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The Effects of Age, Adiposity, and Physical Activity on the Risk of 7 Site-Specific Fractures in Postmenopausal Women.

Lacombe J, Cairns BJ, Green J, Reeves GK, Beral V, Armstrong ME; Million Women Study Collaborators.

J Bone Miner Res 2016;31:1559-68.

Risk factors for fracture of the neck of the femur are relatively well established, but those for fracture at other sites are little studied. In this large population study we explore the role of age, body mass index (BMI), and physical activity on the risk of fracture at 7 sites in postmenopausal women. As part of the Million Women Study, 1,154,821 postmenopausal UK women with a mean age of 56.0 (SD 4.8) years provided health and lifestyle data at recruitment in 1996-2001. All participants were linked to National Health Service hospital records for day-case or overnight admissions with a mean follow-up of 11 years per woman. Adjusted absolute and relative risks for 7 site-specific incident fractures were calculated using Cox regression models. During follow-up, 4931 women had a fracture of the humerus, 2926 of the forearm, 15,883 of the wrist, 9887 of the neck of the femur, 1166 of the femur (not neck), 3199 a lower leg fracture, and 10,092 an ankle fracture. Age-specific incidence rates increased gradually for fractures of forearm, lower leg, ankle and femur (not neck), and steeply for fractures of neck of femur, wrist, and humerus. When compared to women with desirable BMI (20.0-24.9 kg/m2 ), higher BMI was associated with a reduced risk of fracture of the neck of femur, forearm and wrist, but an increased risk of humerus, femur (not neck), lower leg and ankle fractures (p < 0.001 for all). Strenuous activity was significantly associated with a decreased risk of fracture of the humerus and femur (both neck and rest of femur) (p < 0.001), but was not significantly associated with lower leg, ankle, wrist and forearm fractures. Postmenopausal women are at a high lifetime risk of fracture. BMI and physical activity are modifiable risk factors for fracture, but their associations with fracture risk differ substantially across fracture sites.