WHI study: Light activity reduces fracture risk

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A new analysis of data from the Women’s Health Initiative (WHI) suggests that older women who do regular physical activity-even just walking-have a lower risk of fracture than their peers who are sedentary. The findings were published in JAMA Network Open.

Methods
The prospective WHI cohort included more than 77,000 postmenopausal women aged 50 to 79 who were enrolled at 40 US clinical centers between October 1993 and December 1998. Participants were observed for outcomes through September 2015 and data analysis was performed from June 2017 to August 2019. For the new research, the authors assessed the impact of physical activity and sedentary behavior on fracture incidence in postmenopausal women. 

The participants self-reported their activity levels on questionnaires that asked how many days per week they did mild, moderate, and strenuous physical activity and for how long. Mild physical activity was defined as slow dancing, bowling, or golf. Activities considered moderate were biking outdoors, using an exercise machine, calisthenics, easy swimming, or popular or folk dancing. Exercise that resulted in sweating and a fast heartbeat (e.g., aerobics, aerobic dancing, jogging, tennis, or swimming laps) was considered strenuous. 

Separate questions were asked about walking, such as “how often do you walk outside the home for more than 10 minutes without stopping. Other specific questions were asked about nonrecreational activities, such as how many hours were spent per week on scrubbing floors and yard work. Participants also self-reported how many hours per day and night they spent doing sedentary activities like sitting, watching television, or lying down. 

The authors used standard metabolic equivalent (MET) intensity values to calculate energy expenditures for the participants’ activity levels. Mild activities were considered to be 3.0 METs whereas as moderate activities were 4.5 METs and strenuous activities were 7.0 METs. Walking speeds, heavy chores, and yard work were also assigned METs.

Results
Based on a mean follow-up period of 14.0 years, the researchers found that total physical activity was inversely associated with the multivariable-adjusted risk of hip fracture (> 17.7 MET h/wk vs none: HR, 0.82; 95% CI, 0.72-0.95; P for trend < .001). Inverse associations with hip fracture were also observed for walking (> 7.5 MET hr/wk vs none; HR, 0.88; 95% CI, 0.78-0.98; P for trend = .01), mild activity (HR, 0.82; 95% CI, 0.73-0.93; P for trend = .003), moderate to vigorous activity (HR, 0.88; 95% CI, 0.81-0.96); P for trend = .002) and yard work (HR, 0.90; 95% CI, 0.82-0.99; P for trend = .04). 

Mild activity was associated with lower risks of clinical vertebral fracture (HR, 0.87; 95% CI, 0.78-0.96; P for trend = .006) and total fractures (HR, 0.91; 95% CI, 0.87-0.94; P for trend < 0.01). Moderate to vigorous activity was positively associated with wrist or forearm fracture (HR, 1.09; 95% CI, 1.03-1.15; P for trend = .004). After controlling for covariates such as age, history of fracture after age 55 and bone drug use, and total physical activity, sedentary time was positively associated with total fracture risk (> 9.5 h/d vs < 6.5 h/d: HR, 1.04; 95% CI, 1.01-1.07; P for trend = .01). When analyzed jointly, higher total activity mitigated some of the total fracture risk associated with sedentary behavior. 

Conclusion
Noting that there is the most comprehensive evaluation to date of physical activity and fracture incidence in older women, the authors concluded that “current results suggest that lower-intensity activities, including walking and nonrecreational activities, could have benefit on fracture risk at older ages.” They believe that if their results are confirmed, light physical activity should be recommended to postmenopausal women to prevent fracture, particular those who cannot safely undertake more intense activity.