Numerous observational studies and randomised trials have observed that optimal vitamin D status has a positive effect on our health and may reduce cancers and cardiovascular diseases. However, a number of systematic reviews and meta-analyses on vitamin D for prevention of mortality have reported variable results.
This systematic review analysed the influence of different forms of vitamin D on mortality. In the 50 trials that provided data for our analyses a total of 94,148 participants were randomly assigned to either vitamin D or no treatment or a placebo. All trials came from high-income countries. The mean age of participants was 74 years. The mean proportion of women was 79%. The median duration of vitamin D administration was two years. Our analyses suggested that vitamin D3 reduces mortality by about 6%, which corresponds to 200 participants that need to be treated over a median of two years to save one additional life. Another supplemental form of vitamin D, vitamin D2 (ergocalciferol), as well as the active forms of vitamin D (alfacalcidol and calcitriol) had no significant effect on mortality. We also found evidence of adverse effects including renal stone formation (seen for vitamin D3 combined with calcium) and elevated blood levels of calcium (seen for both alfacalcidol and calcitriol). In conclusion, we found evidence that vitamin D3 decreases mortality in predominantly elderly women who are mainly in institutions and dependent care.