Biological Function of Folic Acid
One-carbon metabolism
The only function of folate coenzymes in the body appears to be mediating the transfer of one-carbon units (2). Folate coenzymes act as acceptors and donors of one-carbon units in a variety of reactions critical to the metabolism of nucleic acids and amino acids (3).

Nucleic acid metabolism
Folate coenzymes play a vital role in DNA metabolism through two different pathways.1) The synthesis of DNA from its precursors is dependent on folate coenzymes. 2) A folate coenzyme is required for the synthesis of methionine, and methionine is required for the synthesis of S-adenosylmethionine (SAM). SAM is a methyl group (one-carbon unit) donor used in many biological methylation reactions, including the methylation of a number of sites within DNA and RNA. Methylation of DNA may be important in cancer prevention.

Amino acid metabolism
Folate coenzymes are required for the metabolism of several important amino acids. The synthesis of methionine from homocysteine requires a folate coenzyme as well as a vitamin B12 dependent enzyme. Thus, folate deficiency can result in decreased synthesis of methionine and a build up of homocysteine. Increased levels of homocysteine may be a risk factor for heart disease, as well as several other chronic diseases.

Signs and Symptoms of Deficiency
Folate deficiency occurs in a number of situations. For example, low dietary intake and diminished absorption, as in alcoholism, can result in a decreased supply of folate. Certain conditions like pregnancy or cancer result in increased rates of cell division and metabolism, leading to an increase in the body’s demand for folate (5). Several medications may also contribute to deficiency.

References:

1. Food and Nutrition Board, Institute of Medicine. Folic Acid. Dietary Reference Intakes: Thiamin, Riboflavin, Niacin, Vitamin B-6, Vitamin B-12, Pantothenic Acid, Biotin, and Choline. Washington, D.C.: NationalAcademy Press; 1998:193-305. (National Academy Press).
2. Choi SW, Mason JB. Folate and carcinogenesis: an integrated scheme. J Nutr. 2000;130(2):129-132. (PubMed).
3. Bailey LB, Gregory JF, 3rd. Folate metabolism and requirements. J Nutr. 1999;129(4):779-782. (PubMed).
4. Gerhard GT, Duell PB. Homocysteine and atherosclerosis. CurrOpinLipidol. 1999;10(5):417-428. (PubMed).
5. Herbert V. Folic acid. In: Shils M, Olson JA, Shike M, Ross AC, eds. Nutrition in Health and Disease. 9th ed. Baltimore: