Vitamin C/Ascorbic Acid

What is Vitamin C's role in Carnitine synthesis?

-Vitamin C keeps Fe in reduced state during hyroxylation reactions -Carnitine transports LCFAs from the cytoplasm into the mito

What are the 2 chronic diseases associated with vitamin C?

-Cancer: higher vit C intake and blood levels are associated with less risk. Stronger associations for cancers involving GI tract. Mechanism may involve stimulating immune cell function or blocking formation of carcinogens -CVD: Men with lowest C intakes have 75% greater risk. Suggested mechanism: vit C inhibits adherence of immune cells to vessel walls where they are oxidized

Food Sources of Vitamin C

-Fruits and veggies. Highest containing foods are kiwi, oranges, and strawberries. -Best if raw because Vit C is susceptible to cooking, processing, and storing. It is destroyed bu alkali, oxidation, and light. Storage with iron and copper also destroys Vit C -Can also be destroyed in water

What is Vitamin C's role as an antioxidant?

-Quenches free radicals by donating an electron to it. -Dehydroascorbic acid is transported into mito via GLUT 1 -Ascorbate accumulates in mito protecting it from ROS (radicals of oxygen)

Ascorbate Dietary Requirments

-RDA adults: Men: 90 mg/d Women: 75 mg/d Smokers: +35 mg/d due to oxidative damage -UL: 2 g/d >2 g/d leads to osmotic diarrhea and increased risk of kidney stones

What is Vitamin C's role in neurotransmitter synthesis?

-Regenerates a necessary cofactor that is needed for Tyr to be synthesized from Phe

What is Vitamin C's function in collagen synthesis?

-Required for hydroxylation reactions in collagen synthesis. Hydroxylation of proline and lysine enable collagen to cross-link and form a triple helix -Ascorbate acts to convert Fe+++ back to Fe++

What disorder is seen with a ascorbate deficiency? What are the signs?

-Scurvy. Total body pool of vitamin C <300 mg -Symptoms result from impaired hydroxylation of Pro Lys for collagen synthesis -Signs: Petechiae, brusing, arthralgia, loose and decaying teeth -Four Hs: Hemorrhage, Hyperkeratosis, Hyperchondriasis, and Hematologic

Vitamin C is essential for the maintenance of collagen and

-Skin -Cartilage -Tendons -Bone -Basement Membranes

Why do we need antioxidants?

-They attack phospholipid membranes, denature proteins, and destroy DNA. -Free radicals are generated by normal metabolism

How is Vitamin C absorbed?

-Through active transport across the lumen along small intestine in upper ileum (requires ATP) -Reduced form (ascorbic acid or ascorbate) is absorbed by energy-and sodium-dependent process -Oxidized form (dehydroascorbate) is transported by glucose (Glut 4) transporters -At average intake, absorption is 70-95% (higher absorption at lower intakes)

What is the metabolism of vitamin C?

-Upper limit to blood levels of 1.2 mg/dL -Beyond this, kidneys cannot reabsorb vitamin C and it is excreted in the urine -Liver and kidney oxidize ascorbate

Acorbate and Iron

-Vit C enhances intestinal absorption of iron, esp at C intakes of 27-50 mg/d -Ascorbate keeps Fe reduced -Prevents formation of insoluble iron complex -Acorbate may aid incorporation if iron into ferritin (the storage form of Fe)

4 Functions of Vitamin C

1. Collagen Synthesis 2. Carnitine Synthesis 3. Neurotransmitter Synthesis 4. Antioxidant *Many of these functions are based on ascorbate's ability to regenerate the reduced forms of Fe and Cu