Serum folate and Vitamin B12 levels in women using modern oral contraceptives (OC) containing 20 microg ethinyl estradiol.

OBJECTIVE: The effects of modern oral contraceptives (OC) on serum concentrations of folate and cobalamin are controversial. STUDY DESIGN: Case-control study on the cobalamin and folate status of 71 healthy female nulligravidae using "low dose" OC for >or=3 months and 170 controls. Factors interfering with vitamin metabolism were thoroughly controlled. Serum concentrations were measured by commercial assays. The results were evaluated using Mann-Whitney's U-test and chi(2) analysis. RESULTS: OC-users showed significantly lower concentrations of cobalamin than controls. The rates of women with reduced, normal, and elevated levels differed significantly. Nine users but no control had frank cobalamin deficiency without clinical symptoms. Folate levels did not differ between the groups. Vegetarian diet, smoking or obesity did not have a significant influence. CONCLUSIONS: Routine measurement of cobalamin or folate in women using "low dose" OC is not warranted. Vitamin supplementation or different contraceptive methods should be considered in women with pre-existing cobalamin deficiency or restrictive dietary habits.