Changes in physical activity, sedentary time, and risk of falling: The Women's Health Initiative Observational Study
Introduction
The propensity to fall increases with aging, often due to other age related issues, such as impaired vision, balance, and mental acuity (Rubenstein, 2006). Although many falls result in minor injuries, approximately 10% will result in fractures which are associated with significant morbidity and mortality in the aged (Gillespie et al., 2012). Reductions in falls among community dwelling older adults engaging exercise interventions offers hope (Gillespie et al., 2012), as does the protection against fracture with higher baseline physical activity demonstrated in the Women's Health Initiative (WHI) (Robbins et al., 2007), but overall, the association between physical activity and falls in the literature has been inconsistent (Clarke et al., 2015). Physical activity patterns over time may prove to be more predictive of falls than exercise interventions or assessment of physical activity at a single time point. Longitudinal changes in physical activity and body composition, which may mediate the falls benefit of physical activity through preservation of muscle mass (LaStayo et al., 2003), are needed to better understand their independent and joint roles in falls risk. However, because prospective studies on older adults typically do not have repeated prospective measures on these factors, they have yet to be fully explored with respect to incidence of falling.
In the United States, physical activity decreases dramatically in adulthood, stabilizing at relatively low levels in middle aged women (Caspersen et al., 2000). Low levels of physical activity have been associated with decreased muscle mass (Morley et al., 2001). Meanwhile, sedentary time, distinctly different than insufficient moderate to vigorous physical activity (Owen et al., 2010), increases with aging (Clark et al., 2010). High sedentary time may also aid in skeletal muscle decline and has been shown to be a risk factor for falling in studies with 1–2 years follow-up (Thibaud et al., 2012).
We sought to determine whether prospectively assessed physical activity patterns, including sedentary time, are associated with the risk of falling over several years and whether risk of falling is mediated by body composition. We hypothesized that decreasing physical activity over time would be associated with increased risk of falling among postmenopausal women (Fig. 1). High sedentary time was also hypothesized to increase risk of falling.
Section snippets
Study population
The WHI Study recruited postmenopausal women aged 50–79 years at 40 WHI clinical centers across the United States between 1993 and 1998 to four clinical trials and an observational study (Design of the Women's Health Initiative Clinical Trial and Observational Study, 1998, Hays et al., 2003). Only women enrolled in the observational study were included in this analysis (N = 93,676); body composition was measured in those enrolled at the Pittsburgh, PA; Birmingham, AL; and Tucson-Phoenix, AZ sites (
Results
Overall, the mean physical activity level for the cohort was 13.7 (± 14.4) MET-h/wk. at baseline, 13.6 (± 14.6) MET-h/wk. at year 3, and 13.1 (± 14.2) MET-h/wk. at year 6. The change in physical activity across the cohort was − 0.4 (± 12.4) MET-h/wk. from baseline to year 3 and − 0.9 (± 13.5) MET-h/wk. from baseline to year 6. Total sedentary time (h/day spent sitting or sleeping) was 15.0 (± 4.2) h/day at baseline, 14.7 (± 3.7) h/day at year 3 and 14.7(± 3.8) h/day at year 6. Inactive time was reduced by −
Discussion
Contrary to our hypothesis, we found that active lifestyles and increases in physical activity over time were associated with increased fall risks among postmenopausal women aged 50–79 at baseline. Although reduction in falls has been supported by several exercise interventions (Gillespie et al., 2012), the positive studies tended to include multifactorial interventions (i.e. combination of physical activity, balance training, home hazards assessment, medication assessment, technical aids,
Conclusion
Physically active lifestyles increased falling among post-menopausal women. Additional fall prevention strategies, such as balance and resistance training, should be evaluated to assist post-menopausal women in reaching or maintaining the level of aerobic activity known to prevent and manage several chronic diseases.
Disclosure statement
The authors have declared no conflicts of interest.
Funding
This work was supported by the National Cancer Institute (CA023074); and the WHI program which is funded by the National Heart, Lung, and Blood Institute, National Institutes of Health, and the U.S. Department of Health and Human Services (HHSN268201100046C, HHSN268201100001C, HHSN268201100002C, HHSN268201100003C, HHSN268201100004C, and HHSN271201100004C).
Short list of WHI investigators
Program office: National Heart, Lung, and Blood Institute, Bethesda, Maryland.
Jacques Rossouw, Shari Ludlam, Dale Burwen, Joan McGowan, Leslie Ford, and Nancy Geller.
Clinical coordinating center (Fred Hutchinson Cancer Research Center, Seattle, WA): Garnet Anderson, Ross Prentice, Andrea LaCroix, and Charles Kooperberg.
Investigators and academic centers: (Brigham and Women's Hospital, Harvard Medical School, Boston, MA) JoAnn E. Manson; (MedStar Health Research Institute/Howard University,
Transparency document
Acknowledgements
We are thankful for the contribution of the WHI investigators and staff at the clinical centers, clinical coordinating center, and project office.
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