There is substantial evidence that when pregnant women consume sufficient B vitamin folate (folic acid) they are protecting their unborn babies from low birth weight and certain birth defects, and are preventing damage to the their own health. But folate requirements for nursing mothers are not well established. This study assessed the effects of dietary and supplemental folate intakes during extended lactation.
It was found that dietary folate needs were far greater than previously estimated. Lactation depletes the mother's folate stores sufficiently that supplementation with 400 mg daily may be insufficient. The 600 mg per day needed during pregnancy may be higher than is called for during lactation. Around 500 mg of supplemental folate may be adequate.
Conclusions: Nursing mothers may be getting enough folate to meet the nutritional needs their infants. But supplemental folate intake is necessary to protect the mothers themselves from using up their folate stores, putting them at risk for heart trouble and other ailments and endangering the well-being of the fetus in their next pregnancy.
Mackey AD, Picciano MF. Maternal folate status during extended lactation and the effect of supplemental folic acid. American Journal of Clinical Nutrition, Feb. 1999; vol. 69, pp285-92.