Most Physical Activity Is Tied to Lower Dementia Risk, but This Type May Raise It

A new study of over 4.2 million individuals suggests that the type of physical activity may impact dementia risk differently than previously thought. Researchers found that higher levels of physical activity, such as walking, running, swimming, cycling, or sports, were tied to a 20% lower risk of all-cause dementia over a 10-year period compared to the lowest level of activity.

Similarly, leisure-time activities like these were also associated with reduced dementia risk (RR 0.76, 95% CI 0.65-0.88). Household activities showed some benefit as well but were based on a single study.

However, the study also revealed that job-related physical activity appeared to increase dementia risk (RR 1.20, 95% CI 1.01-1.42). Active commuting was also linked to higher dementia risk based on two studies. The findings challenge the common belief that any physical movement is beneficial for brain health. The study's lead author, Natan Feter from the University of Southern California, noted that this is the first systematic examination of whether the "physical activity paradox" (physically demanding jobs offering fewer health benefits than voluntary exercise) applies to dementia.

Experts point out that occupational physical activity is often closely linked to factors like higher stress levels, hazardous environmental exposures, and lower educational attainment, which are known risk factors for dementia. Recreational movement, on the other hand, might provide cognitive benefits through social interaction and cognitive engagement, especially in team and partner sports. These activities could also reduce social isolation, which is a risk factor for cognitive decline.

The study analyzed 74 cohort and case-control studies, encompassing 4.23 million people with a median age of 67.3 years. Most participants were women (52.8%). The majority of studies were conducted in high-income countries. Researchers found that high physical activity levels were associated with reduced risks of Alzheimer's disease (HR 0.79, 95% CI 0.70-0.90) and vascular dementia (HR 0.71, 95% CI 0.58-0.87) compared to the lowest level of activity over a median follow-up of 10 years.

Limitations include reliance on self-reported physical activity data and potential reverse causation, which could have overestimated the protective effects of leisure-time physical activity on dementia risk.