Association Between Use of Oral Contraceptives and Folate Status: A Systematic Review and Meta-Analysis.

Objective: To conduct a systematic review and meta-analysis of the effect of oral contraceptive use on plasma and red blood cell (RBC) folate concentrations.
Methods: We searched Medline, EMBASE, Web of Science, and the Cochrane library for human studies published from inception to June 2013 evaluating oral contraceptive use and folate status. Case-control studies, cohort studies, and clinical trials were included. A random-effects model of outcomes was used for the meta-analysis.
Results: A total of 2831 women in 17 studies were included in the analysis. In those whose plasma folate concentrations were available, there was a significant folate-lowering effect of oral contraceptives observed (mean reduction 1.27 µg/L; 95% CI 1.85 to 0.69, P < 0.001). Similarly, after analyzing data from 1389 women in 12 studies whose RBC folate concentrations were available, significantly lower folate status was observed among oral contraceptive users (mean reduction 59.32 µg/L; 95% CI 58.03 to 23.04, P < 0.001).
Conclusion: Because of the reduction in blood folate concentrations associated with the use of oral contraceptives, it is critical for women of childbearing age to continue folate supplementation during oral contraceptive use.