Fig. 2.

 Folic acid and folates are precursors to 5-methyltetrahydrofolate, which in turn acts as a methyl group donor for the re-methylation of homocysteine to methionine. Folate deficiency thus leads indirectly to elevated plasma homocysteine concentrations. Folate deficiency also results in lower concentrations of S-adenosyl methionine, an important methyl group donor for epigenetic processes (gene methylation) and for basic processes of cell metabolism (DNA synthesis, protein synthesis).