Summary: A 19-year longitudinal study has found that the type of sitting we do significantly impacts our risk of developing dementia. While sitting has long been viewed as a uniform health risk, researchers discovered a critical distinction: mentally passive sitting (like watching TV) increases dementia risk, whereas mentally active sitting (like reading or office work) appears to be protective.
The study suggests that even if we can’t reduce our total sitting time, “swapping” passive habits for cognitively engaging ones could significantly lower the risk of cognitive decline in later life.
Key Facts
- The Cognitive Divider: The study differentiates sedentary behavior by brain activity level rather than just energy expenditure.
- Protective Substitution: Replacing passive sitting with mentally active behaviors was associated with a significant reduction in dementia onset.
- Massive Dataset: Researchers followed 20,811 adults across 3,600 Swedish cities and villages over nearly two decades (1997–2016).
- Independent of Exercise: The protective effect of mentally active sitting remained significant even when accounting for levels of light, moderate, and vigorous physical activity.
Source: Elsevier
New research distinguishing between passive and mentally active sitting in association with dementia has found that adults who engaged in extended durations of mentally passive sedentary behaviors had a higher risk of dementia.
Replacing passive with mentally active sedentary behaviors was shown to reduce the risk of dementia onset in later life.
The study in the American Journal of Preventive Medicine, published by Elsevier, has the potential to inform public health guidelines and preventive strategies to reduce dementia.
Globally, populations are aging. Dementia is the third highest cause of mortality and the seventh largest cause of disability among older adults globally. It is a prevalent age-related condition affecting many adults’ quality of life, including their families and carers. Prevention is important, and a key part of this involves identifying modifiable risk factors.
It was previously thought that all sedentary behaviors were associated with a higher risk of developing dementia. However, in recent studies, researchers found that mentally passive sedentary behaviors (such as watching TV) increased the risk of depression, while mentally active sedentary behaviors (such as reading and office work) appeared to be protective.
Most adults spend about 9-10 hours per day sitting. Previous research has shown that extended, uninterrupted sitting is a risk factor for cardiovascular disease, type 2 diabetes, and depression. It has also been associated with dementia.
This is the first study to distinguish between passive and mentally active sitting in association with dementia.
Lead investigator Mats Hallgren, PhD, Department of Public Health Sciences, Karolinska Institute, Sweden, and Baker-Deakin Department of Lifestyle and Diabetes, Institute for Physical Activity and Nutrition (IPAN), Deakin University, Australia, notes, “While all sitting involves minimal energy expenditure, it may be differentiated by the level of brain activity. How we use our brains while we are sitting appears to be a crucial determinant of future cognitive functioning and, as we have shown, may predict dementia onset.”
Researchers analyzed data from a longitudinal study of 20,811 adults aged 35-64 years followed over 19 years (1997-2016). The baseline survey included questions about sedentary behaviors, physical activity, and other behaviors associated with dementia. Incident dementia was identified by linking the data of the 1997 survey with the Swedish National Patient Register and the Swedish Cause of Death Register.
Utilizing various statistical models, investigators examined the associations with dementia of (statistically) substituting passive with mentally active sedentary behaviors. “The prospective study design allowed us to establish the direction of these relationships and infers but does not establish causality. Controlled trials are needed to confirm these important observational study findings,” notes Dr. Hallgren.
The study’s main findings are as follows:
- Mentally active sedentary behavior was associated with a reduced risk of developing dementia among middle-aged and older adults.
- Increasing time spent in mentally active sedentary behavior was associated with a significant reduction in dementia risk while maintaining the levels of passive sedentary behavior, light and moderate-to-vigorous physical activity.
- Replacing the amount of time spent in mentally passive sedentary behavior for equivalent durations of mentally active sedentary behavior was also associated with a reduction in the risk for developing dementia.
Given the extensive survey method used to collect these data (3,600 cities and villages across Sweden), the investigators believe the findings are likely generalizable to a wider global population.
Dr. Hallgren concludes, “Sedentary behavior is a ubiquitous but modifiable risk factor for many health conditions, including dementia. Our study adds the observation that not all sedentary behaviors are equivalent; some may increase the risk of dementia, while others may be protective. It is important to remain physically active as we age, but also mentally active—especially when we are sitting.”
Key Questions Answered:
A: Not exactly. Physical activity is still vital for your heart and metabolism. However, this study shows that if you are going to sit for 9–10 hours a day (as most adults do), choosing a book or a challenging task over the TV remote could be a “brain-saver” that lowers your dementia risk.
A: It’s about the “mental load.” TV usually requires very little cognitive processing. Office work, puzzles, or reading require your brain to constantly decode information, solve problems, and stay alert. This mental “exercise” helps maintain the neural connections that ward off dementia.
A: Surprisingly, yes. The study found that even in people who were physically active, the type of sitting they did still influenced their dementia risk. Exercise is great, but it doesn’t completely “cancel out” the effects of how you use your brain during sedentary hours.
Editorial Notes:
- This article was edited by a Neuroscience News editor.
- Journal paper reviewed in full.
- Additional context added by our staff.
About this dementia research news
Author: Astrid Engelen
Source: Elsevier
Contact: Astrid Engelen – Elsevier
Image: The image is credited to Neuroscience News
Original Research: Open access.
“Mentally Active Versus Passive Sedentary Behavior and Risk of Dementia: 19-Year Cohort Study” by André O. Werneck, Michael J. Wheeler, David W. Dunstan, Neville Owen, Ylva Trolle Lagerros, and Mats Hallgren. American Journal of Preventive Medicine
DOI:10.1016/j.amepre.2026.108317
Abstract
Mentally Active Versus Passive Sedentary Behavior and Risk of Dementia: 19-Year Cohort Study
Introduction
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.
Methods
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.
Results
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).
Conclusions
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.
