Swapping TV time for reading or office work could lower dementia risk, a 19-year study suggests.
The finding comes from what is described as the first study to distinguish between mentally passive and mentally active sitting in relation to dementia.
Most adults spend about nine to 10 hours a day sitting, and earlier research has linked prolonged, uninterrupted sitting to cardiovascular disease, type 2 diabetes, depression and dementia.
The new research suggests not all sitting carries the same risk.
Mentally passive activities such as watching TV have been linked to a higher risk of depression, while mentally active sedentary behaviours such as reading and office work appeared to be protective.
Lead investigator Dr Mats Hallgren said: “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.”
The study, led by researchers at the Karolinska Institute in Sweden and Deakin University in Australia, analysed data from 20,811 adults aged 35 to 64 who were followed over 19 years.
Researchers examined what happened when time spent in passive sitting was statistically replaced with mentally active sitting.
The results showed that mentally active sedentary behaviour, meaning activities done while sitting with little physical movement, was associated with a reduced risk of developing dementia.
Spending more time in mentally active sedentary behaviour was linked to a significant reduction in dementia risk while maintaining levels of passive sedentary behaviour and physical activity. Replacing passive sitting with equivalent amounts of mentally stimulating activity was also associated with a lower risk of developing the condition.
Dementia, which affects memory, thinking and everyday functioning, is the third highest cause of death and the seventh largest cause of disability among older adults globally.
Hallgren said: “Sedentary behaviour is a ubiquitous but modifiable risk factor for many health conditions, including dementia.
“Our study adds the observation that not all sedentary behaviours 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.”
The researchers said the prospective study design allowed them to establish the direction of the relationships, but it does not prove cause and effect.
Controlled trials would be needed to confirm the findings.
However, given the extensive survey method used, covering 3,600 cities and villages across Sweden, they said the findings are likely to be generalisable to a wider global population.
