Folic acid, the most common form of folate in supplements and fortified foods, requires the enzyme methylenetetrahydrofolate reductase (MTHFR) to be converted to L-methylfolate, the activated form of folate used by the body for many biochemical reactions. About half of the population have genetic variations that reduce the ability of the MTHFR enzyme to make this conversion. For this population, L-methylfolate supplementation is far more effective in providing this form of folate.