Vitamin D status in endometriosis: a systematic review and meta-analysis

Purpose No consensus exists on the relationship between vitamin D status and endometriosis. The chief aim of our study was to evaluate the association between serum vitamin D levels and endometriosis. Methods We searched for MEDLINE, EMBASE, and China National Knowledge Infrastructure (CNKI) databases for studies elucidated the circulating vitamin D levels in endometriosis. The standardized mean differences (SMDs) or odds ratios (ORs) with their 95% confidence interval (CIs) were calculated to evaluate the association between vitamin D levels and endometriosis. Results Nine studies were included in this meta-analysis. The pooled results indicated that women with endometriosis had lower vitamin D status than that in controls (SMD - 0.97 ng/mL, 95% CI - 1.80 to - 0.14; p = 0.02), and vitamin D status had a negative correlation with the severity of the disease (stage III-IV vs stage I-II: SMD - 1.33 ng/mL, 95% CI - 2.54 to - 0.12; p = 0.03). Although it was not statistically significantly different, hypovitaminosis D had a tendency to be associated with endometriosis (OR 2.77, 95% CI 0.85-6.08, p = 0.10). Heterogeneity was high among included studies. Subgroup analyses revealed that women with no hormone use had lower vitamin D status when compared with controls (SMD - 1.38 ng/mL, 95% CI - 2.59 to - 0.18; p = 0.02). For studies which sample size < 100, serum vitamin D levels were significantly lower in patients than that in controls (SMD - 0.65 ng/mL, 95% CI - 1.19 to - 0.11; p = 0.02). Conclusions Women with endometriosis had lower vitamin D status when compared with controls, and a negative relationship between vitamin D levels and severity of endometriosis was observed. In addition, hypovitaminosis D was a potential risk factor for endometriosis.