Dosage requirements for periconceptional folic acid supplementation: accounting for BMI and lean body weight

To determine folic acid dosage requirements for individuals across a broad range of BMI values, using dose per kilogram lean body weight (LBW) as a primary predictor of systemic exposure. Steady-state folate concentrations of ≥ 15.9 nmol/L were assumed to be sufficient for reducing the risk for neural tube defects in the general population.

Data from a recent study of single-dose folic acid pharmacokinetics among 12 obese and 12 non-obese women of childbearing age were analyzed to determine expected steady-state concentrations. The mean folic acid dose per kilogram LBW that achieved serum folate concentrations of ≥ 15.9 nmol/L was applied to a broad range of BMI values to evaluate daily dose requirements.

Modest differences in folic acid requirements were noted for individuals among the non-obese, overweight, and obese categories. The current supplementation guidelines suggesting a daily dose of 0.4 mg appear to satisfy the needs of women at even the upper extremes of obesity. However, because even with appropriate folate supplementation obese women have an increased risk of neural tube defects, and they may benefit from higher intake and higher serum concentrations of folic acid.

Current guidelines recommend an adequate folic acid dose for obese women of childbearing age. Thus, it is unlikely that folate deficiency is associated with the elevated risk for neural tube defects in this population.