Vitamin D and serum leptin: a systematic review and meta-analysis of observational studies and randomized controlled trials.

We aimed to investigate the potential association between vitamin D and serum leptin levels by pooling together the results from observational studies and clinical trials. A systematic literature search of PubMed, Scopus and Google Scholar was conducted up to March 2015. The analysis of observational studies was conducted on six papers that reported nine correlation coefficients using Fisher's Z and its standard error. Then, effect sizes of eligible trials were pooled using random-effects models (the DerSimonian-Laird estimator). Results of observational studies showed an inverse association between leptin and 25-hydroxyvitamin D (25(OH)D) (Fisher's Z=-0.93, 95% CI: -0.95, -0.91). After combining trials, pooled mean difference (PMD) for 25(OH)D was 24.06 ng/ml (95% CI, 17.27-30.85; P<0.001) with significant heterogeneity among studies (P<0.001; I