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Fat Soluble Vitamins
Barnali Deori
M.Sc.1st yr
Deptt. of Food and Nutrition
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Fat Soluble Vitamins (A, D, E, K)
Soluble in lipids and solvents
Found in the fats and oils of food.
Excess stored and not excreted.
Absorbed into the lymph and carried in blood with protein
transporters - chylomicrons.
Stored in liver and body fat and can become toxic if large amountsare consumed.
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Vitamin A
3 forms: retinol ( transport and storage form of vitamin A ),
retinal (essential for vision), retinoic acid (acts like a hormone)
precursor beta carotene
Roles in body:
Regulation of gene expression
Part of the visual pigment rhodopsin, maintains clarity of
cornea.
Required for cell growth and division - epithelial cells, bones
and teeth
Promotes development of immune cells, especially
Natural Killer Cells
Antioxidant
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Vitamin A- Structure
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Metabolism
Absorption and Bioavailability
Seventy to ninety percent of vitamin A from the diet is absorbed in
the intestine
Greater than 90% of the retinol store within the body enters as
retinyl esters that are subsequently found within the lipid portion of
the chylomicron
Absorption of vitamin A is very rapid, with maximum absorption
occurring two to six hours after digestion.
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Within the intestinal lumen the vitamin is incorporated
into a micelle and absorbed across the brush border intothe enterocytes.
Within the enterocyte, precursors of vitamin A
(carotenoids) are converted to active forms of the
vitamin.
The newly formed products and additional precursors
are then packaged into chylomicrons and readied for
transport throughout the body.
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Transport
After leaving the enterocytes, chylomicrons, which carry retinyl
esters, carotenoids, and unesterfired retinol along with triglycerides,
are circulated first through the lymphatic system and then through
the general circulation.
The vitamin A is then incorporated into a chylomicron remnant. The
chylomicron remnant then travels back to the liver where it is taken
up and further metabolized or stored.
Retinol-binding protein (RBP) is the specific carrier used to transportall-trans retinol in the plasma. This specific carrier is manufactured
and secreted by the parenchymal cells of the liver.
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Each mole of retinol released binds with RBP to form
holo-RBP. This compound then binds with a molecule of
transthyretin (TTR), formerly known as prealbumin.
This newly formed retinol-RBP-TTR complex is notfiltered by the glomerulus, but instead freely circulates
throughout the plasma.
Tissues are then able to take the retinol up as needed
via cellular retinoid-binding protein.
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Storage
Approximately 50 to 85% of the total body retinol are stored in the liverwhen vitamin A status is adequate.
Retinol returning to the liver is re-esterfied before storage. Because of
this, over 90% of the retinol is stored in the form of retinyl esters.
The retinol is stored in hepatic stellate (star-shaped) cells along with
droplets of lipid.
The size of stellate cells increase linearly with increasing retinol levels.
Once hepatic stellate cells are saturated with all the retinol they can
hold, hypervitaminosis can result.
The precursor to vitamin A, beta-carotene, can be stored in
adipose cells of fat depots throughout the body.
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Vitamin A is very important for immune system of
the human body.
Skin, lining the digestive and urinary tracks, contains Retinol. This
lining restricts the entrance of various infectious microbes and other
harmful materials.
Retinoic acid and vitamin A are also essential for the formation of
white blood cells, which are very important for fighting different
infectious materials, hence strengthening the immune system.
Different studies suggest that Vitamin A is helpful in reducing growthof cancer in different parts of human body for example liver, breast,
colon and skin.
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Deficiencies cause: Night blindness, xerophthalmia (keratin deposits in cornea),
macular degeneration.
Skin and mucous membrane dryness and infection, keratindeposits.
Anemia
Developmental defects bones, teeth, immune system,vision.
Toxicities (single large doses of supplements, eatingexcessive amounts of liver) cause:
Fragile RBCs, hemorrhage
Bone pain, fractures
Abdominal pain and diarrhea
Blurred vision
Dry skin, hair loss
Liver enlargement
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Vitamin D
There are two main forms of dietary Vitamin D, those are
D2 (ergocalciferol) and
D3 (cholecalciferol).
