Twelve double-blind RCTs (n=42,279) were included in the main analysis; an additional four open trials (n=14,180) were included in sensitivity analyses.
In the primary analysis, vitamin D supplementation significantly reduced nonvertebral fractures (RR 0.86, 95% confidence interval CI 0.77, 0.96, 12 RCTs) but not hip fractures (RR 0.91, 95% CI 0.78, 1.05; eight RCTs; n=40,886). Heterogeneity was significant for both outcomes.
In trials with a received dose of 400 IU/day or more (range 482-770 IU/day), vitamin D supplementation significantly reduced both types of fracture without significant heterogeneity; for nonvertebral fracture relative risk 0.80 (95% CI: 0.72, 0.89, 9 RCTs, n=33,265), and for hip fracture relative risk 0.82 (95% CI 0.69, 0.97; five RCTs, n=31,872). Lower doses did not significantly reduce fractures. The higher dose significantly reduced nonvertebral fractures in people living in the community and in institutions and the effect was independent of calcium supplementation.
Other analyses were reported. Inspection of the Begg funnel plot suggested possible publication bias but this was not confirmed by trim-and-fill analysis.