Taking folate in pregnancy and risk of maternal breast cancer.

Taking folate before conception and then for the first three months of pregnancy reduces the risk of recurrence of neural tube defects, and fortification of food has been proposed. The effects of long term exposure to high concentrations of supplemental folate are unknown, and antimetabolite effects are theoretically possible. Data on the long term effects of increased folate intake in pregnancy are limited. We followed up a large trial of folate supplementation in pregnancy from the 1960s. 4 We examined the association between folate status and death, and we also analysed the effects of folate supplementation.