Vitamin D

Research summary

• A large meta-analysis in the BMJ and an earlier meta-analysis both found vitamin D supplementation modestly reduces all-cause mortality, though effects are inconsistent across trial populations.
• For cancer, a dedicated randomized-trial meta-analysis and a trial-sequential meta-analysis reached more cautious conclusions, finding reduced cancer mortality in some analyses but not clearly reduced cancer incidence.
• The clearest, most consistent benefit is for bone health: meta-analyses of calcium-plus-vitamin-D supplementation show reduced fracture risk, particularly in older, deficient, or institutionalized populations, though a 2026 meta-analysis found the fracture-prevention benefit of vitamin D or calcium alone is more modest than the combination.
• Evidence in populations with kidney disease is separately reviewed and shows a similar mortality association pattern.
• Overall, the fracture-prevention case is reasonably strong for at-risk groups, while claims of broad mortality or cancer prevention in the general population remain less certain.