Impact of folic acid fortification of the US food supply on the occurrence of neural tube defects.

CONTEXT Daily consumption of 400 microg of folic acid before conception and during early pregnancy dramatically reduces the occurrence of neural tube defects (NTDs). Before food fortification, however, only an estimated 29% of US reproductive-aged women were taking a supplement containing 400 microg of folic acid daily. The US Food and Drug Administration authorized addition of folic acid to enriched grain products in March 1996, with compliance mandatory by January 1998. OBJECTIVE To evaluate the impact of food fortification with folic acid on NTD birth prevalence. DESIGN, SETTING, AND POPULATION National study of birth certificate data for live births to women in 45 US states and Washington, DC, between January 1990 and December 1999. MAIN OUTCOME MEASURE Birth certificate reports of spina bifida and anencephaly before fortification (October 1995 through December 1996) compared with after mandatory fortification (October 1998 through December 1999). RESULTS The birth prevalence of NTDs reported on birth certificates decreased from 37.8 per 100 000 live births before fortification to 30.5 per 100 000 live births conceived after mandatory folic acid fortification, representing a 19% decline (prevalence ratio [PR], 0.81; 95% confidence interval [CI], 0.75-0.87). During the same period, NTD birth prevalence declined from 53.4 per 100 000 to 46.5 per 100 000 (PR, 0.87; 95% CI, 0.64-1.18) for women who received only third-trimester or no prenatal care. CONCLUSIONS A 19% reduction in NTD birth prevalence occurred following folic acid fortification of the US food supply. However, factors other than fortification may have contributed to this decline.