title: The association between physical activity and osteoporotic fractures: a review of the evidence and implications for future research.
abstract: OBJECTIVE
  Physical activity helps maintain mobility, physical functioning, bone mineral density (BMD), muscle strength, balance and, therefore, may help prevent falls and fractures among the elderly. Meanwhile, it is theoretically possible that physical activity increases risk of fractures as it may increase risk of falls and has only a modest effect on BMD. This review aims to assess the potential causal association between physical activity and osteoporotic fractures from an epidemiological viewpoint.
  
  
  METHODS
  As the medical literature lacks direct evidence from randomized controlled trials (RCTs) with fracture end points, a meta-analysis of 13 prospective cohort studies with hip fracture end point is presented. The current evidence base regarding the link between exercise and fracture risk determinants (namely, falls, BMD, and bone quality) are also summarized.
  
  
  RESULTS
  Moderate-to-vigorous physical activity is associated with a hip fracture risk reduction of 45% (95% CI, 31-56%) and 38% (95% CI, 31-44%), respectively, among men and women. Risk of falling is suggested to be generally reduced among physically active people with a potential increased risk in the most active and inactive people. Positive effects of physical activity on BMD and bone quality are of a questionable magnitude for reduction of fracture risk.
  
  
  CONCLUSIONS
  The complexity of relationship between physical activity and osteoporotic fractures points out to the need for RCTs to be conducted with fractures as the primary end point.
authors.affiliation: Department of Public Health and Primary Care, Institute of Public Health, University of Cambridge, Cambridge, UK. am700@cam.ac.uk
authors.forename: Alireza
authors.initials: A
authors.lastname: Moayyeri
mesh_terms: D000058:Accidental Falls / Q000517:prevention & control; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D015519:Bone Density; D015444:Exercise; D005260:Female; D006620:Hip Fractures / Q000209:etiology* / Q000517:prevention & control*; D006801:Humans; D008297:Male; D008875:Middle Aged; D010024:Osteoporosis / Q000150:complications*; D012307:Risk Factors