Abstract
BackgroundThe causal effect of physical activity on reducing dementia risk has been questioned due to the possibility of reverse causation. This study examined the potential causal effects of physical activity on reducing dementia risk using residency in a snowy area as an instrumental variable (IV) representing the physical activity of older adults.MethodsWe used cohort data from the Japan Gerontological Evaluation Study, a longitudinal cohort enrolling people aged 65 or older who were physically and cognitively independent in 2013; study participants were followed for an average of 5.7 years. Participants in the present study included 73,260 individuals living in 19 municipalities in Japan. Physical activity was measured by self-report questionnaires and the incidence of dementia was ascertained by linking participants to the public registries of long-term care insurance. IV estimation was obtained from a piecewise Cox proportional hazard model using a two-stage regression procedure.ResultsDuring the study period, we ascertained 8714 cases (11.9%) of dementia onset. In the IV analysis, we found that the frequency of physical activity per week was negatively associated with dementia risk, though the association weakened over time (Year 1: hazard ratio = 0.53, 95% confidence interval: 0.39–0.74; Year 4: 0.69, 0.53–0.90; Year 6: 0.85, 0.66–1.10).ConclusionsOur IV analysis indicated a potential causal effect of physical activity on reducing dementia risk that persisted for at least 4 years of follow-up. Thus, we conclude that physical activity should be recommended for older adults to reduce dementia risk.
Highlights
As of 2015, the World Health Organization estimated that approximately 50 million people had dementia worldwide; that number is expected to triple by 2050 asA meta-analysis of randomized controlled trials (RCTs) found no evidence that physical activity interventions reduced dementia risk [4]
A recent meta-analysis excluded individuals who experienced dementia onset within 10 years of follow-up and found no associations between physical inactivity and increased dementia risk [11]; the included studies measured physical activity only once and failed to consider the timevarying effects of physical activity at baseline. Another cohort study showed that the association between physical activity at baseline and dementia risk weakens over time [12]
We confirmed that the participant characteristics were well-balanced, with the exception of mean age, household income, and frequency of physical activity; residents in a non-snowy area were younger (73.7 vs. 74.4 years), had a higher household income (8.8% vs. 6.3% in the highest category), and engaged in physical activity more frequently (1.38 vs. 1.25 times per week)
Summary
As of 2015, the World Health Organization estimated that approximately 50 million people had dementia worldwide; that number is expected to triple by 2050 asA meta-analysis of randomized controlled trials (RCTs) found no evidence that physical activity interventions reduced dementia risk [4]. A recent meta-analysis excluded individuals who experienced dementia onset within 10 years of follow-up and found no associations between physical inactivity and increased dementia risk [11]; the included studies measured physical activity only once (more than 10 years ago) and failed to consider the timevarying effects of physical activity at baseline. Another cohort study showed that the association between physical activity at baseline and dementia risk weakens over time [12]. This study examined the potential causal effects of physical activity on reducing dementia risk using residency in a snowy area as an instrumental variable (IV) representing the physical activity of older adults
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