D2 is mainly produced by plants, and is not as bioactive inhumans as the D3 form.
There are three forms of vitamin D that function in the body.
Cholecalciferol (vitamin D3). This is the form of the vitaminmade in the skin.
Calcidiol (25-hydroxyvitamin D). The storage form of thevitamin in human tissues.
Calcitriol (1,25-hydroxyvitamin D). The active, steroid form,of vitamin D
precursor is cholesterol,
It is the only fat soluble vitamin that we can make- in the presenceof sunlight.
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Vitamin D- Structure
Vitamin D3 (Cholecalciferol)Vitamin D2 (Ergocalciferol)
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Absorption of Vitamin D
80% of vitamin D consumed is incorporated into
micelles.
Bile salts are essential for its absorption.
After combining with bile salts, it passes into the lacteal
system through the intestinal epithelial cells.
Absorption occurs from duodenum and jejunum through
the lymphatic system and transported via
chylomicrons and passes into the blood
stream.
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Vitamin D3 derived from dietary sources is transported by a specific
vitamin D-binding protein, to liver where it is further metabolised to
25-hydroxy vitamin D3.
25-hydroxy vitamin D3 is further metabolised to 1,25 dihydroxy
vitamin D3 in the kidney.
1,25 dihydroxy vitamin D3 is the active hormonal form of vitamin D
which brings about all the biological functions of the body.
EXCRETION
Excreted in bile
Metabolized to water soluble metabolites and then
excreted in urine as well.
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Vitamin D- A Vitamin or a Hormone
Vitamin D is not really a vitamin at all - it is a pre-
hormone that's produced in the skin in response to
sunlight exposure. As such, it is an integral part of
human health and longevity.
It functions as a steroid hormone. What steroid
hormones do is go in to the nucleus of cells, and alter
gene expression, that is turning genes on or off, or
simply giving them a nudge in either direction.
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FUNCTIONS
Immunity
The inactive form of vitamin D aids in the formation of activevitamin D which enhances immunity and inhibits the development
of autoimmune disease.
Calcium balance
With decreased dietary calcium, PTH is secreted and causes
increased production of calcitriol, a hormone
Calcitriol restores normal calcium levels by increased absorption
of dietary calcium, increased mobilization of calcium from bone,
and increased reabsorption from kidneys
Heart disease
Renin, important in regulation of blood pressure
and heart health, is associated with vitamin D levels.
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Vitamin D: Deficiency Rickets (children)
bone deformities in children
Osteomalacia (adults)
weak bones due to low calcium content
Vitamin D deficiency
Calcium deficiency multiple pregnancies
Toxicities Loss of calcium from bone and deposition in soft
tissues.
Loss of appetite, nausea and vomiting,
psychological depression.
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Vitamin E
The name Vitamin E covers a collection of eight fat soluble
compounds, tocopherols and tocotrienols:
alpha-Tocopherol - the most common and biologically active
beta-Tocopherol
gamma-Tocopherol
delta-Tocopherol
alpha-Tocotrienol
beta-Tocotrienol
gamma-Tocotrienol
delta-Tocotrienol
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All have a 6-chromonal ring structure and a side chain.
The tocopherols have a completely saturated hydrocarbon chain,
whereas the tocotrienols are characterized by a partly unsaturatedhydrocarbon chain.
Other tocopherol and tocotrienol compounds differ in the number
and position of methyl groups attached to the chromanol ring.
The hexagonal component on the left side of each structure holdsthe antioxidant activity of the vitamin E structure.
The human genome has selected alpha-tocopherol among these 8
compounds and has evolved a number of specific proteins to protect
it and distribute it throughout the body. The major distinction
between them and alpha-tocopherol, however, is the speed with
which they are cleared from your system.
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Vitamin E- Structure
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Metabolism
Absorption and Bioavaliability
Absorption of vitamin E is highly dependent upon the same
processes that are utilized during fatty acid digestion and
metabolism.
