Objective: Since January 1998, the Federal Drug Administration has required folic acid fortification of all enriched cereal-grain products in the U.S. This program intended to increase folic acid intake among women of childbearing age in order to decrease their risk of pregnancies affected by neural tube defects. The aim of this study was to explore the changes in serum and erythrocyte folate status of the adult U.S. population following folic acid fortification of enriched cereal-grain products and to explore accompanying changes in food sources and dietary total folate intake.

Methods: We compared data from two National Health and Nutrition Examination Surveys (NHANES): NHANES III, conducted during 1988 to 1994, reflecting the time prior to folate fortification, and NHANES 1999-2000, reflecting the time period after fortification.

Results: Mandatory folic acid fortification led to significant increases in both serum and erythrocyte folate concentrations in all sex and age groups. In the overall study population the mean serum folate concentration increased more than two-fold (136%), from 11.4 nmol/L to 26.9 nmol/L, and the mean erythrocyte folate concentration increased by 57 percent, from 375 nmol/L to 590 nmol/L. Less than 10% of women of childbearing age reached the recommended erythrocyte folate concentration of greater than 906 nmol/L that has been shown to be associated with a significant reduction in neural tube defect (NTD) risk. After fortification, the category "bread, rolls, and crackers" became the single largest contributor of total folate to the American diet, contributing 15.6% of total intake, surpassing vegetables, which were the number one folate food source prior to fortification. Dietary intake of total folate increased significantly in almost all sex and age groups, except in females over 60 years of age. The mean dietary total folate intake of the study population increased by 76 microg/d (28%), from 275 microg/d to 351 microg/d.

Conclusions: The fortification of enriched cereal-grain products with folic acid led to a significant improvement of blood folate status of the overall adult, non-supplement using, US population. However, women of childbearing age may take folic acid supplements to reach erythrocyte folate levels that have been associated with decreased risk of NTDs.