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28 terms

NTD412 - Antioxidants - Vitamin C

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another name for vitamin c
ascorbic acid
structure
C6H8O6, the only essential carbohydrate
sources: endogenous?
humans lack the enzyme (gulonolactone oxidase) to synthesize it but some animals can
best food sources
green veggies (asparagus, broccoli, brussels sprouts, etc.), citrus fruits (oj, grapefruit, cantaloupe), strawberries, potatoes
what can destroy vitamin c in foods?
heat, oxygen, high pH
digestion
no steps are required
absorption (location, mechanism)
small intestine, sodium dependent active transport (passive diffusion in stomach + small intestine at high intakes; dehydroascorbate via facilitated diffusion)
absorption: inhibitors
high intracellular glucose, high concurrent intakes of iron
transport
into plasma in free form (ascorbate anion); cellular uptake requires sodium and a carrier and sometimes energy
storage
highest concentrations in adrenal & pituitary glands (also: liver, spleen, heart, kidneys, lungs, pancreas, leukocytes)
two main functions
antioxidant, collagen synthesis
other functions
carnitine synthesis; tyrosine synthesis & catabolism, neurotransmitter synthesis, microsomal metabolism
functions: collagen synthesis
after collagen chains are made, vitamin C helps cross-link it into its helix configuration via the hydroxylation of proline and lysine
functions: antioxidant activity
related to its general capacity as a reducing agent/electron donor in aqueous solutions: (1) regenerates other antioxidants (2) reduces free radicals before they can damage cells, becomes oxidized in the process + must be regenerated
free radicals
molecules with 1 unpaired electron that attakcs nucleic acids in DNA, PUFA in phospholipids, and proteins in cells; can be cancerous (DNA)
functions: cold prevention?
mostly refuted, may weakly help
functions: cancer prevention?
possibly of GI tract (oral cavity, pharynx, esophagus, stomach); possible mechanisms: immunocompetence, antioxidant, ability to detoxify carcinogens/block carcinogenic processes
functions: cardiovascular disease prevention?
low vitamin C status may increase blood total cholesterol; high status may decrease blood pressure and increase HDL
functions: cataracts prevention?
cataracts result partly from oxidative damage to proteins in the eye's lens, so it works as an antioxidant
interactions with other nutrients
enhances nonheme intestinal absorption by reducing ferrous to ferric; decreases serum copper and ceruloplasmin but may inhibit binding to metallothionein
excretion
intact or oxidized to dehydroascorbate in the liver or kidneys; mostly excreted in urine; renal absorption threshold = 1.2mg/dL
when does the RDA increase?
pregnancy, lactation, smoking status
deficiency results in _____ when ____
scurvy, total body vitamin C pools < 300mg and plasma vitamin C concentrations <.2mg/dL
signs & symptoms of deficiency
tend to result from impaired hydroxyproline and hydroxylysine synthesis for collagen: bleeding gums, hemorrhages, easy bruising, impaired wound + fracture healing, joint pain, loose/decaying teeth, hyperkeratosis of hair follicles
deficiency: populations at risk
elderly, alcoholics, drug abusers, people on poor diets (esp. infants from poor SES), people with diabetes and some cancers
toxicity side effects
abdominal pain/nausea/vomiting, osmotic diarrhea, increased risk of kidney stones due to metabolism into oxalate, iron toxicity
UL?
2g
assessment of nutriture
plasma and serum concentrations respond to changes in dietary vitamin C intakes so it's a good measure of recent intake