VITAMIN C

Vitamin C is also known as ascorbic acid, L-ascorbic acid, dehydroascorbic acid and the antiscorbutic vitamin. Chemically, it is called L-xyloascorbic acid and L-threo-hex-2-uronic acidy-lactone. The very highest concentrations of vitamin C are found in the adrenal and pituitary glands. High levels are also found in liver, leukocytes, brain, kidney and pancreas. Most of the vitamin C is found in liver and skeletal muscle because of their size relative to the rest of the body.

The best characterized function of vitamin C is in the synthesis of collagen connective tissue protein at the level of hydroxylation of prolyl and lysyl residues of procollagen. Vitamin C also plays important roles in the synthesis of neurotransmitters, steroid hormones, carnitine, conversion of cholesterol to bile acids, tyrosine degradation and metal ion metabolism. This vitamin also may enhance iron bioavailability. The role of ascorbic acid as a biological reducing agent may be linked to its prevention of degenerative diseases, such as cataracts, certain cancers and cardiovascular diseases.

Deficiencies: Severe ascorbic acid deficiency results in clinical scurvy which is characterized by swollen, bleeding gums, loosening of the teeth, capillary hemorrhaging, including bleeding into joints, tender and painful extremities, poor wound healing, weakness and fatigue, and psychological disturbances.

Clinical uses: The only established use of vitamin C is in the prevention and treatment of scurvy. Studies investigating possible effects on wound healing, blood pressure, colds and immune function have been epidemiological in nature or have often employed other antioxidants in addition to ascorbic acid. In most cases, the results have been unremarkable, conflicting or inconsistent, but research and interest continue in these areas.

Diet recommendations: The Recommended Dietary Allowance (RDA) for adults is 60 mg/day in the US, but may range from 30-75 mg/day in other Western countries. Intakes of 75-95 mg/day are recommended for pregnant and lactating women. The RDA is 35 mg/day in infants and 40 mg/day in children, ages 1-3 yr. About 10 mg/day is required to prevent scurvy. Increased intake of vitamin C is recommended for stress situations such as trauma, infection, strenuous exercise, or elevated environmental temperatures. The requirement in smokers may be 100 mg/day. Recent kinetic analyses suggest that intakes of 150-200 mg/day, but below 400 mg/day, obtained from the diet, may offer the most benefit in normal, healthy individuals.

Food sources: The best food sources of vitamin C are citrus fruits, berries, melons, tomatoes, potatoes, green peppers and leafy green vegetables. Vitamin C is sensitive to air, heat and water, so it can easily be destroyed by prolonged storage, overcooking and processing of foods.

Toxicity: Megadoses of vitamin C of 1000-2000 mg have commonly been associated with gastrointestinal disturbances (nausea, abdominal cramps and diarrhea). In general, megadoses of vitamin C should be avoided in individuals with a history of renal stones due to oxalate formation or hemochromatosis or other diseases related to excessive iron accumulation. Excess vitamin C may predispose premature infants to hemolytic anemia due to the fragility of their red blood cells. In healthy individuals, it appears that megadoses of up to 1000 mg/day of vitamin C are well tolerated and not associated with any consistent adverse effects. Concern of its pro-oxidant properties is stimulating renewed interest in its potential long-term toxicity.

Recent research: Work continues to develop and define a useful functional test for vitamin C status, such as activities of certain enzymes, white cell viability, or perhaps a test related to the immune response. Investigations continue into developing a better understanding of the role of vitamin C beyond preventing vitamin C deficiency. Some examples are establishing optimal or pharmacologic uses of the vitamin and discerning its role as an antioxidant/pro-oxidant in human biology. Clinical studies also continue to define the role of vitamin C in the prevention and treatment of cataracts, certain cancers and other human diseases.

For Further Information:

Harris, J. R. (1996) Ascorbic Acid: Biochemistry and Biomedical Cell Biology. Subcellular Biochemistry, vol. 25, Plenum Press, NY.

Weber, P., Bendich, A. & Schalch, W. (1995) Vitamin C and human health. A review of recent data relevant to human requirements. Internat. J. Vit. Nutr. Res. 66: 19-30.

Rumsey, S. C. & Levine, M. (1998) Absorption, transport and disposition of ascorbic acid in humans. J. Nutr. Biochem. 9: 116-130.

Prepared By:

Michael Dubick, Ph.D.
Chief, Trauma Studies Branch
U.S. Army Institute of Surgical Research
3400 Rawley E. Chambers Avenue
Fort Sam Houston, TX 78234-6315
Phone: 210-916-3680
FAX: 210-916-2942
Email: michael.dubick@cs.amedd.army.mil

Stanley T. Omaye, Ph.D.
Professor, Department of Nutrition
University of Nevada
Fleischmann Building
Room 113
Reno, NV 89557
Phone: 702-784-6447
FAX: 702-784-6449
Email: omaye@unv.edu