How we engage our brains while sitting for long periods may affect cognitive health later in life. A new study from Karolinska Institutet, published in the American Journal of Preventive Medicine, shows that adults who spend most of their sedentary time on mentally passive activities, such as watching TV, face a higher risk of developing dementia. By contrast, brain-stimulating sedentary activities, such as reading, appear to reduce the risk.
Sedentary behaviour is widespread, with most adults sitting for around nine to ten hours a day. Previous research has linked prolonged sitting to cardiovascular disease, diabetes and depression. While its potential impact on the development of dementia has also been recognised, the new study is the first to distinguish between passive and mentally active sedentary behaviour.
The researchers analysed data from 20,811 individuals aged 35-64 who were followed over a period of 19 years. By linking questionnaire responses from 1997 with Swedish patient and cause-of-death registers, they were able to examine how sedentary habits are associated with later diagnoses of dementia. The analysis accounted for a range of factors, including physical activity and lifestyle habits. The researchers also used so-called isotemporal substitution modelling to statistically examine what happens when passive sitting is replaced with mentally active sedentary behaviors.
Mental activity supports brain health
"We found that longer periods of mentally passive sedentary behaviour were associated with a higher risk of dementia,' says Mats Hallgren , senior researcher at the Department of Global Public Heal th and lead author of the study. 'When passive sitting was instead replaced with mentally active activities, the risk decreased."
The study cannot establish causality, but the long follow-up period makes it possible to observe how early habits are associated with health later in life.
"Sedentary behaviour is common, but fortunately, it can also be modified. Our study shows that not all sitting is the same - how we use our brains while sitting may be an important factor for future cognitive and mental health," says Mats Hallgren.
The researchers hope that the findings will contribute to future guidelines on how both physical and mental activity can support brain health as we age.
Publication
Mentally Active Versus Passive Sedentary Behavior and Risk of Dementia: 19-Year Cohort Study André O. Werneck, Michael J. Wheeler, David W. Dunstan, Neville Owen, Ylva Trolle Lagerros, Mats Hallgren, American Journal of Preventive Medicine, 2026, doi.org/10.1016/j.amepre.2026.108317
