Tetrahydrofolate is a soluble coenzyme (vitamin B9) that is synthesized de novo by plants and microorganisms, and absorbed from the diet by animals. It is composed of three distinct parts: a pterin ring, a p-ABA (p-aminobenzoic acid) and a polyglutamate chain with a number of residues varying between 1 and 8. Only the tetra-reduced form of the molecule serves as a coenzyme for C1 transfer reactions. In biological systems, the C1-units exist under various oxidation states and the different tetrahydrofolate derivatives constitute a family of related molecules named indistinctly under the generic term folate. (PMID 16042593). 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. -- Wikipedia; Signs of folic acid deficiency are often subtle. Diarrhea, loss of appetite, and weight loss can occur. Additional signs are weakness, sore tongue, headaches, heart palpitations, irritability, and behavioral disorders. Women with folate deficiency who become pregnant are more likely to give birth to low birth weight and premature infants, and infants with neural tube defects. In adults, anemia is a sign of advanced folate deficiency. In infants and children, folate deficiency can slow growth rate. Some of these symptoms can also result from a variety of medical conditions other than folate deficiency. It is important to have a physician evaluate these symptoms so that appropriate medical care can be given. -- Wikipedia; 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. -- Wikipedia. Low concentrations of folate, vitamin B12, or vitamin B6 may increase the level of homocysteine, an amino acid normally found in 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. -- Wikipedia.