Bacterial vaginosis and season, a proxy for vitamin D status

Low serum vitamin D concentration has been associated with increased prevalence of bacterial vaginosis (BV) among pregnant women, but the few studies conducted in nonpregnant women have produced inconsistent results. Because serum vitamin D concentration is generally higher in the summer and fall than winter and spring, if vitamin D insufficiency causes BV, then BV would be expected to be more common during seasons with lower vitamin D concentrations.

The Longitudinal Study of Vaginal Flora followed up women in Birmingham, Alabama (33.5° latitude), quarterly for up to 1 year. We used a case-crossover design with conditional logistic regression among women who attended visits in each season, to assess the adjusted association between season and BV. We compared each woman's BV status in summer, fall, and spring to her own status in winter.

Among the 3620 women in the parent study, 2337 attended visits in each season; BV prevalence was 40% in winter, 38% in spring, and 41% in summer and fall. One thousand three hundred thirty-five women had BV at some but not all visits and were therefore included in the case-crossover analysis. Season was not associated with BV in women who were BV negative at study entry (odds ratio vs. winter were 1.0 for spring, 1.0 for summer, and 0.9 for fall; P = 0.81). Among women BV positive at study entry, the corresponding odds ratios were 0.9, 1.4, and 1.4 (P < 0.001).

These results do not support an association between vitamin D, measured through the proxy variable of season, and BV.