The study found that “mentally passive” sedentary behaviors (like watching TV) may increase dementia risk, but replacing these activities with activities that engage the brain (such as office work or knitting) could reduce the risk.
“This new finding is significant because we have identified what appears to be a novel risk factor for dementia,” says lead study investigator Mats Hallgren, PhD, a researcher at the Karolinska Institute in Stockholm.
The results suggest that if people replace passively sitting with mentally engaging activities (both sedentary or physically active), it could potentially reduce the number of adults who go on to develop dementia, Dr. Hallgren says.
Keeping the Brain Engaged While Sedentary Tied to Lower Dementia Risk
For the study, published in the American Journal of Preventive Medicine, researchers analyzed data from about 21,000 adults aged between the ages of 35 and 64 in the Swedish National March Cohort. Nearly 70 percent were women, and they were followed for nearly two decades.
Participants answered questionnaires about how they spent their days. They reported sedentary behaviors including watching TV, listening to music, and sitting in a bathtub. Mentally active sedentary activities included office work, reading a book, sitting in a meeting, knitting, and sewing.
Participants also reported their physical activity levels, including the weekly time spent walking, jogging, swimming, or hard training. Researchers determined dementia rates using the Swedish National Patient Register and Cause of Death Register.
The main findings include:
- Mentally passive sedentary behavior was associated with a higher incidence of dementia.
- Mentally active sedentary behavior was associated with a reduced risk of developing dementia.
- Each additional hour per day of mentally active sedentary behavior was associated with a 4 percent lower risk of developing dementia.
- Increasing active sedentary behavior by an hour per day — while maintaining levels of passive sedentary behavior and any physical activity — was tied to an 11 percent lower risk for dementia.
The results suggest that minimizing mentally passive sitting time, and replacing it with mentally or physically active tasks could reduce the risk of dementia in older adults, Hallgren says.
One limitation of the research is that questionnaires from 1997 didn’t capture activities we do while sitting today — things like social media use, video streaming, and smartphone scrolling, which previous research has suggested can impair focus.
Another is that the data is observational. Hallgren says his team is planning a new study to examine the real-world effects of replacing passive sitting with engaging mental or physical activities on dementia symptoms.
Why It’s Important to Distinguish Active Sitting From Passive Behaviors
“We often think of all sitting as harmful,” says Majid Fotuhi, MD, PhD, a neurologist in Washington, DC, and author of The Invincible Brain. Dr. Fotuhi was not involved with the study.
But this study shifts the conversation, he says, “from ‘avoid sitting’ to ‘engage your brain,’ which is far more meaningful for long-term brain health.” He suggests
“In other words, not all sitting is equal,” says Fotuhi, who wasn’t involved with the study. “Sitting can either weaken your brain or strengthen it, depending on how you use that time.”
Many activities typically done while sitting can strengthen the brain, like writing and creating art, potentially lowering your risk for dementia and Alzheimer’s disease, he adds.
“Activities that require a dynamic and engaged combination of attention, memory, language, or problem-solving may help maintain or strengthen neural circuits over time,” says Joel Salinas, MD, a behavioral neurologist and chief medical officer at Isaac Health in New York City.
Passive activities often “provide relatively little stimulation to those systems,” he says.
Is Scrolling on Your Phone a Mentally Active or Passive Activity?
The study didn’t specifically address which category scrolling falls in. But experts say it likely depends on how you’re using your phone.
Mindless, repetitive scrolling without reflection or interaction is likely a mentally passive activity, Dr. Salinas says. “It tends to involve low sustained attention and minimal cognitive effort.”
However, if you’re using your phone to “learn something new, read deeply, or engage thoughtfully,” it could become a mentally active activity, Fotuhi says.
“I suggest you set a timer to make sure you keep track of how long you scroll through your social media posts, and set a goal to learn five new things,” he adds.
The Brain Needs Physical Activity and Intellectual Engagement
Physical activity is essential to keep the brain and body healthy, Salinas adds. “Mentally engaging activities may confer additional benefit, but they do not offset the systemic effects of prolonged inactivity.”
The brain needs both movement and mental engagement, Fotuhi says. “They work together, not in competition.”
While some sitting is unavoidable, Hallgren recommends breaking up long periods of passive sitting with “something that you find mentally engaging or challenging.” And replace instances of mentally passive sitting with mentally active sitting when you can, Salinas says.
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