Physical activity and osteoporotic fracture risk in older women

Background: Physical activity has been related to enhanced bone mass and improved physical functioning and thus may reduce the risk for osteoporotic fracture. Objective: To determine whether higher levels of physical activity are related to lower incidence of hip, wrist, and vertebral fractures. Design: Prospective cohort study. Setting: Four clinical centers in Baltimore, Maryland; Portland, Oregon; Minneapolis, Minnesota; and the Monongahela Valley, Pennsylvania. Participants: 9704 nonblack women 65 years of age or older. Measurements: Physical activity was assessed by questionnaire at baseline. Hip and wrist fractures were followed for an average of 7.6 years. The incidence of vertebral fracture was determined morphometrically by using radiography at baseline and an average of 3.7 years later. Results: Higher levels of leisure time, sport activity, and household chores and fewer hours of sitting daily were associated with a significantly reduced relative risk for hip fracture after adjustment for age, dietary factors, falls at baseline, and functional and health status. Very active women (fourth and fifth quintiles) had a statistically significant 36% reduction in hip fractures (relative risk, 0.64 [95% CI, 0.45 to 0.89]) compared with the least active women (lowest quintile). The intensity of physical activity was also related to fracture risk: Moderately to vigorously active women had statistically significant reductions of 42% and 33% in risk for hip and vertebral fractures, respectively, compared with inactive women. Total physical activity, hours of household chores per day, and hours of sitting per day were not significantly associated with wrist or vertebral fractures. Conclusions: Among older community-dwelling women, physical activity is associated with a reduced risk for hip fracture but not wrist or vertebral fracture.