Vitamin C and Biotin

Question 1

Vitamin C/ascorbic acid RDA

Answer 1

F - 75 mg/day
pregnancy - 100 mg/day
lactation - 120 mg/day
M - 90 mg/day
400-500 mg/day saturates body's vit c pool

smokers require 35 mg more

Question 2

Vitamin C/ascorbic acid absorption

Answer 2

easily absorbed in SI
transport proteins = down-regulated with excess
must slowly incr to achieve max dose
70-90% absorbed (30-180 mg/day)

Question 3

Vitamin C/ascorbic acid metabolism

Answer 3

diffusion from enterocyte to portal vein
free form in blood, no transport protein required
recycled/reduced by GSH
tissue concentrations = higher than plasma (80x higher in WBCs)
highest concentration = 
- adrenals 
- pituitary
- eyes
- brain

Question 4

Vitamin C/ascorbic acid functions

Answer 4

collagen synthesis
neurotransmitter synthesis: DA, 5HTP, NE
antioxidant
carnitine synthesis
enhances non-heme iron absorption
stabilizes WBCs/antihistamine effect

Question 5

Vitamin C/ascorbic acid: collagen synthesis

Answer 5

maintains skin, tendons, cartilage, bone, dentin, capillaries
cross-links proteins with hydroxyproline

Question 6

Vitamin C/ascorbic acid: antioxidant activity

Answer 6

reducing agent - donates e- to minimize free radicals
recycles oxidized vitamin E
protects DNA and PUFAs

Question 7

Vitamin C/ascorbic acid: enhanced iron absorption

Answer 7

reduces ferric to ferrous iron (more easily absorbed)

max benefits = 75 mg

Question 8

Vitamin C/ascorbic acid excess

Answer 8

> 2 g/day
nausea
diarrhea
incr risk of kidney stones (causes precipitation of oxalates)

Question 9

Vitamin C/ascorbic acid deficiency

Answer 9

scurvy
fatigue
delayed wound healing

Question 10

Scurvy

Answer 10

Hemorrhagic signs: easy bruising, petechiae
Hyperkeratosis of hair follicles
Hypochondriasis: cognitive impairment
Hematological abnormalities: iron malabsorption and impaired copper/iron metabolism

give 100-300 mg/day until resolved

Question 11

Vitamin C assessment

Answer 11

reduced intake 
malnourished/malabsorption/cachexia
incr alcohol use
tobacco use
elderly

Question 12

Vitamin C/ascorbic acid food sources

Answer 12

bell peppers
citrus
berries
brassicas
tomatoes
potatoes

Question 13

Vitamin C/ascorbic acid availability

Answer 13

destroyed by heat, oxygen, light

Question 14

Vitamin C/ascorbic acid supplements

Answer 14

natural = identical to synthetic
mineral ascorbates (ca ascorbate) may be gentler on stomach

Question 15

Biotin

Answer 15

produced by gut bacteria
absorption rate unknown, happens in proximal and mid-transverse colon
RDA = 30 mcg/day

Question 16

Biotin absorption

Answer 16

bound to biocytin (lysine residue) in food
requires biotinidase (from pancreas) to break amide bond
almost 100% absorbed in proximal SI (inhibited by alcohol)

Question 17

Biotin functions

Answer 17

Enzyme cofactor - esp carboxylase enzymes
- FA synthesis/oxidation
- Gluconeogensis: catabolism of BCAA, threonine, and methionine
Gene expression
- histone modification: causes uncoiling to allow activation
- DNA repair, gene replication, regulation, cell cycle regulation

Question 18

Biotin metabolism

Answer 18

can be recycled, so deficiency = rare

incr demand during pregnancy/lactation, tobacco use, anticonvulsant meds

Question 19

Biotin deficiency

Answer 19

= rare
hair loss
brittle nails
seborrheic dermatitis
paresthesia

Question 20

Biotin food sources

Answer 20

liver
eggs, cooked
avocado
salmon
almonds
legumes
pork