Effects of Vitamin D Supplementation on General and Central Obesity: Results from 20 Randomized Controlled Trials Involving Apparently Healthy Populations

Background:The obesity pandemic has been paralleled by a high prevalence of vitamin D deficiency (VDD). There is growing epidemiological evidence linking low vitamin D status with obesity events. In addition, observational studies also show that obesity may increase the risk of VDD. However, there is insufficient knowledge to understand whether there is a causality between the two. Moreover, the impact of vitamin D supplementation on obesity indices has shown inconsistent outcomes.Objective:This meta-analysis aimed to assess whether vitamin D supplementation modified general and central obesity indices in apparently healthy populations.Methods:A systematic retrieval of relevant randomized controlled trials (RCTs) was undertaken using Pubmed, Embase, Web of Knowledge and Chinese National Knowledge Infrastructure databases. The pooled weighted mean difference (WMD) and 95% confidence intervals (CI) were used to assess the changes in body mass index (BMI), waist circumference (WC), waist-to-hip ratio (WHR) and 25-hydroxyvitamin D (25[OH]D) from baseline.Results:Twenty RCTs involving 3,153 participants reporting either BMI, WC, WHR or 25(OH)D met the inclusion criteria. When compared with placebo, vitamin D supplementation had no significant decreases in BMI (WMD = -0.09 kg/m(2), 95% CI -0.19 to 0.01,p= 0.08), WC (WMD = -0.71 cm, 95% CI -1.58 to 0.16,p= 0.112) or WHR (WMD = 0.00, 95% CI -0.01 to 0.01,p= 0.749). However, in the subgroups of females, Asia region studies and intervention duration >= 6 months, a beneficial and significant reduction in BMI and WC was noted (allp< 0.026). On the other hand, pooled results showed that there was a significant increase in serum 25(OH)D levels (WMD = 13.20 ng/mL, 95% CI 9.83-16.58,p< 0.001) after vitamin D intervention. No publication bias was found in our study.Conclusions:Overall, supplementation with vitamin D produced no significant effect on the BMI, WC or WHR of healthy adults.