Physical activity, bone density, and fragility fractures in women

Sammanfattning: Scandinavia has among the highest incidence of fragility fractures in the world. The reasons for this are unknown, but might involve differences in genetic and/or environmental factors, such as sunlight exposure and levels of physical activity. Weight-bearing exercise is thought to have a beneficial effect on bone health in the young, but few studies have evaluated whether exercise in older subjects affects bone density and protects against fragility fractures.The initial objective of this thesis was to evaluate whether a combined weight-bearing training programme twice a week would be beneficial as regards bone mineral density (BMD) and neuromuscular function in older women. Forty-eight community living women with a mean age of 73 years were recruited for this 12-month prospective, randomised controlled trial, and were randomly assigned to an intervention group (n=24) or a control group (n=24). The intervention group displayed significant increments in BMD at the Ward’s triangle, maximum walking speed, and isometric grip strength compared to the control group. The second objective was to investigate if training effects were retained in older women five years after the cessation of training. The 40 women who completed the first study included in this thesis were invited to take part in a follow-up assessment five years later, and 34 women (~79 years) agreed to participate. During these five years both groups had sustained significant losses in hip BMD and in all neuromuscular function tests, and the previous exercise-induced intergroup differences were no longer seen.The third and fourth objective of this thesis was to investigate whether exercise and weight-bearing leisure activities in middle-aged women are associated with a decreased risk of sustaining hip or wrist fractures at a later stage. A cohort of women participating in the Umeå Fracture and Osteoporosis (UFO) study, a longitudinal, nested case-control study investigating associations between bone markers, lifestyle, and osteoporotic fractures, was used for the purpose of this investigation. Eighty-one hip fracture cases and 376 wrist fracture cases, which had reported lifestyle data before they sustained their fracture, were identified. These cases were compared with age-matched controls identified from the same cohort. Using conditional logistic regression analysis with adjustments for height, BMI, smoking, and menopausal status, results showed that moderate frequency of leisure physical activities such as gardening and berry/mushroom picking, were associated with reduced hip fracture risk (OR 0.28; 95% CI 0.12 – 0.67), whereas active commuting (especially walking) along with dancing and snow shoveling in leisure time, reduced the wrist fracture risk (OR 0.48; 95% CI 0.27 – 0.88, OR 0.42; 95% CI 0.22 – 0.80 and OR 0.50; 95% CI 0.32 – 0.79 respectively).In summary, this thesis suggests that weight-bearing physical activity is beneficial for BMD and neuromuscular functions such as muscle strength and gait in older women, and that a physically active lifestyle, with outdoor activities, in middle age is associated with reduced risk of both hip and wrist fractures. Possible mechanisms underlying this association include improved muscle strength, coordination, and balance, resulting in a decreased risk of falling and perhaps also direct skeletal benefits.