Did national folic acid fortification reduce socioeconomic and racial disparities in folate status in the US?

BACKGROUND The purpose of this study is to determine the impact of the 1998 US Food and Drug Administration folic acid fortification policy on disparities in folate status in the United States. METHODS We use repeated cross-sectional data from the U.S. National Health and Nutrition Examination Surveys (NHANES), a nationally representative sample of over 14 000 participants ages 25 and older. We calculate pre-fortification (1991-94) and post-fortification (1999-2002) absolute differences and relative prevalence ratios of low red blood cell (RBC) folate status (<362.6 nmol), by race/ethnicity and income quartile. We also estimate kernel density plots and relative and absolute concentration curves pre- and post-fortification. RESULTS The excess prevalence of low RBC folate status associated with the lowest income quartile and black race declined by 67% and 48%, respectively, following fortification. Despite these absolute gains, the relative ratio of low folate status increased after fortification for the lowest compared with the highest income groups (from 1.27 to 2.08) and among whites compared with blacks (from 1.64 to 3.75). CONCLUSIONS The effects of the fortification policy highlight the importance of distinguishing absolute from relative differences when evaluating interventions to reduce health disparities. Targeting of high risk populations is likely needed to eliminate remaining folate disparities.