title: Need for additional calcium to reduce the risk of hip fracture with vitamin d supplementation: evidence from a comparative metaanalysis of randomized controlled trials.
abstract: OBJECTIVE
  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.
  
  
  METHODS
  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.
  
  
  METHODS
  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.
  
  
  METHODS
  Independent extraction was performed by two authors using predefined criteria, including study quality indicators.
  
  
  RESULTS
  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.
authors.affiliation: Leuven University Center for Metabolic Bone Diseases, Katholieke Universiteit Leuven, Belgium, and Brigham and Women's Hospital, Boston, MA 02115, USA. steven.boonen@uz.kuleuven.ac.be
authors.forename: Steven
authors.initials: S
authors.lastname: Boonen
authors.forename: Paul
authors.initials: P
authors.lastname: Lips
authors.forename: Roger
authors.initials: R
authors.lastname: Bouillon
authors.forename: Heike A
authors.initials: HA
authors.lastname: Bischoff-Ferrari
authors.forename: Dirk
authors.initials: D
authors.lastname: Vanderschueren
authors.forename: Patrick
authors.initials: P
authors.lastname: Haentjens
mesh_terms: D002118:Calcium / Q000627:therapeutic use*; D019587:Dietary Supplements; D006620:Hip Fractures / Q000517:prevention & control*; D006801:Humans; D008875:Middle Aged; D010024:Osteoporosis; D017698:Postmenopause; D016032:Randomized Controlled Trials as Topic; D012306:Risk; D014807:Vitamin D / Q000627:therapeutic use*
chemical_list: D014807:Vitamin D; D002118:Calcium