Vitamin C

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Vitamin C
2013-02-11 09:08:52

Nutr 620 vitamin C
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  1. 1. Who can make vit C? from what pathway? (write substrate, metabolite, and product)

    2. As dosage increases, how does bioavailability change? What happens if you take too much Vitamin C?

    How is vitamin C status assessed?
    1. Most animals (except us, guinea pigs, birds, bats, most fish) from glucose and all plants from glucose --> glucuronic acid --> vitamin C

    2. As dosage increases, bioavailability decreases (at normal levels, almost totally used, at high doses 1000 mg - only 50% absorbed)

    Osmotic diarrhea (not absorbed), chewable tablets can harm teeth.

    Via plasma vitamin C levels
  2. What is vitamin C's most important function?

    What are the two forms of Vitamin C? Which is the oxidized and which is the reduced version?

    • Ascorbic = reduced form; DHA = oxidized form
  3. What are 5 functions of Vitamin C?
    • 1. Antioxidant
    • 2. Important for collagen formation (bones, muscle, tissues, healthy gums)
    • 3. Wound healing (collagen)
    • 4. Fighting infections
    • 5. Prevention of heart disease and cancer
  4. 1. What form of vitamin C is most commonly found in nature?
    2. Does breast milk have vitamin C?
    3. Is cooking best or raw sources for vitamin C?
    4. What are some conditions (3) or drugs (4) that deplete vitamin C levels?
    • 1. Ascorbic acid (~80-90%)
    • 2. Yes.
    • 3. Raw, since cooking destroys vitamin C's structure
    • 4. Conditions (high stress, smoking, diabetes) drugs (birth control, alcohol, analgesics, steroids)
  5. 1. Where does absorption occur?
    2. What transporter is needed? (2) With what ion?
    3. How does it get from enterocytes into plasma?
    4. What is its transported form? What binding protein is used?
    5. What happens once DHA is absorbed?
    • 1. Jejunum and ileum
    • 2. SVCT or GLUT 1,3 or 4. SVCT requires Na+ (dominant Vitamin C transport in body)
    • 3. Unknown
    • 4. Ascorbic acid = transported form. None
    • 5. Once DHA is absorbed, it's quickly reduced to ascorbic acid.
  6. 1. How is ascorbic acid turned into DHA? (substrate, intermediate, product)
    1. Oxidation via two successive losses of a single electron (Ascorbate, ascorbyl radical, DHA)
  7. What rxns is vitamin C important for? 5
    • 1. Reduction of free H2O2 (DHA & GSH), NADPH and NADP+
    • 2. Collagen synthesis (post-translational hydroxylation of proline and lysine residues - necessary for cross-linked increasing tensile strength of fiber)
    • 3. Carnitine biosyntehesis
    • 3. Norepinephrine synthesis
    • 5. Also increases bioavailability of nonheme iron from plants (Fe3+-->Fe2+ --> better absorbed)
    • - Also enhances translation of ferritin mRNA into protein to store iron in tissue.

  8. How does Vitamin C affect iron levels in body? 2
    Increases them by

    (1) increasing absorption: enhancing bioavailability and absorption of nonheme iron from plants (Fe3+-->Fe2+)

    (2) Increases storage by increasing mRNA translation of ferritin (iron storage)
  9. How does vitamin C affect collagen synthesis? What enzymes are used?
    It's integral for collagen synthesis.

    It is involved in post-translational hydroxylation of proline and lysine residues on collagen that are integral for cross-linking in triple helix structure.

    Cross-linking is required for tensile strength of collagen fiber

    Enzymes: Prolyl and lysyl hydroxylases require vitamin C as a cofactor
  10. What are causes of vitamin C? 4
    Rare in developed world- inadequate intake and severe malabsorption (cancer/kidney disease, smokers), conditions where demand > intake (smokers, diabetics, stress)
  11. When would you get scurvy?
    What are some symptoms? (9)

    Can scurvy be fatal?

    How soon after vitamin C therapy are improvements seen in scurvy?
    1. Below <10 mg/day; 45-80 days after vitamin C intake.

    2. Weight loss, fatigue, connective tissue weakness, joint pain, hyperkeratosis, slow healing of wounds, fragile capillaries, iron deficiency anemia, reduced resistance to colds

    One week
  12. Who is susceptible to vitamin C inadequacy? 4
    • 1. Smokers
    • 2. Those with limited food access (elderly, children, food faddists, drug addicts)
    • 3. Those with malabsorption
    • 4. Stressed out people
  13. 1. Does vitamin C increase risk of kidney stones?
    2. Does it treat/cure cancer?
    3. How does Vitamin C affect duration & severity of cold?
    • 1. No
    • 2. No
    • 3. Only if host status is compromised (soldiers, marathon runners, etc) - helps prevent cold. Otherwise, only decreases duration, not severity as long as its taken before onset of cold.
  14. What are levels of deficiency, normal intake and toxicity? What symptoms are associated with each?
    Deficient (0 mg/day) - scurvy, anemia, fatigue, hyperkeratosis, dry hair/skin, joint pain

    Normal - 15-90 mg/day Normal connective tissues, immunity, non-heme Fe absorption

    Toxicity > 2000 mg/day, mild laxative, stomach upset, erosion of enamel