Engagement means activities such as knitting or solving a puzzle, instead of mindlessly scrolling or passively watching a screen.
Scientists at the Karolinska Institute in Stockholm surveyed 20,811 Swedish adults, mostly women between the ages of 35 and 64, about their weekly physical activity and how much daily time they spent in “mentally active” and “mentally passive” sedentary behavior. They first questioned the participants in 1997 and followed up 19 years later to assess dementia risk and status.
Sedentary behavior — long periods of sitting, lying down or reclining — is linked to “major risk factors for dementia,” like high blood pressure, heart disease, diabetes and obesity, said Mats Hallgren, a principal researcher at the Karolinska Institute and an author of the study.
However, brain activity is a crucial element in protecting against that damage.
The brain “works like a muscle,” he said. Not actively using it for extended periods of time can eventually negatively affect the parts linked to memory and learning.
In the questionnaire, being mentally active while sedentary included office work, sitting in a meeting, as well as knitting and sewing. Activities like using a computer to solve a puzzle were considered intellectually stimulating.
Watching TV or listening to music while sedentary counted as mentally passive.
In the study, which was published Thursday in the American Journal of Preventive Medicine, participants who engaged in more mentally passive sitting had a “significantly higher risk of developing some type of dementia in the future,” Hallgren said.
Concerns about ‘brain rot’ behavior
Using a statistical model, researchers then predicted how changes in mental activity would affect dementia risk.
They calculated that adding an hour of mentally active behavior while sedentary decreased dementia risk by 4%; replacing an hour of mentally passive behavior with mentally active behavior decreased the risk by 7%; and combining physical activity, like walking, with active mental behavior decreased the risk by 11%.
The study has limitations. Because the initial questionnaire was almost three decades ago, smartphones, social media and endless scrolling didn’t exist. An earlier review suggested that older adults reaped cognitive benefits from phone usage, but less is known about children and young adults. And because it’s based on self-reporting, the research can’t conclude whether mentally passive activities increase the risk of dementia, or whether people with a greater dementia risk may engage in passive activities more.
Dr. Hussein Yassine, a professor of neurology at the University of Southern California Keck School of Medicine, speculates that phone and social media usage may pose a similar risk by affecting our ability to concentrate.
“It’s going to be affecting your ability to process information and potentially build synapses in certain areas in the brain that help with concentrating,” Yassine said. “So 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.”
Adam Brickman, a professor of neuropsychology at Columbia University, said that the rise of short-form content like TikTok has exponentially increased mentally passive behavior.
“If you think about how kids, even adults, are spending their time passively looking at content that I think none of us would classify as stimulating or active behavior, it’s certainly a lot higher today than it was in 1997,” said Brickman, who was not associated with the new study.
Recent research has raised worries about cognitive deterioration, popularly called “brain rot,” including shorter attention spans that may accompany heavy consumption of short-form video.
“This sort of nonstop-without-thinking scrolling from one YouTube video to the next, those sorts of behaviors when you’re sitting for a very long time, if they’re repeated over time, are likely to be associated with depression and anxiety and stress-related conditions, compared to more active engagements and doing work-type scrolling,” he said.
Even if technology has changed, “the pathways that affect dementia fundamentally are the same in people today that they were 30 years ago,” Hallgren said.
His advice for lowering dementia risk is simple: “Sit less and move more, more often.”
