Mild activity, walking reduce hip fracture risk for postmenopausal women
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Regular, weekly physical activity such as walking and yard work can lower the risk for hip or total fracture among postmenopausal women, according to findings published in JAMA Network Open.
“Our study found that mild physical activity and walking were associated with lower risk of hip fracture in older women,” Michael J. LaMonte, PhD, MPH, a research associate professor in the department of epidemiology and environmental health at the University of Buffalo, New York, and colleagues wrote. “This is an important and relatively novel finding. To date, there has been insufficient evidence available to support recommending lighter intensity activities as part of public health guidelines. If other studies confirm our results showing that light-intensity activity is associated with fracture benefit, there could be basis for a future guideline recommendation.”
LaMonte and colleagues analyzed data from 77,206 postmenopausal women aged 50 to 79 years enrolled in the Women’s Health Initiative between 1993 and 1998 at 40 U.S. clinical centers (mean age, 63 years; 85.6% white; 8.4% with osteoporosis; 3.9% prescribed osteoporosis therapies). Women self-reported physical activity and sedentary time, such as days per week and duration (minutes) of usual mild, moderate and strenuous recreational physical activity. Researchers summarized physical activity as energy expenditure, calculated as the product of metabolic equivalent (MET) intensity values for each activity multiplied by the hours per week of reported participation, or MET hours per week. Standard MET values were assigned to mild (3 METs), moderate (4.5 METs), and strenuous (7 METs) activity, as well as four walking speeds, heavy chores and yard work. Researchers observed participants for outcomes through September 2015 and used Cox proportional hazards models to estimate HRs for associations between physical activity and incident fracture.
During a mean follow-up of 14 years, 25,516 women (33.1%) reported experiencing at least one fracture.
Compared with inactive women, defined as 0 MET hours per week, HRs for total fracture were 0.94 for women with less than 7.5 MET hours per week (95% CI, 0.9-0.98), 0.95 for women with 7.5 to 17.7 MET hours per week (95% CI, 0.91-0.99) and 0.94 for women with more than 17.7 MET hours per week (95% CI, 0.9-0.98). Women in the highest total physical activity tertile were 18% less likely to experience a hip fracture during follow-up compared with inactive women (HR = 0.82; 95% CI, 0.72-0.95). Women were also less likely to experience a hip fracture during follow-up with walking at “fairly fast” speeds (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 = 0.9; 95% CI, 0.82-0.99) when compared with inactive women.
Total physical activity greater than 17.7 MET hours per week was positively associated with knee fracture vs. no activity (HR = 1.26; 95% CI, 1.05-1.5), whereas mild activity was associated with lower risk for clinical vertebral fracture (HR = 0.87; 95% CI, 0.78-0.96) and total fractures (HR = 0.91; 95% CI, 0.87-0.94). Moderate to vigorous activity was positively associated with wrist or forearm fracture (HR = 1.09; 95%CI, 1.03-1.15).
In analyses examining nonrecreational activity, researchers found that more than 6 MET hours per week of yard work was associated with lower risk for total fracture (HR = 0.95; 95% CI, 0.92-0.98) and hip fracture (HR = 0.9; 95% CI, 0.82-0.99) when compared with no yard work.
In age-adjusted analyses assessed sedentary time, 9.5 hours of daily sitting or lying down was associated with greater risk for hip fracture (HR = 1.11; 95% CI, 1.01-1.21), vertebral fracture (HR = 1.09; 95% CI, 1.01-1.17) and total fracture (HR = 1.1; 95% CI, 1.07-1.13).
“The current results suggest that lower-intensity activities, including walking and nonrecreational activities, could have benefit on fracture risk at older ages,” the researchers wrote. “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. Sedentary behavior as an independent factor predisposing individuals to fracture requires further investigation.” – by Regina Schaffer
Disclosures: The authors report no relevant financial disclosures.
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Douglas P. Kiel, MD, MPH
This is certainly a large study of older adult women that speaks favorably about the importance of physical activity on fracture risk.
The study involved a lot of women, the women were well characterized and the study used standardized instruments, along with careful fracture adjudication for hip fractures. Another strength was the adjustment for potential confounding variables. One of the main weaknesses was the inability to confirm self-reported fractures at other sites using medical records, therefore, some fractures many not be accurately recalled. Thus, the findings that physical activity increased some fractures, such as at the forearm and knee, while decreasing others is difficult to explain and may have arisen because of these limitations.
The second limitation is, of course, the study design, which is observational and not a randomized controlled trial. The best type of evidence for physical activity reducing fractures would be a randomized, placebo-controlled trial. Unfortunately, we may never see a large randomized trial assessing the impact of physical activity on fracture risk; however another way to get at this question with avoidance of potential bias is to perform a Mendelian randomization analysis. This is a novel way to connect a lifestyle practice, such as physical activity, with an outcome like fracture.
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