Mentally Active Versus Passive Sedentary Behavior and Risk of Dementia: 19-Year Cohort Study

Sedentary behavior (sitting/reclining) has been associated with depression in adults, but the relationship with dementia remains unclear. To address this, associations of mentally passive (e.g., TV-viewing) and mentally active (e.g., office work) sedentary behaviors with incident dementia were examined, including how theoretically replacing mentally passive sedentary behavior with mentally active sedentary behavior, light and moderate-to-vigorous physical activity impacts incident dementia risk.

Data originate from the Swedish National March Cohort, including 20,811 adults aged 35-64 years (baseline, 1997). Incident dementia was identified through a linkage (2016) with the Swedish National Patient Register and the Swedish Cause of Death Register. Passive and mentally active sedentary behaviors as well as light and moderate-to-vigorous physical activity were also assessed using questionnaires. Analyses included single, partition, and substitution Cox proportional hazards models, adjusting for potential confounders. Analyses were conducted in 2025.

There were 569 incident cases of dementia over 393,104 person-years; median follow-up time was 19.2 years. Mentally passive sedentary behavior was associated with a higher incidence of dementia in crude (hazard ratio=1.16, 95% CI=1.11, 1.22) but not adjusted models (hazard ratio=1.04, 95% CI=0.98, 1.10). Each additional 1 hour per day of mentally active sedentary behavior was associated with a 4% lower risk for developing dementia (hazard ratio=0.96, 95% CI=0.93, 0.98). There was a significant age interaction, indicating a higher protective effect of mentally active sedentary behavior among older participants (aged 50-64 years). In the partition models accounting for all behaviors, increasing 1 hour per day of mentally active sedentary behavior, while maintaining passive sedentary behavior and light and moderate-to-vigorous physical activity constant, was associated with an 11% lower risk for incident dementia (hazard ratio=0.89, 95% CI=0.81, 0.97). Similarly, substituting 1 hour per day of passive sedentary behavior with the same amount of mentally active sedentary behavior was associated with a 7% reduction in the risk for incident dementia (hazard ratio=0.93, 95% CI=0.87, 0.99).

Mentally passive sedentary behavior may increase the risk of dementia. Replacing passive with mentally active sedentary behaviors or with physical activity may reduce the risk of dementia in older adults.