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

Context Daily consumption of 400 mug of folic acid before conception and du ring early pregnancy dramatically reduces the occurrence of neural tube def ects (NTDs), Before food fortification, however, only an estimated 29% of U S reproductive-aged women were taking a supplement containing 400 mug of fo lic acid daily. The US Food and Drug Administration authorized addition of folic acid to enriched grain products in March 1996, with compliance mandat ory by January 1998. Objective To evaluate the impact of food fortification with folic acid on N TD birth prevalence. Design, Setting, and Population National study of birth certificate data fo r 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 anenceph aly 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 decreas ed from 37.8 per 100000 live births before fortification to 30.5 per 100000 live births conceived after mandatory folic acid fortification, representi ng 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 100000 to 46.5 per 100000 (PR, 0.87; 95% CI, 0.64-1.18) for women wh o received only third-trimester or no prenatal care. Conclusions A 19% reduction in NTD birth prevalence occurred following foli c acid fortification of the US food supply. However, factors other than for tification may have contributed to this decline.