“BV is a highly prevalent vaginal infection that is associated with adverse pregnancy outcomes,” write Lisa M. Bodnar, from the University of Pittsburgh Graduate School of Public Health in Pittsburgh, Pennsylvania, and colleagues. “Vitamin D exerts an influence on the immune system and may play a role in BV.”

The goal of this study was to determine the association in early pregnancy between maternal vitamin D status and the prevalence of BV, which was diagnosed with use of Gram stain vaginal smears interpreted by Nugent’s method. Before 16 weeks’ gestation, 469 women who enrolled in a pregnancy cohort study had a pelvic examination and measurement of serum 25-hydroxyvitamin D [25(OH)D] level.

Based on a Nugent score of 7 to 10, BV was diagnosed in approximately 41% of women. In more than half (52%) of women, serum 25(OH)D concentration was less than 37.5 nmol/L. Compared with women with normal vaginal flora, those with BV had lower mean unadjusted serum 25(OH)D concentration (29.5 nmol/L; 95% confidence interval [CI], 27.1 – 2.0 vs 40.1 nmol/L; 95% CI, 37.0 – 43.5; P < .001).

As vitamin D levels improved, the prevalence of BV decreased (P < .001). The prevalence of BV was approximately 57% in women with a serum 25(OH)D concentration of less than 20 nmol/L, and it was 23% in women with a serum 25(OH)D concentration of more than 80 nmol/L. A dose-response association was noted between 25(OH)D level and BV prevalence. As 25(OH)D levels increased to 80 nmol/L, the prevalence of BV decreased, and it then plateaued at higher 25(OH)D levels.

After adjustment for race and sexually transmitted diseases, there were 1.65-fold (95% CI, 1.01 – 2.69) and 1.26-fold (95% CI, 1.01 – 1.57) increases in the prevalence of BV associated with a serum 25(OH)D concentration of 20 and 50 nmol/L, respectively.

“Vitamin D deficiency is associated with BV and may contribute to the strong racial disparity in the prevalence of BV,” the study authors write.

Limitations of this study include small number of women with optimal vitamin D status, cross-sectional analysis, possible unmeasured or unknown confounders, and lack of data on parathyroid hormone concentrations or other functional indicators of vitamin D status.

“A better understanding of the vitamin D-BV relation will be ascertained with prospective studies of ‘incident’ BV infections, persistent infections, and infections that spontaneously resolve,” the study authors conclude. “It is also of considerable importance to explore the effect of maternal vitamin D on particular organisms or flora patterns other than BV that are linked to adverse outcomes. If our results are replicated in other studies, vitamin D deficiency may contribute to the racial disparity in the prevalence of BV and other adverse outcomes of pregnancy.”

The National Institutes of Health supported this study. The study authors have disclosed no relevant financial relationships.

J Nutr. 2009;139:1157-1161.