The Relationship between Serum Vitamin D Levels and Risk of Abdominal Obesity: A Systematic Review and Dose-Response Meta-Analysis of Epidemiologic Studies

Background: Although the relation of serum vitamin D levels with abdominal obesity has been investigated by previous observational studies, the results are inconsistent. In the current study, a dose-response meta-analysis was conducted on epidemiologic studies that evaluated this association in adults. Methods: We performed a systematic search of all published articles, up to May 2020, in five electronic databases. A total of 41 observational studies that reported odds ratios (ORs) or relative risks (RRs) with 95% confidence intervals (CIs) for abdominal obesity in relation to serum vitamin D levels in adults were found. Results: Meta-analysis on 36 cross-sectional studies (combining 44 effect sizes) with 257699 participants, illustrated that the highest serum vitamin D level in comparison with the lowest serum vitamin D level was significantly related to 23% decreased odds of central obesity (OR=0.77; 95%CI:0.71-0.83). This inverse association was also significant in almost all subgroups based on different covariates. Based on dose-response analysis, each 25 nmol/l increase in serum vitamin D levels, was related to 8% reduced risk of central obesity (OR=0.92;95%CI:0.85,0.99). After limiting the analysis to 23 effect sizes from 17 studies with representative population (242135 participants), the same results were obtained (OR=0.79; 95%CI: 0.71-0.87). Based on dose-response analysis on studies with representative populations, each 25 nmol/l increase in blood vitamin D levels was linked to 10% decreased central adiposity risk(OR=0.90; 95%CI: 0.82, 0.99). Conclusion: In this meta-analysis of epidemiologic studies, we demonstrated an inverse significant relation between serum vitamin D levels and risk of central obesity in adults, in a dose-response manner. The same findings were obtained in representative populations.