Vitamin C

Vitamin C, also known as ascorbate or ascorbic acid, is a well-known antioxidant. Vitamin C serves the ability to preserve food but is destroyed when oxidized, added to alkaline solutions, and exposed to heat and light.¹ Minerals iron and copper oxidize vitamin C; the oxidized version of vitamin C is called dehydroascorbic acid (DHA).¹ Vitamin C is found in high levels within the brain, eyes, white blood cells, etc.¹ ²

Absorption: Vitamin C and DHA is absorbed by passive diffusion or facilitated diffusion (only DHA).¹ DHA is converted quickly into vitamin C and absorbed using glucose transporters (GLUT 1-4), and vitamin C uses transporters sodium-ascorbate cotransporter 1 and 2 (SVCT1 and SVCT2).¹

Functions:  

Collagen Synthesis - The protein collagen, found in bones, cartilage, skin, etc, depends on vitamin C as a reductant for the cofactor iron in enzymes called prolyl and lysyl hydroxylases (also needing copper)  to crosslink collagen fibers.¹

Iron Absorption - Iron is absorbed better as reduced ferrous (Fe2+) iron rather than ferric (Fe3+), and vitamin C promotes ferrous iron.¹

Carnitine Synthesis- Similar to collagen synthesis, vitamin C is used as a reductant for cofactor iron in enzymes trimethyllysine hydroxylase and 4-butyrobetaine hydroxylase involved in carnitine synthesis.¹ Carnitine transports fatty acids for b-oxidation for energy synthesis.¹

Tyrosine Synthesis- Vitamin C is used to regenerate the substrate for the enzyme phenylalanine hydroxylase whose role is to convert amino acid phenylalanine into tyrosine. Tyrosine is converted to the neurotransmitter dopamine, and the conversion of dopamine (derived from tyrosine) to norepinephrine uses vitamin C as a reductant for copper in the adrenal glands.¹

Antioxidant Capacity - Vitamin C donates electrons to free radicals superoxide and hydroxyl radicals.

Other Roles - Vitamin C may also play a role in the release of adrenal gland hormones and promote vitamin E’s antioxidant capacity. 

Dietary Reference Intake (DRI) - The recommended dietary allowance (RDA) for adult men and women over 19 years old is 90 and 75 micrograms/day.² Smokers need 35 mcg/day more than non-smokers. 

Deficiency - Vitamin A deficiency is known to cause scurvy which results in hemorrhaging of gums and under skin (improper collagen synthesis) and bone/joint pain.

Toxicity - Rebound scurvy can develop with vitamin C toxicity due to the body’s ability to destroy excess vitamin C. Chronic, excess vitamin C from supplementation can result in intestinal damage and hemolytic reactions.¹ Hypervitaminosis symptoms (lack of appetite, vomiting, nausea, headache, bone and muscle pain, etc) may develop if vitamin C is taken at ~10x the recommended level.¹ Birth defects and other pregnancy complications can arise from hypervitaminosis.¹

Dietary Sources of Vitamin C

Fruits and vegetables are the best sources of vitamin C. Vitamin C can be destroyed during cooking processes or long storage; consuming raw fruits and vegetables serves as a good source of vitamin C. Vitamin C may be fortified in grains. 

Vegetables - red and green peppers, Brussels sprouts, broccoli 

Fruits - oranges, kiwis, strawberries 

Source(s):

1. Denise M Medeiros and Robert E.C. Wildman, Advanced Human Nutrition, 4th ed. (Burlington, MA: Jones & Bartlett, 2019).

2. https://ods.od.nih.gov/factsheets/VitaminC-HealthProfessional/