Vitamin C

Vitamin C
Yikrazuul · Public domain · source
IUPAC name	(5R)-[(1S)-1,2-Dihydroxyethyl]-3,4-dihydroxyfuran-2(5H)-one
CAS number	50-81-7
PubChem	54670067
DrugBank	DB00126
UNII	PQ6CK8PD0R
Synonyms	L-ascorbic acid, ascorbate

Vitamin C. It is an essential nutrient for numerous mammals, though notably not for most bats or guinea pigs. The Linus Pauling Institute highlights its role as a potent antioxidant and a cofactor for several vital enzymes. Deficiency leads to scurvy, a historically significant disease among sailors on long voyages.

Chemical properties

Chemically, it is a water-soluble vitamin with the molecular formula C₆H₈O₆, existing primarily as the enantiomer L-ascorbic acid or its oxidized form, dehydroascorbic acid. Its structure features an enediol group, which readily donates electrons, making it a strong reducing agent. This property is the basis for its redox activity in biological systems and its instability when exposed to heat, alkali, or transition metals like copper and iron. The Food and Drug Administration recognizes its use as a food additive (E300) for its antioxidant properties in preserving products like fruit juice.

Biological functions

It serves as an essential cofactor for enzymes involved in the biosynthesis of collagen, carnitine, and certain neurotransmitters. The hydroxylation of proline and lysine residues in collagen, catalyzed by enzymes like prolyl hydroxylase, is a critical function, providing structural integrity to connective tissue, blood vessels, and bone. It also acts as a potent antioxidant, scavenging reactive oxygen species and regenerating other antioxidants like vitamin E. Furthermore, it enhances the absorption of non-heme iron in the gastrointestinal tract and is involved in immune system functions, such as supporting the activity of leukocytes like neutrophils and lymphocytes.

Dietary sources

Excellent sources include many fruits and vegetables, particularly citrus fruits like oranges and lemons, as well as kiwifruit, strawberries, and bell peppers. Other rich sources are broccoli, Brussels sprouts, and tomatoes. The National Institutes of Health provides dietary reference intakes, noting that cooking can reduce content due to its heat-labile nature. Some fortified foods, such as certain breakfast cereals and fruit juice beverages, also contribute to intake. Historically, British naval expeditions utilized limes to prevent deficiency.

Deficiency

Prolonged inadequate intake results in scurvy, characterized by fatigue, gingivitis, petechiae, and impaired wound healing. This condition was historically prevalent among sailors during the Age of Discovery, as documented by James Lind in his 1747 clinical trial aboard HMS Salisbury. The British East India Company later mandated citrus juice on ships. Modern cases are rare but can occur in individuals with restrictive diets, alcoholism, or severe malabsorption syndromes. Biochemical signs include low levels in leukocytes and plasma before clinical symptoms appear.

Medical uses

It is used to prevent and treat scurvy, with standard doses recommended by organizations like the World Health Organization. Beyond deficiency, its role in collagen synthesis supports its use in some surgical and burn recovery settings. Research, including studies by the National Cancer Institute, has investigated its potential effects on the common cold, cardiovascular disease, and cancer, though evidence for high-dose benefits remains inconclusive. Intravenous administration was famously promoted by Linus Pauling for cancer therapy, a practice not widely adopted by mainstream oncology groups like the American Society of Clinical Oncology.

Safety

At typical dietary levels, it is very safe, with excess primarily excreted in urine. High doses, often above the Tolerable upper intake level set by the Food and Nutrition Board, can cause gastrointestinal disturbances like diarrhea and nausea. There is a theoretical risk of iron overload in individuals with hemochromatosis due to enhanced absorption. The Mayo Clinic notes that very high intakes may also increase the risk of kidney stone formation in predisposed individuals, particularly those with a history of calcium oxalate stones. Drug interactions are possible with certain chemotherapy agents and warfarin.

Category:Vitamins Category:Antioxidants Category:Essential nutrients