Vitamin C Flashcards
What are the two chemical forms of Vitamin C? How do they differ in their function?
- Ascorbic Acid (AA)
-protects against oxidative damage by donating 2H to radicals - Dehydroascorbic Acid (DHAA)
-accepts H to become AA again
-needed for Vit C antioxidant activity
What is the precursor for Vitamin C synthesis in nature?
D-glucose
-synthesizeed by plants / animals
-humans lack enzyme required to make AA
How is Vit C absorbed? how effective is this?
primarily absorbed by active transport
-saturable + dose-dependent
-80-90% bioavailible up to 100mg
DHAA is absorbed by facilitative transport and is less bioavailable
-GLUT 1/3/4
How is Vit C transported?
transported in plasma as ascorbic acid
Where is Vit C stored in the body? how much is stored/ what is its half life?
stored in tissues with active metabolism
-half life ~20 days (1500mg storage)
What are the two transporters involved in Vitamin C absorption? where do each of them function?
- SVCT1: organs that maintain homeostasis (kidney, intestine, skin, lungs)
-dietary absorption / renal reabsorption - SVCT2: vital organs (heart,brain, eyes, muscle, adrenals)
-metabolically active and specialized tissues
What happens to DHAA if it is not reduced back to AA?
It is further oxidized to 2,3-diketogulonic acid which can be cleaved into oxalic acid + sugar
What are the main urinary excretion products of Vitamin C?
- Dehydroascorbate
- Diketogulonic acid
- Oxalic acid
- Excess ascorbate
what is Vit C filtration and absorption dependent on? what is the issue with excess levels of Vit C?
plasma [vit C]
body pool > 1500mg increases AA in urine
-excess levels can mask clinical tests, such as urinary glucose
what are enzymatic functions of Vit C?
electron dontation
-monoxygenases
-dioxygenases
what are non-enzymatic functions of Vit C?
1) antioxidant
2) Fe absorption
3) Tetrahydrobiopterin recycling
How is Vit C involved in a monoxygenase?
AA is needed in order to reduce Cu2+ back to Cu+
Cu+ is needed for the conversion of dopamine to generate norepinephrine
What is the role of Vitamin C in collagen synthesis? why is collagen important?
It is required for hydroxylation of proline and lysine (needed to reduce Fe3+ to Fe2+ to be used in the rxn)
-stimulates proper folding and structural stability of collagen
collagen is important for extracellular matrix, bone cartilage, scar tissue, smooth muscle cells
what types of reactive species do antioxidants work on?
ROS, nitrogen species, sulfur species, antioxidant radicals
how does Vit C maintain antioxidant status?
It is able to be regenerated by glutathione to act as an antioxidant
It works to donate H to radicals
How do antioxidants work synergistically?
The various antioxidants work together to reduce/oxidize each other in order to deal with radicals and reactive species
How does Vit C enhance Fe absorption?
It reduces dietary Fe3+ to Fe2+(more bioavailable form and can be more easily absorbed)
Why is the recyling of tetrahydrobiopterin using Vit C important?
Tetrahydrobiopterin (BH4) is needed in the production of Ep, Nep an d dopamine
What are the symptoms of scurvy?
- Fatigue and Weakness
- Anemia
- Bleeding Gums
- Joint and Muscle Pain
- Slow Wound Healing
what are the 4H’s? when do they occur?
what is the RDA for Vit C for men/women? What is the upper limit (UL)?
Men: 90mg
Women: 75mg
2000 mg/day
What are rich food sources of Vitamin C? how stable is Vit C in food?
- Red bell peppers
- Kiwi
- Oranges
- Broccoli
- Tomatoes
-Destroyed by heat, light, oxidation and alkaline solutions
-Stable in acidic environments
What is a potential consequence of high doses of Vitamin C? when would this occur?
Increased Fe absorption, pro-oxidant activity (reaction of AA with other molecules to become a radical), interferance of clinical tests and kidney stone intake with several large doses (> 1000mg)
What chronic disease risk can Vitamin C help reduce?
*Coronary heart disease
*CVD
-reduced plaque formation due to role in NO production
* Cancer
* stroke
-can reduce all cause mortality risks
