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Folate status and homocysteine response to folic acid doses and withdrawal among young Chinese women in a large-scale randomized double-blind trial ^1,2,3,4

¹ From the National Reference Laboratory on Reproductive and Child Health, Ministry of Health and National Center for Maternal and Infant Health, Peking University Health Science Center, Beijing, China (LH, ZL, J-HZ, LZ, and SL); the National Center on Birth Defects and Developmental Disabilities, Centers for Disease Control and Prevention, Atlanta, GA (Q-HY, DJH, JDE, and RJB); the Food Science and Human Nutrition Department, University of Florida, Gainesville, FL (LBB); the Maternal and Child Health Institute, Xianghe County, Hebei Province, China (B-LZ); the National Center for Preparedness, Detection, and Control of Infectious Diseases, Division of Global Migration and Quarantine and the Thailand MOPH-US CDC Collaboration, Bangkok, Thailand (JG). LH and Q-HY contributed equally to the study

Background: There are no large randomized trials of the effect of folic acid dosing regimens on blood folate and homocysteine concentrations.

Objective: We aimed to evaluate the changes in folate and homocysteine concentrations in response to different folic acid doses and to withdrawal in young women not exposed to other sources of folic acid.

Design: Women (n = 1108) were randomly assigned to 1 of 6 intervention groups for which daily intakes of folic acid for 6 mo were 100 µg 1 time/d, 25 µg 4 times/d, 400 µg 1 time/d, 100 µg 4 times/d, 4000 µg 1 time/d, or 4000 µg 1 time/wk. Plasma and red blood cell folate and homocysteine concentrations were measured at baseline; at 1, 3, and 6 mo; and 3 mo after the discontinuation of folic acid.

Results: Folate and homocysteine concentrations were not different at baseline between the groups who had the same daily intake of folic acid as a single dose or multiple doses (P = 0.058). Plasma folate concentrations plateaued at 3 mo with 108% (95% CI: 97.7%, 120%), 259% (95% CI: 240%, 279%), 460% (95% CI: 417%, 503%), and 142% (95% CI: 123%, 162%) observed increases for the folic acid groups receiving 100, 400, and 4000 µg/d and 4000 µg/wk, respectively. The rate of reduction in folate concentrations during the 3 mo after cessation of folic acid was dose-dependent—higher intakes were associated with faster reductions.

Conclusions: Changes in folate and homocysteine concentrations were unaffected by different dosing schedules. After folic acid cessation, blood folate declined rapidly, which indicated that the intervention-enhanced folate status was rapidly diminished.