Folate is important for cells and tissues that rapidly divide. Cancer cells divide rapidly, and drugs that interfere with folate metabolism are used to treat cancer. Methotrexate is a drug often used to treat cancer because it inhibits the production of the active form, tetrahydrofolate. Unfortunately, methotrexate can be toxic, producing side effects such as inflammation in the digestive tract that make it difficult to eat normally. Folinic acid is a form of folate that can help 'rescue' or reverse the toxic effects of methotrexate. Folinic acid is not the same as folic acid. Folic acid supplements have little established role in cancer chemotherapy. There have been cases of severe adverse effects of accidental substitution of folic acid for folinic acid in patients receiving methotrexate cancer chemotherapy. It is important for anyone receiving methotrexate to follow medical advice on the use of folic or folinic acid supplements. Low concentrations of folate, vitamin B12, or vitamin B6 may increase your level of homocysteine, an amino acid normally found in your blood. There is evidence that an elevated homocysteine level is an independent risk factor for heart disease and stroke. The evidence suggests that high levels of homocysteine may damage coronary arteries or make it easier for blood clotting cells called platelets to clump together and form a clot. However, there is currently no evidence available to suggest that lowering homocysteine with vitamins will reduce your risk of heart disease. Clinical intervention trials are needed to determine whether supplementation with folic acid, vitamin B12 or vitamin B6 can lower your risk of developing coronary heart disease. Methylene tetrahydrofolate (CH2FH4) is formed from tetrahydrofolate by the addition of methylene groups from one of three carbon donors: formaldehyde, serine, or glycine. Methyl tetrahydrofolate(CH3FH4) can be made from methylene tetrahydrofolate by reduction of the methylene group, and formyl tetrahydrofolate (CHOFH4, folinic acid) is made by oxidation of methylene tetrahydrofolate. In the form of a series of tetrahydrofolate compounds, folate derivatives are substrates in a number of single-carbon-transfer reactions, and also are involved in the synthesis of dTMP (2'-deoxythymidine-5'-phosphate) from dUMP (2'-deoxyuridine-5'-phosphate). It helps convert vitamin B12 to one of its coenzyme forms and helps synthesize the DNA required for all rapidly growing cells.