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Vitamin E

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Structure

  • Phenlic functional group on a chromanol/chromane ring
  • Phytyl side chain (phytyl tail)
  • Tocopherols (free form)
    • Saturated side chain with 16 carbons
    • Alpha-tocopherol is the only form than can meet the body’s needs
  • Tocotrienols/trienols
    • Unsaturated 16 carbons

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Sources

  • Wheat germ
  • Nuts
  • Seeds
  • Vegetable oils
  • Spinach
  • Broccoli
  • Fortified cereals
  • Nut butter
  • Supplements (only 50% as active as form found in foods)
  • Destruction during food preparation and storage
    • Oxidization when exposed to air for long periods
    • Light and heat
    • milling

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Digestion/ Absorption

Digestion

  • Tocotrienols and synthetic tocopherols must be digested
  • Digested by pancreatic esterases functioning in the lumen or at the brush border membrane of the enterocyte

Absorption

  • Primarily in jejunum (20-70%)
    • Passive diffusion
  • Dietary lipids stimulate absorption
  • Bile salts needed for emulsification, solubilization, and micelle formation

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Transport

  • Chylomicrons transport through lymph into circulation
  • LDLs and HDLs primary carrier of vitamin in blood
    • Exchanged among lipoproteins to maintain plasma concentrations
  • Hepatic uptake follows delivery via chylomicron remnants

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Metabolism/ Excretion

Metabolism

  • Chylomicron remnants contain the different forms of vitamin E are taken up by liver
  • Liver only trafficks RRR-a-tocopherol for incorporation into nascent VLDLs
    • Uses aTTP
    • VLDLs released into blood

Excretion

  • Triglycerides on vitamin are removed by lipoprotein lipase
  • Almost all other forms excreted through bile

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Storage

  • Uptake into cells associated with lipoproteins via lipase-mediated hydrolysis
  • Once in cell binds to specific tocopherol-binding proteins for intracellular transport
    • Adipose tissue (primary storage site)
    • Liver, heart, muscle, adrenal glands, spleen, and brain

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Function

Antioxidant (main function)

  • Destroys singlet oxygen molecules
    • Readily react with proteins, lipids, and DNA
  • Neutralizes free radicals

Maintains integrity of membranes and lipoproteins

Cell-signaling molecule

  • Interacts with cell receptors

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Nutrient Interactions

  • Complimentary
    • Selenium
    • Vitamin C helps to regenerate vitamin E
    • Polyunsaturated Fat affects vitamin E requirement
  • Inhibited
    • B-carotene absorption and metabolism
    • Vitamin K absorption

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Possible Health Benefits

  • Decrease risk for heart disease
    • Inhibits oxidation of LDLs and platelet aggregation
    • Suppress release of inflammatory cytokines
  • Reduce risk for cancer
    • Reduces amount of free radicals in body
  • Improves eye health
    • Reduces risk of development of cataracts and age-related macular degeneration

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DRIs for Vitamin E

RDA

  • Men: 15 mg
  • Women: 15 mg
    • Pregnancy: 15 mg
    • Lactation: 19 mg

UL

  • 1,000 mg tocopherol
  • 1,100 IU synthetic tocopherol

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Deficiency

  • Serum levels <5 mg/L
  • Rare at risk groups include premature infants, individuals with cystic fibrosis, chronic cholestasis, and genetic defect in either lipoproteins or a-tocopherol transfer protein
  • Impacts integrity of cell membrance
    • Cell lysis
    • Hemolytic anemia
    • Degradation of nerve cells
  • Accumulation of ceroid pigments under the skin

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Toxicity

  • Serum levels >20 mg/L
  • Least toxic fat-soluble vitamin
  • UL establish for tendency of increased bleeding/impaired blood coagulation
  • Mild gastrointestinal problems
    • Nausea, diarrhea, and flatulence