Author
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SELHUB, JACOB - TUFTS-HNRCA |
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Submitted to: Journal of Nutrition Health and Aging
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 8/1/2001 Publication Date: 2/1/2002 Citation: SELHUB, J. FOLATE, VITAMIN B12 AND VITAMIN B6 AND ONE CARBON METABOLISM. JOURNAL OF NUTRITION HEALTH AND AGING. 2002;6:39-42. Interpretive Summary: The vitamin folic acid is involved in many vital processes in the body, including the synthesis of DNA, RNA proteins and other important functions called methylations. Other participants in these functions include vitamin B6 and vitamin B12. Because of these functions, low levels of these vitamins or inadequate intake could have adverse health effect throughout life. This article reviews the recent evidence on the relationship between folic acid and the other two B vitamins on the health of the elderly. Many of the ills that afflict the elderly including cancers, cardiovascular disease and brain dysfunctions are related to inadequate intake of these vitamins. It is important therefore that proper vitamin nutrition is maintained throughout life. Technical Abstract: The vitamins folic acid, B12 and B6 and B2 are the source of coenzymes which participate in one carbon metabolism. In this metabolism, a carbon unit from serine or glycine is transferred to tetrahydrofolate (THF) to form methylene-THF. This is either used as such for the synthesis of thymidine, which is incorporated into DNA, oxidized to formyl-THF which is used for the synthesis of purines, which are building blocks of RNA and DNA, or it is reduced to methyl-THF which used to methylate homocysteine to form methionine, a reaction which is catalyzed by a B12-containing methyltransferase. Much of the methionine which is formed is converted to S-adenosylmethionine (SAM), a universal donor of methyl groups, including DNA, RNA, hormones, neurotransmitters, membrane lipids, proteins and others. Interest has been growing regarding the possibility that certain diseases that afflict the aging population may be in part explained by inadequate intake or inadequate status of these vitamins. Homocysteine was shown recently to be a risk factor for cardiovascular disease, stroke and thrombosis when its concentration in plasma is slightly elevated. There are now data which show association between elevated plasma homocysteine levels and loss of neurocognitive function and Alzheimer's disease. These associations could be due to a neurotoxic effect of homocysteine or to decreased availability of SAM which results in hypomethylation in the brain tissue. Hypomethylation is also thought to exacerbate depressive tendency in people, and for (colorectal) cancer DNA hypomethylation is thought to be the link between the observed relationship between inadequate folate status and cancer. |
