Do vitamin D supplements help prevent respiratory tract infections?

A clinically useful effect remains uncertain despite hints in a new analysis

Vitamin D supplementation is a hot topic, provoking passionate arguments for and against widespread supplementation. Recently in The BMJ we discussed the evidence, concluding that vitamin D supplements should not be taken by adults to prevent non-musculoskeletal disease. Three months later comes a meta-analysis by Martineau and colleagues (doi:10.1136/bmj.i6583), concluding that prevention of acute respiratory tract infection is a “major new indication for vitamin D supplementation." Given the short time between articles, why are the conclusions so different? Is this really a major new development, providing the long sought reliable evidence of benefits of vitamin D on a non-skeletal outcome in the general population? Or is it yet another hypothesis about vitamin D supplementation that needs testing in adequately powered randomised controlled trials?