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Folic acid source, usual intake, and folate and vitamin B-12 status in US adults: National Health and Nutrition Examination Survey (NHANES) 2003–2006^1,2,3,4

¹ From the Office of Public Health Genomics, Centers for Disease Control and Prevention, Atlanta, GA (QY); the Division of Birth Defects and Developmental Disabilities, National Center on Birth Defects and Developmental Disabilities, Centers for Disease Control and Prevention, Atlanta, GA (MEC, HCH, and RJB); the Department of Statistics, Iowa State University, Ames, IA (AC); the Food Science and Human Nutrition Department, University of Florida, Gainesville, FL (LBB); the Division of Laboratory Sciences, National Center for Environmental Health, Centers for Disease Control and Prevention, Atlanta, GA (CMP).

² QY and MEC contributed equally to this work.

³ The findings and conclusions in this report are those of the authors and do not necessarily represent the official position of the Centers for Disease Control and Prevention.

⁴ Address correspondence to Q Yang, Office of Public Health Genomics, Centers for Disease Control and Prevention, 1600 Clifton Road, NE, MS E-61, Atlanta, GA 30333. E-mail: qay0{at}cdc.gov.

ABSTRACT

Background: US adults have access to multiple sources of folic acid. The contribution of these sources to usual intakes above the tolerable upper level (UL) (1000 µg/d) and to folate and vitamin B-12 status is unknown.

Objective: The objective was to estimate usual folic acid intake above the UL and adjusted serum and red blood cell folate, vitamin B-12, methylmalonic acid, and homocysteine concentrations among US adults by 3 major folic acid intake sources—enriched cereal-grain products (ECGP), ready-to-eat cereals (RTE), and supplements (SUP)—categorized into 4 mutually exclusive consumption groups.

Design: We used data from the National Health and Nutrition Examination Survey (NHANES) 2003–2006 (n = 8258).

Results: Overall, 2.7% (95% CI: 1.9%, 3.5%) of adults consumed more than the UL of folic acid. The proportions of those who consumed folic acid from ECGP only, ECGP+RTE, ECGP+SUP, and ECGP+RTE+SUP were 42%, 18%, 25%, and 15%, respectively. Of 60% of adults who did not consume supplements containing folic acid (ECGP only and ECGP+RTE), 0% had intakes that exceeded the UL. Of 34% and 6% of adults who consumed supplements with an average of 400 and >400 µg folic acid/d, <1% and 47.8% (95% CI: 39.6%, 56.0%), respectively, had intakes that exceeded the UL. Consumption of RTE and/or supplements with folic acid was associated with higher folate and vitamin B-12 and lower homocysteine concentrations, and consumption of supplements with vitamin B-12 was associated with lower methylmalonic acid concentrations (P < 0.001).

Conclusion: At current fortification levels, US adults who do not consume supplements or who consume an average of 400 µg folic acid/d from supplements are unlikely to exceed the UL in intake for folic acid.

Received for publication July 17, 2009. Accepted for publication September 12, 2009.