Folate status in the US population 20 y after the introduction of folic acid fortification

Abstract

Background: Enriched cereal-grain products have been fortified in the United States for >20 y to improve folate status in women of reproductive age and reduce the risk of folic acid-responsive neural tube birth defects (NTDs).

Objectives: Our objectives were to assess postfortification changes in folate status in the overall US population and in women aged 12-49 y and to characterize recent folate status by demographic group and use of folic acid-containing supplements.

Methods: We examined cross-sectional serum and RBC folate data from the NHANES 1999-2016.

Results: Serum folate geometric means increased from 2007-2010 to 2011-2016 in persons aged ≥1 y (38.7 compared with 40.6 nmol/L) and in women (35.3 compared with 37.0 nmol/L), whereas RBC folate showed no significant change. Younger age groups, men, and Hispanic persons showed increased serum and RBC folate concentrations, whereas non-Hispanic black persons and supplement nonusers showed increased serum folate concentrations. The folate insufficiency prevalence (RBC folate <748 nmol/L; NTD risk) in women decreased from 2007-2010 (23.2%) to 2011-2016 (18.6%) overall and in some subgroups (e.g., women aged 20-39 y, Hispanic and non-Hispanic black women, and supplement nonusers). After covariate adjustment, RBC folate was significantly lower in all age groups (by ∼10-20%) compared with persons aged ≥60 y and in Hispanic (by 8.2%), non-Hispanic Asian (by 12.1%), and non-Hispanic black (by 20.5%) compared with non-Hispanic white women (2011-2016). The 90th percentile for serum (∼70 nmol/L) and RBC (∼1800 nmol/L) folate in supplement nonusers aged ≥60 y was similar to the geometric mean in users (2011-2014).

Conclusions: Blood folate concentrations in the US population overall and in women have not decreased recently, and folate insufficiency rates are ∼20%. Continued monitoring of all age groups is advisable given the high folate status particularly in older supplement users.

Keywords: RBC folate; folate deficiency; folate insufficiency; race-ethnicity; serum folate; supplement use; women of reproductive age.

Published by Oxford University Press on behalf of the American Society for Nutrition 2019.

Figures

FIGURE 1

Pre- and postfortification median and 90th percentile concentrations of serum (A) and RBC (B) folate in persons aged ≥3 y by survey period, NHANES 1988–2016. Folic acid fortification became mandatory in 1998. Lines between 1988–1994 and 1999–2000 are dashed to indicate that there were several years between these 2 surveys. Error bars represent 95% CIs. For NHANES 1988–1994, biological samples were collected from persons aged ≥4 y only. The 1988–1994 and 1999–2006 radioassay data were adjusted (13) to make them comparable to the 2007–2016 RBC microbiologic assay, 2007–2010 serum microbiologic assay, and 2011–2016 serum LC-MS/MS data. For sample sizes (n), see Supplemental Table 2 for 1999–2016; sample sizes for 1988–1994 were 22,939 (serum folate) and 22,438 (RBC folate).