Your Family Physician
Thursday, June 4, 2009
Vitamin D Deficiency Linked to Bacterial Vaginosis
"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.
Clinical Context
BV, which is characterized by the loss of normal vaginal flora and an increased prevalence of anaerobic bacteria, is associated with several gynecologic conditions and adverse pregnancy outcomes, notably preterm birth. It is 3 times as common in black women vs white women.
Similarly, vitamin D deficiency is far more prevalent in black women vs white women, in part because of their skin pigmentation preventing adequate cutaneous synthesis of cholecalciferol from casual exposure to sunlight. Vitamin D is known to have immunologic effects, but vitamin D deficiency has not been previously studied in relationship to BV.
Study Highlights
- The objective of this pregnancy cohort study was to evaluate the association between maternal vitamin D status and the prevalence of BV in the first trimester.
- Serum 25(OH)D was measured with a DiaSorin radioimmunoassay kit (DiaSorin; Vercelli, Italy), which detects 100% of 25(OH)D2 and 25(OH)D3 concentrations.
- BV was diagnosed from Gram stain vaginal smears that were interpreted by Nugent's method and scored from 7 to 10.
- The study cohort consisted of 469 women who had a pelvic examination and blood sampling for measurement of serum 25(OH)D levels before 16 weeks' gestation.
- BV was diagnosed in approximately 41% of women.
- More than half (52%) of women had serum 25(OH)D levels of less than 37.5 nmol/L.
- Women with BV had a lower mean unadjusted serum 25(OH)D concentration vs those with normal vaginal flora (29.5 nmol/L; 95% CI, 27.1 - 2.0 vs 40.1 nmol/L; 95% CI, 37.0 - 43.5; P < .001).
- The prevalence of BV decreased with increasing vitamin D levels (P < .001).
- Approximately 57% of women with a serum 25(OH)D concentration of less than 20 nmol/L had BV vs 23% of those with a serum 25(OH)D concentration of more than 80 nmol/L.
- There was a dose-response association between 25(OH)D levels and the prevalence of BV.
- BV prevalence decreased as 25(OH)D levels increased to 80 nmol/L, and it then plateaued at higher 25(OH)D levels.
- Serum 25(OH)D concentration of 20 nmol/L was associated with a 1.65-fold (95% CI, 1.01 - 2.69) increase in the prevalence of BV, after adjustment for race and sexually transmitted diseases.
- Serum 25(OH)D concentration of 50 nmol/L was associated with a 1.26-fold (95% CI, 1.01 - 1.57) increase in the prevalence of BV, after adjustment.
- Vitamin D deficiency was strongly associated with BV in black women but not in white women.
- This racial difference was attributed to black women being overrepresented in the lower range of 25(OH)D, where there was a strong log-linear association between vitamin D status and BV risk, and white women being overrepresented in the upper range of 25(OH)D status.
- The investigators concluded that vitamin D deficiency is associated with BV and may contribute to the strong racial disparity in the prevalence of BV.
- Limitations of the study include small number of women with optimal vitamin D status, cross-sectional analysis, unmeasured or unknown confounders, and lack of data on parathyroid hormone concentrations or other markers of vitamin D status.
Clinical Implications
- In a pregnancy cohort study, women with BV before 16 weeks' gestation had a lower mean unadjusted serum 25(OH)D concentration vs those with normal vaginal flora.
- The prevalence of BV decreased with increasing serum 25(OH)D levels, and vitamin D deficiency was strongly associated with BV in black women but not in white women, suggesting that vitamin D deficiency is associated with BV and may contribute to the strong racial disparity in the prevalence of BV.
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