Effects of Vitamin D3 Supplementation on Body Composition in the VITamin D and OmegA-3 TriaL (VITAL)

Context Although observational studies show inverse associations between vitamin D status and body weight/adiposity, there are few large randomized controlled trials (RCTs) investigating this relationship. Objective To determine whether vitamin D3 supplementation lowers weight or improves body composition. Design The VITamin D and OmegA-3 TriaL (VITAL) was a double-blinded, placebo-controlled RCT including 25 871 US adults. This ancillary study was completed in a sub-cohort that underwent body composition assessments at baseline and 2-year follow-up (89% retention). Setting Harvard Clinical and Translational Science Center in Boston. Participants 771 participants (men ≥ 50 and women ≥ 55 years). Interventions 2 × 2 factorial design of supplemental vitamin D3 (2000 IU/day) and/or omega-3 fatty acids (1 g/day). Main Outcome Measures Endpoints were 2-year changes in weight, body mass index (BMI), waist circumference, and total and/or regional fat and lean tissue measures determined by dual-energy X-ray absorptiometry. Effect modification by clinical variables and total and free 25-hydroxyvitamin D (25[OH]D) levels was explored. Results There were no effects of supplemental vitamin D3vs placebo on weight, BMI, or measures of adiposity and lean tissue. Effects did not vary by sex, race/ethnicity, fat mass index, or baseline total or free 25(OH)D levels. Vitamin D3 supplementation did slightly improve body fat percentage in participants with normal BMI at baseline, but not in the overweight or obese (P for interaction = 0.04). Conclusions Daily vitamin D3 supplementation vs placebo in the general older population did not improve weight or body composition. Whether supplemental vitamin D3 may benefit individuals with normal BMI warrants further study.