Increasing serum 25-hydroxyvitamin D is associated with reduced odds of long menstrual cycles in a cross-sectional study of African American women

Objective: To examine the association between serum 25-hydroxyvitamin D [ 25(OH) D] and menstrual cycle length and regularity. Design: Community-based, cross-sectional study of serum 25(OH) D (adjusted for seasonal differences in timing of blood draw) and menstrual cycle length. Women aged 23-34 years reported their gynecologic history. Menstrual cycles were described with four independent categories (normal, short, long, irregular). We used polytomous logistic regression to estimate the association between a doubling of seasonally adjusted 25(OH) D and the odds of each cycle category. Setting: Not applicable. Patient(s): A total of 1,102 African American women. Intervention(s): Not applicable. Main Outcome Measure(s): Self-reported menstrual cycle length over the previous 12 months, excluding women who were using cycle-regulating medications over the entire year. Women who reported that their cycles were too irregular to estimate'' were classified as having irregular cycles. A typical cycle length of <27 days was considered short,'' >34 days was long,'' and 27-34 days was normal.'' Result(s): The median 25(OH) D level was 14.7 ng/mL (interquartile range, 10.9-19.6 ng/mL). A doubling of 25(OH) D was associated with half the odds of having long menstrual cycles: adjusted odds ratio (aOR) 0.54, 95% confidence interval (CI) 0.32-0.89. 25-Hydroxyvitamin D was not associated with the occurrence of short (aOR 1.03, 95% CI 0.82-1.29) or irregular (aOR 1.46, 95% CI 0.88-2.41) menstrual cycles. Results were robust to several sensitivity analyses. Conclusion(s): These findings suggest that vitamin D status may influence the menstrual cycle and play a role in ovarian function. Further investigation of 25(OH) D and ovarian hormones, and prospective studies of 25(OH) D and cycle length, are needed. (C) 2016 by American Society for Reproductive Medicine.