Fortification of enriched cereal-grain products with folic acid to help prevent pregnancies affected by a neural tube defect (NTD) (e.g., spina bifida or anencephaly) became mandatory in the United States in January 1998. Data from the 1999--2000 National Health and Nutrition Examination Survey (NHANES) indicated that median serum folate* concentrations in nonpregnant women of childbearing age had increased substantially, compared with concentrations during a period (1988--1994) before fortification was mandated (1). This report uses NHANES data to update those findings and assess trends in serum folate and red blood cell (RBC) folate levels† by race/ethnicity from the 1999--2000 survey through the 2003--2004 survey. The results of these comparisons indicated that median serum folate concentrations among nonpregnant women of childbearing age decreased 16% from 1999--2000 through 2003--2004, and RBC folate concentrations decreased 8%. All women of childbearing age who are capable of becoming pregnant should consume 400 µg of folic acid daily to reduce the occurrence of NTD-affected pregnancies (2).
In 1992, the Public Health Service recommended that all women of childbearing age who are capable of becoming pregnant consume 400 µg of folic acid daily to reduce the number of cases of NTDs (2). In 1996, a final rule published by the Food and Drug Administration (FDA) required the addition of folic acid to a range of enriched cereal-grain products (e.g., bread, rolls, macaroni products, rice, corn meal, corn grits, and farina); the manufacturers' full-compliance date was January 1998 (3). In addition to improved dietary habits and folic acid fortification, the Public Health Service also recommended the use of dietary supplements containing folic acid (2); however, survey data have not indicated a substantial change in supplement use since the fortification mandate (4).
NHANES 1999--2000, 2001--2002, and 2003--2004 are annual surveys of persons of all ages selected through a stratified, multistage probability sampling of the civilian, noninstitutionalized U.S. population. A household interview and physical examination are conducted for each survey participant; blood samples are collected by venipuncture during the physical examination. For all study years, serum folate and RBC folate concentrations were measured by CDC (1). Long-term quality-control data for these assays indicated no analytic drift; external proficiency testing challenges also indicated stable performance. Serum folate and RBC folate concentrations for nonpregnant women aged 15--44 years were distributed by percentile, and medians were calculated. Because no satisfactory nonparametric approach exists for statistical analysis of survey data that compares medians, geometric mean serum folate and RBC folate concentrations were calculated; trends in geometric means from 1999--2000 through 2003--2004 were evaluated using a t test calculated from a linear regression model. The values derived for the medians and geometric means were consistent.
During 2001--2002 and 2003--2004, median (50th percentile) serum folate concentrations among women aged 15--44 years were 11.4 ng/mL and 10.6 ng/mL, respectively. Thus, a statistically significant 16% decline was observed from 1999--2000 (12.6 ng/mL) through 2003--2004 based on comparison of geometric means (p<0.001) (Table 1). Similarly, RBC folate concentrations decreased 8%, from 255 ng/mL during 1999--2000 to 235 ng/mL during 2003--2004 (p=0.028).
When analyzed by race/ethnicity, median serum folate concentrations declined significantly from 1999--2000 through 2003--2004 among all three populations considered (non-Hispanic whites [p=0.008], non-Hispanic blacks [p=0.023], and Mexican Americans [p<0.001]). The largest decrease (16%) was noted among non-Hispanic whites (Table 2). However, the median serum folate concentration was lowest among non-Hispanic blacks during all three survey periods.
Although non-Hispanic white and Mexican-American women exceeded the 2010 national health objective (objective 16-16b) for median RBC folate concentration (220 ng/mL) during all three survey periods, non-Hispanic black women had not met this objective. Trend differences from 1999--2000 through 2003--2004 in RBC folate concentrations were not statistically significant among each of the three racial/ethnic populations (non-Hispanic whites [p=0.106], non-Hispanic blacks [p=0.076], and Mexican Americans [p=0.064]).
Reported by: SL Boulet, DrPH, Q Yang, PhD, C Mai, MPH, J Mulinare, MD, National Center on Birth Defects and Developmental Disabilities; CM Pfeiffer, PhD, National Center on Environmental Health, CDC.
Contact: Donna Vandergraff, Phone: 765-494-8228, E-mail: vandergraff@purdue.edu
Funded by Folic Acid Council grant from March of Dimes.
