Folates function as cofactors in the transfer and utilization of one carbon groups. These reactions are essential for the production of purines and pyrimidines for DNA synthesis. Folates also play a major role in the regeneration of methionine from homocysteine. In pregnancy, poor body stores of folates may lead to neural tube defects, such as spina bifida. Chronic folate deficiency is often the cause of a megaloblastic anaemia. Certain types of cancers and Alzheimer’s disease have also been linked to reduced folate status.

The predominant form of the vitamin in plasma and red cells is 5-methyltetrahydrofolate (5MTHF). 5MTHF is formed from 5,10-methylenetetrahydrofolate in a reduction reaction, catalysed by methylenetetrahydrofolate reductase (MTHFR). Following synthesis, 5MTHF supplies methyl groups for the remethylation of homocysteine to methionine, hence deficiency of 5MTHF will result in an elevated level of homocysteine, which has been considered to be a cardiovascular risk factor. Different MTHFR polymorphisms have an impact on synthesis of 5MTHF. The base pair substitution of cytosine (C) for thymidine (T) at position 677 reduces the activity of this enzyme.