Periconceptional folate and neural tube defect

The US Public Health Service recommends that all women in the United States who might possibly become pregnant should consume 0.4 mg folic acid/d to lower the incidence of neural tube defect (NTD). This paper reviews the bases for this recommendation: controlled trials of periconceptional folate, observational studies of folate supplementation, studies relating dietary folate to NTD, a trial of dietary education aimed at lowering the rate of NTD, and studies of the relationship to NTD of serum and red blood cell folate concentrations. It remains unclear that trials to prevent recurrent NTD apply directly to occurrent NTD, and the minimum necessary dose of folate is unknown. Given the potential dangers of high levels of folate in the general diet, particularly the masking of the hematologic effects of vitamin B-12 deficiency in elderly persons, with the consequent possibility of vitamin B-12 deficiency presenting as severe, irreversible neurologic disease, it is suggested that, until the impact of increasing the general folate level of the diet is better understood, tablet supplementation of folate to women of child-bearing age is preferable as an interim measure to increased food fortification.