Background: Higher pre-pregnancy body mass index (BMI) is associated with increased risk of neural tube defects (NTDs) and possibly other negative birth outcomes in the offspring. The mechanism for this association remains unknown. Lower maternal folate level has been implicated in the etiology of NTDs in general. The association of BMI with folate level, however, has not been investigated.
Methods: The present study examines the association of BMI with folate level in childbearing age women before and after the 1998 U.S. folate fortification program of cereal products, using data from two cross-sectional surveys of the U.S. population, the third wave of the National Health and Nutrition Examination Survey (NHANES III; 1988-1994) and the more recent wave of this survey (NHANES 1999-2000).
Results: After controlling for intake of folate in food and nutritional supplements, increased BMI in childbearing age women was associated with a lower serum folate level in both surveys (p < 0.001). Using data from NHANES 1999-2000, it was estimated that women in the 30.0 + kg/m2 BMI category would need to take an additional 350 microg/day of folate to achieve the same serum folate level as women in the < 20.0 kg/m2 category.
Conclusion: Lower folate level may be one mechanism linking higher maternal BMI and increased risk of NTDs in the offspring. If corroborated in future studies, findings from this study suggest a need for a higher dose of folate supplement in heavier childbearing age women.