Bile acids are considered essential for vitamin E absorption andmicelle formation.
Once formed, the micelle is then able to cross the unstirred water
layer and release its contents into the enterocyte.
After passing through the enterocyte the vitamin E is
packaged into a chylomicron and readied for circulation.
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Transport
The vitamin E in the chylomicron equilibrates with both High-Density
Lipoproteins (HDL) and Low-Density Lipoproteins (LDL). From the
HDL all circulating lipoproteians eventually receive vitamin E.
The vitamin E remaining in the chylomicron becomes a chylomicron
remnant and travels back to the liver for re-uptake.
Once in the liver, the vitamin E is packaged into Very Low Density
Lipoproteins (VLDL) and excreted back into the circulation. The
predominant transfer of the alpha vitamin is performed by alpha
tocopherol transfer protein (ATTP).
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As the VLDL are broken down by lipoprotein lipase, LowDensity Lipoproteins (LDL) are formed and from these
lipoproteins the vitamin E is transferred to HDL and
eventually incorporated into peripheral tissue.
A final mechanism for vitamin E is uptake by the
peripheral tissue from the chylomicron via lipoprotein
lipase activity.
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Storage
Vitamin E is a lipid soluble vitamin and therefore over
90% of total body vitamin E is found in the adiposetissue.
Excretion Vitamin E is excreted mainly via bile, urine, feces, and
the skin.
Because of the poor intestinal absorption of vitamin E,
fecal excretion is the main route of vitamin E
elimination.
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How do other nutrients interact with vitamin E?
The recycling of vitamin E in the body is intricately connected to four
other nutrients: vitamin C, glutathione, selenium, and vitamin B3.
Vitamin C is required to keep vitamin E in its metabolically active
form;
glutathione (a very small protein molecule called a tripeptide and
consisting of three amino acid building blocks) is required to keepvitamin C in its active form;
selenium (a micromineral) and vitamin B3 are required to keep
glutathione in its active form.
The fact that vitamin E is so heavily dependent on vitamin C,
vitamin B3, selenium, and glutathione means that a diet
high in vitamin E cannot have its optimal effect unless it
is also rich in foods that provide these other nutrients.
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What are Free Radicals?
It is ironic that oxygen, which is an indispensable
element for life can have severe deleterious effects on
the human body under certain situations.
Most of the potentially harmful effects of the oxygen aredue to the formation and activity of number of chemical
compounds, known as reactive oxygen species (ROS),
which have tendency to donate oxygen to othersubstances.
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Many such reactive species are free radicals.
When the mitochondria of the cells produce energy, they throw off
molecules called free radicals in the process.
Free radicals are those molecules which have a surplus of one or
more free floating electrons in its outer ring rather then having
matched pairs and are therefore, unstable and highly reactive.
Types of free radicals
Hydroperoxyl radical
Superoxide radical
Hydrogen peroxide
Triplet oxygen
Singlet oxygen
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Sources of free radical
Free radicals and other reactive species are derived either from
normal essential metabolic processes like enzymatic reactions
(those involved in the respiratory chain, in phagocytosis, in
prostaglandin synthesis, etc.) or from external sources, such as
exposure to x-rays, ozone, cigarette smoking, air pollutants,
industrial chemicals etc.
Mental status like stress, emotion etc. and disease conditions are
also responsible for the formation of free radicals.
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How are free radicals formed in the humanbody?
Free radicals are produced in most cells of the body as a byproduct
of metabolism, although some cell types manufacture larger
quantities for specific purposes.
These free radicals are always in search of stabilizing themselves
by undergoing chemical reaction with other atoms and molecules.
They rob other atoms of their electrons in order to stabilize
themselves and in this way oxidation reaction takes place
and thus cause cell death and injury.
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When free radicals steal an electron from a surrounding compound
or molecule a new free radical is formed in its place. In turn, the
newly formed radical then looks to return to its ground state by
stealing electrons from cellular structures or molecules. Thus the
chain reaction continues and can be "thousand of events long."
If free radicals are not inactivated, their chemical reactivity can
damage all cellular macromolecules including proteins,
carbohydrates, lipids and nucleic acids.
