Serum vitamin D status and bacterial vaginosis prevalence and incidence in Zimbabwean women

Background: Bacterial vaginosis, a highly prevalent vaginal condition, is correlated with many adverse reproductive outcomes. In some studies, low vitamin D status (measured as serum 25-hydroxyvitamin D, 25[OH]D) has been associated with increased prevalence of bacterial vaginosis.

Objectives: We examined the cross-sectional association between vitamin D status and prevalence of bacterial vaginosis, separately for pregnant and nonpregnant women. Using prospectively collected data, we also characterized the effect of time-varying vitamin D status on incident bacterial vaginosis.

Study design: We quantified 25(OH)D in stored sera collected quarterly from 571 Zimbabwean women participating in the Hormonal Contraception and Risk of HIV Acquisition Study. The analysis was restricted to women not using hormonal contraception. We characterized associations between vitamin D insufficiency (defined as 25[OH]D ≤ 30 ng/mL vs > 30 ng/mL) and prevalence of bacterial vaginosis among nonpregnant women at the enrollment visit and among pregnant women at the first follow-up visit that pregnancy was detected. Among women who were negative for bacterial vaginosis at enrollment (n = 380), we also assessed the effect of time-varying vitamin D status on incident bacterial vaginosis. We used the Liaison 25(OH)D total assay to measure 25(OH)D. Bacterial vaginosis was diagnosed via Nugent score.

Results: At enrollment, the prevalence of bacterial vaginosis was 31% and overall median 25(OH)D was 29.80 ng/mL (interquartile range, 24.70-34.30 ng/mL): 29.75 ng/mL (interquartile range, 25.15-33.95 ng/mL) among women with bacterial vaginosis, and 29.90 ng/mL (interquartile range, 24.70-34.50 ng/mL) among women without bacterial vaginosis. Among pregnant women, the prevalence of bacterial vaginosis was 27% and overall median 25(OH)D was 29.90 ng/mL (interquartile range, 24.10-34.00 ng/mL): 30.80 ng/mL (interquartile range, 26.10-36.90 ng/mL) among women with bacterial vaginosis, and 29.10 ng/mL (interquartile range, 23.80-33.45 ng/mL) among women without bacterial vaginosis. Vitamin D levels ≤ 30 ng/mL were not associated with a prevalence of bacterial vaginosis in nonpregnant women (adjusted prevalence ratio, 1.04; 95% confidence interval, 0.81-1.34) or pregnant women (adjusted prevalence ratio, 0.88, 95% confidence interval, 0.51-1.54). Vitamin D levels ≤ 30 ng/mL were similarly not associated with incident bacterial vaginosis (adjusted hazard ratio, 0.98, 95% confidence interval, 0.73-1.31). Our findings were robust to alternative specifications of vitamin D status including using a cut point for vitamin D deficiency of < 20 ng/mL vs ≥ 20 ng/mL and modeling 25(OH)D as a continuous variable.

Conclusion: Among reproductive-age Zimbabwean women, insufficient vitamin D was not associated with increased bacterial vaginosis prevalence or incidence. Given established associations between bacterial vaginosis and poor reproductive outcomes, identification of factors leading to high bacterial vaginosis prevalence is urgently needed.