Conflicting evidence exists on the role of vitamin D, either alone or in combination with calcium, in reducing fractures. Some studies have shown a reduction in the risk of fractures, others have shown no effect, and one recent study found an increased risk of hip fracture.1 The best dose to use, which patients benefit most, and which fractures are most amenable to such treatment remain a clinical dilemma.

In the linked study (doi:10.1136/bmj.b5463), the DIPART (vitamin D Individual Patient Analysis of Randomized Trials) group reports an individual patient data analysis aimed at identifying factors that influence the efficacy of vitamin D or vitamin D plus calcium in reducing fractures. The study also assessed the influence of dosing regimens and the coadministration of calcium. The study looked at seven randomised controlled trials (n=68 517)—six were individually randomised and one was cluster randomised.2 It found that trials using vitamin D (low or high dose) combined with calcium reduced the overall risk of fracture (hazard ratio 0.92, 95% confidence interval 0.86 to 0.99), but that only low dose (10 μg) vitamin D combined with calcium reduced the risk of hip fracture (0.74, 0.60 to 0.91). They found no …