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Mechanism for the formation of freeradicals
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Vitamin E and heart disease -
Vitamin E helps protect against heart disease by limiting the
oxidation of LDL-cholesterol.
Vitamin E also keeps arteries flexible and elastic, allowing blood to
flow freely.
Vitamin E helps prevent arteries from clogging by blocking the
conversion of cholesterol into the waxy fat deposits called plaque
that stick to blood vessel walls.
Vitamin E also thins the blood, allowing for blood to flow more easily
through arteries even when plaque is present.
Vitamin E also may help prevent the formation of blood clots, which
could lead to a heart attack.
Vitamin C and vitamin E, taken in combination, help to
stabilise LDL cholesterol in the body. This may help
to reduce the risk of atherosclerosis
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Vitamin E and cancer -
Some cancers are believed to result from oxidative damage to DNA
caused by free radicals. Free radicals can damage DNA, leading tomutations in cells that may cause cancer.
Antioxidants such as vitamin E help protect against the damaging
effects of free radicals. Vitamin E may protect against the
development of cancers by enhancing immune function.
Some evidence associates higher intake of vitamin E with a
decreased incidence of prostate cancer and breast cancer.
Cigarette smokers have a higher risk of developing cancers of the
mouth, upper airways and lungs, and vitamin E may help
protect smokers against these cancers through
its antioxidant properties.
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Vitamin E and alzheimer's disease -
Alzheimer's disease is a wasting disease of the brain.
Oxidative stress is believed to contribute to the development of
Alzheimer's disease. Vitamin E is an antioxidant that prevents free
radical damage in biological membranes.
Vitamin E supplementation improves cognitive performance in
healthy individuals.
In addition, vitamin E, together with vitamin C may prevent thedevelopment of Alzheimer's disease.
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Recommended daily allowance (RDA)
The recommended dietary allowance (RDA) for vitamin E is
10 mg/day for the adult man,
8 mg/day for the adult woman, and
3 mg/day for the infant.
In April 2000 the Food and Nutrition Board raised the RDA for men
by 50 percent and nearly doubled the RDA for women. The new
RDA is 15 milligrams for both sexes, including pregnant women. For
lactating mothers it is 19 milligrams.
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Sources of vitamin E
Vitamin E is found in the germ of a seed or grain.
The best sources of vitamin E are vegetable oils such
as sunflower, canola, corn, soybean and olive oil and
products made from these oils (such as margarine).
Nuts, sunflower seeds and wheat germ are also good
sources.
Other sources of vitamin E are whole grains, fish, peanut
butter, and green, leafy vegetables.
In these oils, approximately 50 percent of the tocopherol
content is in the form of alpha-tocopherol.
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Deficiencies
Vitamin E deficiency affects the central nervous system and
may result in progressive neuromuscular disease
characterized by loss of reflexes, muscle weakness, loss ofbalance and impaired ability to coordinate voluntary
movements (ataxia).
Vitamin E deficiency may also contribute to cardiovascular
diseases, including atherosclerosis, as well as an increased
risk of certain cancers.
Premature infants may be at risk for vitamin E deficiency
because they may be born with low tissue levels of the
vitamin, and because they have a poorly developed capacity
for absorbing dietary fats.
Toxicities (more than 1000 milligrams/day)
Interfere with the body's ability to clot blood.
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Vitamin K3 forms:
Phylloquinone (K1, which naturally occurs in plants ),
menaquinones (K2, which is produced by the bacteria that lines
gastrointestinal tract ) and
menadion (K3, a synthetic form of vitamin K, which is converted tovitamin K2 in the intestine ).
The Menaquinones differ from Phylloquinones in the number of
isoprene units in the side chain.
Vit i K St t
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Vitamin K- Structure
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Metabolism
Absorption and transport Dietary vitamin K, mainly as phylloquinone, is absorbed in the small
intestine and the process is facilitated by bile salts and pancreatic
juices.
Within the intestinal mucosa the vitamin is incorporated intochylomicrons, is secreted into the lymph, and enters the blood via
the lacteals.
