Bolland and colleagues have written a lovely summary of the evidence on the effects of vitamin D supplements, with or without calcium, on health. Their careful and comprehensive systematic overview based on a large sample, and providing narrow confidence limits, finds that there is no evidence that vitamin D, with or without calcium, reduces the risk of fractures in elderly people with no known bone disease. It is, as expected, efficacious in people with established osteomalacia. Systematic reviews of lower quality or based on per protocol analyses, tend to find the more optimistic results, but the data, taken in the round, yield a null result. The reviewers find that additional research is unlikely to further clarify the issue, as an effect of more than a 10% reduction in fracture has been ‘excluded’ by the existing studies. From a Bayesian perspective, further data are unlikely to have much effect on credible limits. The studies do not find any evidence that calcium plus vitamin D have either harmful or beneficial effects on the other (non-skeletal) outcomes, such as cancer or heart disease. Perhaps this is an example of the horizon of science; science cannot prove a null result, merely exclude a positive or negative effect beyond certain limits. We will never know everything, but let’s just forget about the use of vitamin D and calcium as prophylaxis in healthy people as any benefit must be nugatory – less than 10% relative risk reduction, which equates to a very small absolute reduction.
— Richard Lilford, CLAHRC WM Director
- Bolland MJ, Leung W, Tai V, et al. Calcium intake and risk of fracture: systematic review. BMJ. 2015; 350: h4580.