Postmenopausal women who participate in vigorous physical activity have a lower risk of total and hip fractures, but higher knee fracture risk, say researchers recently writing in JAMA Network Open.
Approximately 1.5 million fractures occur annually in women who live in the U.S., with around 14 percent of fractures occurring in the hip, an injury that has a mortality as high as 20 percent. Physical activity is inversely associated with hip fracture risk in older women, but the association of physical activity with fracture at other sites remains unclear. Meanwhile, sedentary behavior is becoming an established modifiable risk factor for major forms of morbidity and mortality, independent of physical activity habits, but its contribution to fracture has not been systematically evaluated.
“The Women’s Health Initiative is a prospective cohort study among postmenopausal women with ongoing assessment of fractures. We examined recreational physical activity, household activities, walking, and sedentary behavior in association with incident fracture and the extent to which age, race/ethnicity, or fall frequency modified this association in older, community-dwelling, ambulatory women,” wrote the authors of the study, led by Jean Wactawski-Wende, Ph.D., of The State University of New York in Buffalo.
Between October 1993 and December 1998, the study enrolled 77,206 postmenopausal women (mean age, 63.4 years; 85.6 percent white) at 40 U.S. clinical centers. Participants were observed for total and site-specific fracture incidence through September 2015.
During a mean follow-up period of 14 years, 33.1 percent of the women reported a first incident fracture. Total physical activity was inversely associated with the adjusted risk of hip fracture (>17.7 metabolic equivalent [MET] hours/week vs none: HR, 0.82; 95% CI, 0.72-0.95). Lower hip fracture rates were also observed for walking (HR, 0.88; 95% CI, 0.78-0.98), mild activity (HR, 0.82; 95% CI, 0.73-0.93), moderate to vigorous activity (HR, 0.88; 95% CI, 0.81-0.96), and yard work (HR, 0.90; 95% CI, 0.82-0.99).
Increased fracture risk was evident between knee fracture and total physical activity (>17.7 MET hours/week vs none: HR, 1.26; 95% CI, 1.05-1.50) and moderate to vigorous activity was positively associated with wrist or forearm fracture (HR, 1.09; 95% CI, 1.03-1.15). Mild activity was associated with lower risks of clinical vertebral fracture (HR, 0.87; 95% CI, 0.78-0.96) and total fractures (HR, 0.91; 95% CI, 0.87-0.94).
“Mild activity and walking were associated with lower hip fracture risk, a finding with important public health implications because these activities are common in older adults.” the authors wrote.
After controlling for total physical activity, sedentary time was positively associated with total fracture risk (>9.5 hours/d=day vs <6.5 hours/day: HR, 1.04; 95% CI, 1.01-1.07). When analyzed jointly, higher total activity reduced some of the total fracture risk associated with sedentary behavior.
“Lower-intensity activities, including walking and nonrecreational activities, could have benefit on fracture risk at older ages. If confirmed, future recommendations on fracture prevention in postmenopausal women should promote light physical activity, especially in those who are frail and unable to safely engage in more intense activities,” the authors wrote.
Sedentary behavior as an independent factor predisposing postmenopausal women to fracture requires further investigation.
Michael J. LaMonte, Jean Wactawski-Wende, Joseph C. Larson, et al. “Association of Physical Activity and Fracture Risk Among Postmenopausal Women.” JAMA Network Open. October 25, 2019. doi:10.1001/jamanetworkopen.2019.14084