Need for additional calcium to reduce the risk of hip fracture with vitamin d supplementation: evidence from a comparative metaanalysis of randomized controlled trials.

PURPOSE

The purpose of this study was to extend the metaanalysis of Bischoff-Ferrari et al., which found that 700-800 IU/d vitamin D reduced hip fracture risk in elderly individuals by 25%, by defining the need for additional calcium supplementation in individuals receiving vitamin D for the prevention of hip fractures.

DATA SOURCES

MEDLINE and EMBASE.com (search terms: "vitamin D" and "hip fracture"), bibliographies of articles retrieved, and the authors' reference files were used as data sources.

STUDY SELECTION

Selected studies were randomized controlled trials (RCTs) of oral vitamin D with or without calcium supplementation vs. placebo/no treatment in postmenopausal women and/or older men (>or=50 yr) specifically reporting a risk of hip fracture.

DATA EXTRACTION

Independent extraction was performed by two authors using predefined criteria, including study quality indicators.

DATA SYNTHESIS

All pooled analyses are based on random-effects models. Based on four RCTs (9083 patients), the pooled relative risk (RR) of hip fracture for vitamin D alone was 1.10 [95% confidence intervals (CI) 0.89, 1.36]. No between-trial heterogeneity was observed. For the six RCTs (45,509 patients) of vitamin D with calcium supplementation, the pooled RR for hip fracture was 0.82 (95% CI 0.71, 0.94). There was no heterogeneity between trials. In an adjusted indirect comparison of the summary RRs from the two metaanalyses, the RR for hip fracture for vitamin D with calcium vs. vitamin D alone was 0.75 (95% CI 0.58, 0.96).

CONCLUSIONS

Our analyses, designed to extend the findings of Bischoff-Ferrari et al., suggest that oral vitamin D appears to reduce the risk of hip fractures only when calcium supplementation is added.