STOCKHOLM — Researchers at the Karolinska Institute in Stockholm found that mentally active sedentary behaviors reduced dementia risk in a 19-year study of Swedish adults. The study tracked 20,811 participants who reported their physical activity levels and time spent in different types of sedentary behavior.

Scientists surveyed participants, mostly women aged 35 to 64, about their weekly physical activity and daily time spent in mentally active and mentally passive sedentary behavior. The study first surveyed participants in 1997 and followed them up 19 years later to assess their dementia risk and status.

Mentally active sedentary behaviors in the study included office work, sitting in meetings, knitting and sewing. Using a computer to solve puzzles was classified as mentally active sedentary behavior in the study. Watching television or listening to music while sedentary was classified as mentally passive behavior in the study.

Participants with higher amounts of mentally passive sedentary behavior had a higher risk of developing dementia in the future. Adding one hour of mentally active sedentary behavior was estimated to decrease dementia risk by 4%. Replacing one hour of mentally passive sedentary behavior with mentally active sedentary behavior was estimated to decrease dementia risk by 7%.

Combining physical activity such as walking with mentally active sedentary behavior was estimated to decrease dementia risk by 11%. "The brain works like a muscle," said Mats Hallgren, Principal Researcher at the Karolinska Institute.

The initial questionnaire for the study was conducted before smartphones, social media and endless scrolling existed. Professor Adam Brickman said that passive viewing of non-stimulating content is more common today than it was in 1997.

"The next time you have a serious task or you need to concentrate, you're less capable because your brain networks have been hijacked by this passive reception," said Hussein Yassine, Professor of Neurology at the University of Southern California Keck School of Medicine. Because the study relied on self-reported data, it cannot establish whether mentally passive activities increase dementia risk or whether individuals at higher risk are more likely to engage in such activities.

Sedentary behavior, defined as long periods of sitting, lying down or reclining, is linked to major risk factors for dementia such as high blood pressure, heart disease, diabetes and obesity. Extended periods without mentally engaging the brain can negatively affect parts of the brain associated with memory and learning.