
Acting with vitamin B12, 5-MTHF functions as a methyl-group donor. Many individuals don't get sufficient 5-MTHF (L-5-Methyltetrahydrofolate) which is the active form of folic acid. A deficiency of folic acid has been linked to low-birth-weight infants and neural tube defects, which is why the Centers for Disease Control recommends folic acid supplementation for all women of childbearing age.