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 D-3 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 subcohort 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 x 2 factorial design of supplemental vitamin D-3 (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 D-3 vs 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 D 3 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 D-3 supplementation vs placebo in the general older population did not improve weight or body composition. Whether supplemental vitamin D-3 may benefit individuals with normal BMI warrants further study.