Lower RBC folate concentration is a population weighted estimate from the blood specimens collected from women aged 15 to 44 years as part of the standard NHANES protocol. According to data from the National Health and Nutrition Examination Survey (NHANES), median RBC folate concentrations increased substantially between 1988-94 and 1999-2000, pre- and post-fortification with folic acid, and then declined slightly in the post-fortification period (Pfeiffer et al., 2007, CDC, 2007). In 1999-2000, HP2010 objective 16-16b was met for all nonpregnant US women aged 15-44 y, and for non-Hispanic white and Mexican-American, but not non-Hispanic black women (CDC, 2007). The decreases from 1999-2000 to 2003-2004 were not in the low end of the distribution and thus did not raise concerns about inadequate status. However, continued monitoring remains important. The concentration of RBC folate associated with the lowest neural tube defect risk is unknown (Daly et al., 1995; Wald et al., 1998). In 2007-2010, the 25th percentile of RBC folate among US women aged 15-44 years was 337 ng/ml. Given that folic acid has been shown to reduce NTDs, reductions in the proportion of women with lower RBC folate concentrations should move us towards this goal.
The baseline was revised from 24.5% (2003-06 ) to 24.9% (2007-10) because there was a change in the methodology. The target was proportionally adjusted from 22.1% to 22.4%.