Figures from the newly published meta-analysis suggest that 54% of pregnant women are at risk from BV but the potential infection rate is higher among black women (56%) and increases sharply in the first trimester to 122%.
Vitamin D receptors (VDRs) are implicated in vaginal homeostasis; they regulate cell production and diversity, including vaginal epithelium, and modulate the PH of the vaginal microbial environment, although the exact mechanism is not well established, researchers write in Nutrition.
The recent report states: “Vitamin D is linked to diverse immunomodulatory actions, including the enhancement of the innate immune system and regulation of the adaptive immune responses, through binding to VDRs expressed by a number of different immune cell subsets.”
Deficiencies reduce antimicrobial peptide synthesis and anti-inflammatory cytokine production, while increasing pro-inflammatory expression to promote BV incidence, they explain.
“Considering the high prevalence and adverse health outcomes of vitamin D deficiency and BV, these findings have potential clinical implications,” adds the report.
Causal link
Six of the 14 studies evaluated found no relationship between vitamin D deficiency and BV prevalence in pregnancy, however eight confirmed a positive association and led researchers to return a causal link.
“By elevating calcium concentration, vitamin D may stimulate insulin secretion and increase glycogen synthesis, which induces glycogen deposition in the vagina. Therefore, vitamin D deficiency may alter glucose homeostasis in the vagina and enhance BV prevalence,” they comment.
Subgroup analyses revealed similar empirical trends after adjustments for confounders, and also identified a statistical association between vitamin D deficiency and BV risk in white women.
Race disparity
The authors suggest the higher infection risk among black women was possibly due to dark skin pigmentation that may inhibit conversion from 7-dehydrocholesterol (provitamin D3) to pre-calciferol (pre-vitamin D3 form) following sun exposure.
“The potential reason may be that most black women usually suffer from a higher burden of vitamin D deficiency than white women. Additionally, vitamin D intake from diet and supplementation for black women is relatively low,” the authors write.
Equally, lifestyle factors, such as smoking, are known risk factors and likely to vary among races. “These findings suggest that race is not an independent factor for BV occurrence,” they add.
Overall findings support comparable studies that report the efficacy of vitamin D treatment to eliminate asymptomatic BV in non-pregnant women, they conclude, but assert that further studies are needed to clarify the relationship between race and BV.
Study strategy
Source material was obtained from PubMed, Embase, Cochrane Library, and Web of Science and comprised 14 studies from 13 articles, including 4,793 participants.
All research focused on the effects of vitamin D intake during pregnancy and the odds ratio (OR), relative risk (RR), or hazard ratio with 95% confidence interval (CI) of BV risk. The risk of bias was evaluated using the Newcastle-Ottawa Scale (NOS) scoring system.
Statistical and sensitivity analyses were performed to determine the strength of association between vitamin D deficiency and risk of BV and identify subgroup variations.
Source: Frontiers in Nutrition
Published online, November 22, 2022: http://doi.org/10.3389/fnut.2022.2026592
‘Vitamin D deficiency increases the risk of bacterial vaginosis during pregnancy: Evidence from a meta-analysis based on observational studies’
Authors: Lirong Ma, Zhuoran Zhang, Liyang Li, Lijie Zhang, Zhijuan Lin and Hao Qin