Background: There is a growing body of evidence on low serum vitamin-D levels and the risk of uterine leiomyomas (UL). Therefore, this systematic review and meta-analysis was conducted to investigate the association between serum vitamin D levels and UL occurrence.
Methods: Searches were systematically conducted of the electronic databases PubMed, Scopus, EMBASE, Web of Science (ISI), Cochrane library, Ovid, and Google Scholar to identify relevant studies from inception until February 6, 2020. Heterogeneity across the included studies was examined using Cochran's Q and I-square (I2). Data was pooled using random effects modeling and expressed as standardized mean differences (SMDs).
Results: Nine eligible studies with a total of 1730 participants (835 patients with UL and 895 controls) were included in the current meta-analysis. Pooled results with random effects modeling indicated that serum vitamin D levels were significantly lower in patients with UL than in the control group (n = 9, SMD = - 0.67; 95% CI, - 0.98, - 0.35, p < 0.001; I2 = 89.3%, p < 0.001). Based on the findings of subgroup analyses, it was found that the SMD values across the included studies from Asia (n = 4, SMD = - 1.20; 95% CI, - 1.45, - 0.96, p < 0.001; I2 = 30.6%, p = 0.229) were lower than those from Europe (n = 3, SMD = - 0.34; 95% CI, - 0.49, - 0.18, p < 0.001; I2 = 0.0%, p = 0.602) and Africa (n = 2, SMD = - 0.13; 95% CI, - 0.29, 0.04, p = 0.128; I2 = 0.0%, p = 0.417), although the difference was not significant in Africa. Publication year was also found to be a potential contributor's variable in the pooled SMD using the meta-regression method (t = - 3.00, p = 0.02).
Conclusions: To the best of our knowledge, the current meta-analysis showed for the first time that serum vitamin D levels were significantly lower in women with UL in selected populations.
Keywords: Meta-analysis; Systematic review; Uterine fibroid; Uterine leiomyoma; Vitamin D.