1. This large, prospective cohort study from Japan demonstrated an inverse association between the risk of disabling dementia and daily total physical activity, total moderate to vigorous physical activity (MVPA), and leisure-time MVPA.
2. After exclusion of participants diagnosed within the first ten years of the study, the majority of inverse associations were lost, except for leisure-time MVPA in men with the risk of disabling dementia, which remained significant.
Evidence Rating Level: 2 (Good)
Study Rundown: The evidence regarding whether physical activity plays a role in preventing dementia is mixed. Some studies demonstrate an inverse relationship between physical activity and the incidence of dementia; however, there is a caution that these associations are prone to reverse causation bias. This long-term, large, prospective cohort study investigated whether daily physical activity is inversely associated with the risk of developing dementia, including analyzing whether reverse causation bias may be at play. The primary exposures were daily total physical activity, total moderate to vigorous physical activity (MVPA), and leisure-time MVPA measured in metabolic equivalents (METs). Participants were divided into four equally sized quartiles based on total daily activity (METs). Compared to the first quartile, higher daily total physical activity, total MVPA, and leisure-time MVPA were inversely associated with the risk of dementia in both men and women. This study evaluated whether the risk of disabling dementia remained significantly different between the highest and lowest quartiles after excluding participants diagnosed in the first few years of the study to assess for reverse causation bias. By excluding male patients diagnosed within the first seven years and female patients diagnosed within the first eight years, the associations of daily total physical activity and total MVPA with disabling dementia incidence were lost. Conversely, even after excluding diagnoses within the first ten years, leisure time MVPA remained significantly inversely associated with the incidence of disabling dementia in men but not in women. Overall, this study demonstrated that higher physical activity was inversely associated with the risk of disabling dementia; yet this association may be attributed to reverse causation bias since they disappeared after the exclusion of diagnoses within the first ten years of the study. However, higher leisure-time MVPA in men may reduce the risk of disabling dementia. However, one limitation of this study is that it did not classify dementia types that patients were diagnosed with; perhaps physical activity may reduce the risk of certain dementia subtypes and not others.
Click to read the study in JAMA Network Open
Relevant Reading: Physical activity and risk of cognitive impairment and dementia in elderly persons
In-Depth [prospective cohort]: This study included 43 896 participants (mean age, 61.0 years; 53.9% women) from 8 public health centres in Japan. Surveys were first collected between 2000 and 2003, with follow-ups between 2006 and 2016. Follow-up surveys were completed 5 and 10 years after the baseline survey. The main exposures were daily total physical activity, total MVPA, and leisure-time MVPA. The primary outcome was the incidence of disabling dementia. The cohort was divided into four, equally sized quartiles based on daily total METs (median [range]: Q1, 29.6 [22.4-32.1]; Q2, 34.5 [32.1-37.5]; Q3, 42.5 [37.6-49.0]; Q4, 59.7 [49.0-92.5]). The risk of dementia significantly decreased with increased daily total physical activity compared to Q1 in both men (Q2: aHR, 0.73 [95% CI, 0.65-0.82]; Q3: aHR, 0.69 [95% CI, 0.61-0.78]; Q4: 0.75 [95% CI, 0.66-0.85]) and women (Q2: aHR, 0.76 [95% CI, 0.69-0.84]; Q3: aHR, 0.73 [95% CI, 0.66-0.81]; Q4: 0.75 [95% CI, 0.67-0.84]). Upon exclusion of participants diagnosed within the first nine years post-baseline survey, the association between total physical activity and dementia risk disappeared in men (Q4 vs. Q1: aHR, 0.99 [95% CI, 0.76-1.29]) and women (Q4 vs. Q1: aHR, 0.93 [95% CI, 0.74-1.17]). Similar findings were observed for total MVPA. In contrast, the inverse association between leisure-time MVPA and disabling dementia remained significant in men (Q4 vs. Q1: aHR, 0.72 [95% CI, 0.56-0.92]) but not in women (Q4 vs. Q1: aHR, 0.91 [95% CI, 0.75-1.12]) after nine years.
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