Phylloquinone is the major circulating form of vitamin K but
menaquinone is present in plasma at lower concentrations and has
a lipoprotein distribution similar to phylloquinone.
Menaquinones are synthesized by the bacteria in
the colon and are absorbed.
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Tissue stores and distribution
Human liver stores normally comprise about 90 percentmenaquinones and 10 percent phylloquinone.
Other sites of storage may be adipose tissue and bone; both are
known to be sites where vitamin K-bearing chylomicrons and
chylomicron remnants may be taken up.
Excretion
Vitamin K is extensively metabolised in the liver and excreted in the
urine and bile.
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Functions of vitamin K
Promotes healthy blood clotting
Vitamin K is used by the liver to form at least four different kinds of
proteins that are necessary for blood to properly clot. These factors
include prothrombin, proconvertin, thromboplastin component, and
Stuart factor.
Other clotting factors that depend on vitamin K are protein C, protein
S, and protein Z.
Deficiency of vitamin K or disturbances of liver function may lead to
deficiencies of clotting factors and excess bleeding. Vitamin K1 is the preferred form used in the liver to
carboxylate clotting factors.
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Protects bones from weakening or fracture
Vitamin K is responsible for assisting in the formation of three
important proteins produced outside the liver. These proteins are
osteocalcin, matrix Gla protein, and protein S.
Osteocalcin is involved in the mineralization of bone. Adequate
vitamin K intake and vitamin K body levels are linked to bone
mineral density.
Research found that patients who suffered fractures caused by
osteoporosis had vitamin K levels 70% lower than age-matched
controls.
Vitamin K2 also works with vitamin D3 to increase the production of
Gla-proteins, including osteocalcin in osteoblasts (the cells that buildbone), while also inhibiting the production of osteoclasts
(the cells that break down bone).
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Prevents calcification of blood vessels
or heart valves
One common problem in many forms of cardiovascular disease
is unwanted calcification, the build-up of calcium inside a
tissue that is normally soft. This build-up of calcium causes the
tissue to harden and stop functioning properly
One direct way to inhibit the build-up of calcium along thearteries is to maintain ample supplies of a special protein called
MGP in the body.
MGP, or matrix Gla protein, directly blocks the formation of
calcium crystals inside the blood vessels. For MGP to function in this way, it must first be present in its
carboxylated form; vitamin K is required for this
carboxylation process.
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Deficiencies
Deficiencies are rare but seen in infants, after prolonged antibiotic
therapy, and in patients with decreased bile production.
Infants are at higher risk for hemorrhagic disease of newborn,
caused by a lack of Vitamin K reaching the fetus across the
placenta, the low level of Vitamin K in breast milk, and low colonicbacterial synthesis.
In adults, Vitamin K deficiency is uncommon due to the intake of a
wide variety of vegetables and other foods; the recycling ability of
Vitamin K , which helps to conserve the body's supply; and
adequate gut flora to produce Vitamin K.
F d Th C i Vi i K
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Foods That Contain Vitamin K
Green leafy vegetables as the richest sources of vitamin K.
Examples include kale, spinach, turnip greens, parsley, mustardgreens, broccoli and leaf, lettuces. Other vegetable sources for
vitamin K include cauliflower, green beans, coriander and okra.
Fruits like kiwi, blackberries, blueberries and red grapes are also
good sources of vitamin K. Some meats contain vitamin K, including dark turkey meat, chicken
meat and cow liver. Egg yolks and mayonnaise, which contains
eggs, also contain vitamin K. Dairy sources of vitamin K include
yogurt, butter and some cheeses. Oats, wheat and rye contain vitamin K.
Similar food sources of vitamin K include safflower oil, olive oil,
canola oil, soybeans, soybean oil and fermented soybean products.
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Recommended Dietary Allowances
RDA for adult males: 80 mcg
RDA for adult females: 65 mcg
RDA for children 7 to 10 years: 30 mcg
RDA for infants: 10 mcg
RDA for pregnant and lactating women 65 mcg
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