Vitamin C

Question 1

Vitamin C functions

Answer 1

cofactor in enzyme reactions
dioxygenases: collagen synthesis
Lysine–> Hydroxylysine (OHLys)
and proline –> hydroxyproline (OHPro)

Question 2

collagen function

Answer 2

strength for connective tissue and bone from hydroxylysine and hydroxyproline cross-link

Question 3

dioxygenases and ascorbic acid and iron

Answer 3

dioxygenases have iron
Fe+2 -> Fe+3

ascorbic acid converts Fe+3 -> Fe+2 so dioxygenase remains active

Question 4

How does C act as an antioxidant

Answer 4

ascorbic acid (AH2) <-> dehydroascorbic acid (A) *lost 2 H, proton and electron)

Question 5

ascorbic acid and dehydroascorbic acid chemical formulas

Answer 5

ascorbic acid: C6H8O6 = reduced
dehydro: C6H6O6 = oxidized

Question 6

2 steps of ascorbic acid to dehydro

Answer 6

1. AH2 -> AH RADICAL + (e-) + (+)
2. AH RADICAL + (e-) + (+) -> A + (e-) + (H+)
   *AH RADICAL is semidehydroascorbic acid radical = ascorbyl radical
   vitamin C donates 2H atoms (2e- and 2H+) in antioxidant reaction

Question 7

ROS molecules function

Answer 7

unpaired e-
react (take electron) other molecules, it becomes nonradical but leaves behind a radical (lipid, protein, DNA radicals)

Question 8

direct action of antioxidant mechanism

Answer 8

AH2 + H202 -> A + 2 H2Oo

donate 2H atoms to remove a ROS, no enzyme

Question 9

how to reduce Vit C back to AH2?

Answer 9

reduced glutathione (GSH) can regenerate C

A + 2GSH + -> AH2 + GSSG

Question 10

Vitamin C food sources

Answer 10

F&V
NOT: grains, meat, milk

*exception human breast milk= 45mg/L, raw organs

Question 11

Vitamin C RDA

Answer 11

men= 90mg
Women= 75mg

add 35mg if smoker

Question 12

Vitamin C EAR value and how it was set

Answer 12

= 75mg

(males) using near saturation of neutrophils with minimal urine excretion

decrease 20% for women

DRI is set for antioxidant function, not just prevent scurvy

Question 13

C deficiency/scurvy 4 Hs

Answer 13

1. Hemorrhagic: broken capillaries on skin (petechiae), bleeding gums
2. Hyperkeratosis: abnormal skin bumps (also A deficiency)
3. Hypochondria: psychological problems bc of less neurotransmitters
4. Hematologic abnormalities: poor Fe absorption

Question 14

Vitamin C UL

Answer 14

2g

based on occurrence of osmotic diarrhea

LOAEL= 3g

Uncertainty factor= 1.5, not high bc reversible

UL=LOAEL/UF = 3g/1.5= 2g

Question 15

Absorption % and transport type
1. intake 20-30mg
2. 120-180mg
3. 12g

Answer 15

1. 98%, all by active transport
2. 70%, most by active
3. 16%, most by passive

Question 16

assessment of Vit C status

Answer 16

plasma= transport in and out of pool stores
urine excretion of C= indirect measure of plasma
WBC level= amount in tissue where antioxidant activity is important