 mcg and 700 mcg, respectively.

Vitamin C

Also known as ascorbic acid Water-soluble Absorbed in intestine by an Na+ dependent

active transport (high concentrations use passive transport)

Also regulated by the kidneys (conservation and excretion)

Stored in pools throughout the body

Vitamin C

Source: http://biology.clc.uc.edu/courses/bio105/vitamin.htm

Vitamin C: Functions

Antioxidant (high reducing power) Scavenger of free radicals Cofactor for enzymes in the biosynthesis of

carnitine, collagen, NTs, and in vitro processes Reducing agent Scavenging of reactive oxidants in leukocytes,

lung mucosa, gastric mucosa Diminished lipid peroxidation

Vitamin C: Sources

Fruits and Vegetables such as citrus fruits, tomatoes, tomato juice, potatoes, brussel sprouts, cauliflower, strawberries, cabbage, spinach

Fortification Supplements 70-90% bioavailability (50% at high intakes)

Vitamin C: Biochemical Indicators Plasma and leukocyte ascorbic acid levels

Vitamin C Deficiency:Causes Rare in developed countries, although is

seen in diets that lack fruits and vegetables, older men, and lower socioeconomic status

Vitamin C Deficiency:Consequences Scurvy, which includes symptoms such as

follicular hyperkeratosis, petechiae, ecchymoses, coiled hairs, inflamed and bleeding gums, perifollicular hemorrhages, join effusions, arthralgia, impaired wound healing, dyspnea, edema, dry eyes and mouth, weakness, fatigue, depression

Infantile scurvy includes bone abnormalities, hemorrhagic symptoms, and anemia

Vitamin C Toxicity

Large doses (> 3,000 mg/day) Diarrhea and other GI disturbances

No other adverse effects

Vitamin C DRIs

Vitamin C DRIs

DRIs were determined by estimates of body pool or tissue Vitamin C levels that were considered adequate for antioxidant protection and minimal urinary loss Women have higher blood levels Smokers have a higher requirement

UL determined by occurrence of osmotic diarrhea and GI disturbances

Vitamin C Summary

Vitamin C is an important antioxidant. Vitamin C is water-soluble. Vitamin C is found in many fruits and vegetables,

especially citrus fruits. Vitamin C deficiency results in scurvy and its

associated symptoms. Extremely high amounts of more than 3,000 mg/day

of Vitamin C can result in diarrhea and GI disturbances

The RDA for adult males and females for Vitamin C is 90 mg/day and 75 mg/day, respectively.