Steady state folate concentrations achieved with 5 compared with 1.1 mg folic acid supplementation among women of childbearing age

Background: Synthetic folic acid (0.4–1.0 mg) consumed during the periconceptional period has been shown to reduce the risk of neural tube defects. Women with poor supplement adherence or a previous pregnancy affected by a neural tube defect may need to take higher doses of folic acid (4–5 mg). However, there are limited data on the pharmacokinetics of higher folic acid doses. Objective: Our aim was to compare steady state folate concentrations in women of childbearing age who took 5 or 1.1 mg folic acid daily for 30 wk. Design: Forty nonpregnant women aged between 18 and 45 y, who did not take folic acid supplements, were enrolled in the study. Subjects were randomly assigned to take either 5 or 1.1 mg folic acid daily for 30 wk. Plasma and red blood cell (RBC) folate concentrations were measured at baseline and at weeks 2, 4, 6, 12, and 30. Results: There was no significant difference in baseline RBC folate concentrations between the 2 groups (1121 6 410 and 1035 6 273 nmol/L for the 5- and 1.1-mg folic acid groups, respectively). Significant differences in RBC folate were detected between groups at weeks 4, 6, 12, and 30. RBC folate concentrations by week 30 were 2339 6 782 and 1625 6 339 nmol/L for the 5- and 1.1-mg folic acid groups, respectively. Conclusion: The use of 5 mg folic acid among women of childbearing age produced higher blood folate concentrations, with a faster rate of folate accumulation, compared with 1.1 mg folic acid. Am J Clin Nutr 2009;89:844–52.