The term folate describes a group of derivatives of pteryl glutamic acid. Folic acid is the synthetic form of folate. It is used in supplements and for food fortification.
Folate functions together with vitamin B12 to form healthy red blood cells. It is also required for normal cell division, the normal structure of the nervous system and specifically in the development of the neural tube (which develops into the spinal cord and skull) in the embryo.
There is conclusive evidence that supplements of 400μg/day of folic acid taken before conception and during the first 12 weeks of pregnancy prevent the majority of neural tube defects (e.g. spina bifida) in babies. It is recommended that all women of childbearing age who are planning a pregnancy take a daily supplement as it is difficult to achieve 400μg/day from diet alone.
Together with vitamins B6 and B12, folate is involved with the maintenance of normal blood homocysteine levels. The amino acid homocysteine is an intermediate in folate metabolism and evidence suggests that raised blood homocysteine (hyperhomocysteinemia) is an independent risk factor for cardiovascular disease. High intakes of folate have been found to lower the blood concentration of homocysteine in people genetically at risk of hyperhomocysteinemia and, as a result it has been proposed that folic acid supplementation might reduce the risk of cardiovascular disease. However, a recent meta-analysis of a number of large trials failed to demonstrate an effect of folic acid on either coronary heart disease or stroke risk.
Deficiency results in megaloblastic anaemia and may be due to poor diet or increased requirement, for example in pregnancy, from prolonged drug use or malabsorption. Megaloblastic anaemia is characterized by the release of immature red blood cell precursors into the circulation due to impairment of the normal process of maturation in the bone marrow. There may also be a low white cell and platelet count in the blood. Deficiency is often accompanied by insomnia, depression, forgetfulness and irritability.
Few adverse effects have been reported although high intakes may mask vitamin B12 deficiency and excessive intakes can cause complications if taken with certain drugs, for example anticonvulsants used in the treatment of epilepsy.
Green leafy vegetables, brown rice, peas, oranges, bananas and fortified breakfast cereals are sources of folate.
In various parts of the world folic acid is added by law to flour and bread e.g. USA, Canada and Chile. The UK is yet to commit to this fortification, largely because of concerns that high intakes of folic acid mask vitamin B12 deficiency in older people who are particularly susceptible, and some concerns regarding the relationship between folic acid and cancer. In 2005 the Scientific Advisory Committee on Nutrition (SACN) reviewed the research to underpin potential folic acid fortification in the UK and recommended that ‘mandatory fortification’ with folic acid should be implemented. Their conclusions were considered by the Food Standards Agency’s Board and it was agreed by the Board that mandatory fortification should go ahead. But before the recommendations were finalized, it was agreed to wait for the findings of ongoing trials investigating the relationship between folic acid and cancer. These trials have now finished and have been considered by SACN: an outcome is awaited.