Effect of vitamin D supplementation alone or with calcium on adiposity measures: a systematic review and meta-analysis of randomized controlled trials.

Systematic review and meta-analysis of randomized controlled trials in adults aged 18 years and older. The analysis included 42,430 participants across 26 trials conducted in multiple countries and examined end-of-study adiposity outcomes, including BMI, weight, and fat mass.

Across 26 randomized controlled trials, adults received vitamin D supplementation alone or vitamin D combined with calcium. Most trials used vitamin D3, with doses ranging from 400 to 5714 per day in the examples reported; some trials used calcium co-supplementation at about 200 to 1500 mg/day, and a small number involved vitamin D2 or alphacalcidiol.

Vitamin D supplementation, with or without calcium, did not meaningfully reduce adiposity in adults. For vitamin D alone versus placebo, BMI was WMD −0.06 (−0.14 to 0.03), weight was WMD −0.05 (−0.32 to 0.23), and fat mass was WMD −0.43 (−1.69 to 0.84), with p = 0.20. For vitamin D plus calcium versus calcium control, BMI was WMD 0.02 (−0.11 to 0.14), weight was WMD 0.12 (−0.24 to 0.49), and fat mass was WMD 0.12 (−0.22 to 0.45), with p = 0.80. No dose-response relationship was found, and the authors concluded that more adequately powered trials with baseline vitamin D assessment and objective adiposity measures are needed.

The included trials used heterogeneous vitamin D formulations and doses, with varying calcium cointerventions, which limits comparability. Baseline vitamin D status and objective adiposity assessment were not consistently available, and fat mass showed substantial heterogeneity in the vitamin D alone versus placebo comparison (I2 81.2%). Per-arm sample sizes were not reported in the provided text, limiting assessment of precision at the individual trial-arm level.