ByMaria Azzurra Volpe
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A major new analysis suggests that, when it comes to dementia risk, how people are physically active may matter as much as how much they move
Researchers from the University of Southern California (USC) found that leisure-time exercise, including activities such as walking, running, swimming and cycling, was associated with a significantly lower risk of dementia. In contrast, physical activity performed as part of a person’s job was linked to a higher risk of the condition
The findings come from a meta-analysis published in The Lancet Public Healththat examined data from 74 cohort and case-control studies involving more than 4.2 million people across 30 countries
For years, studies have pointed to regular physical activity as a potential way to help reduce dementia risk. However, the new research suggests that lumping all forms of movement together may overlook important differences between recreational exercise and workplace physical activity
The researchers investigated whether a phenomenon known as the “physical activity paradox” might also apply to dementia. The paradox, already documented in cardiovascular research, refers to the observation that physically demanding occupations do not appear to provide the same health benefits as voluntary exercise and may even be associated with worse outcomes
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Participants were between 45 and 93 years old and were followed for a median of 10 years. During that period, researchers tracked diagnoses of all-cause dementia, Alzheimer’s disease and vascular dementia
The analysis found that people who engaged in higher levels of leisure-time physical activity had a 24 percent lower risk of dementia compared with those who were the least active
Meanwhile, occupational physical activity was associated with a 20 percent higher dementia risk
The study also found signs that household physical activity could be beneficial, although the evidence came from only one study. Active commuting, such as walking or cycling for transportation, was associated with a modest increase in risk, but those findings were based on just two studies
“The findings challenge the long-held assumption that ‘every move counts’ for brain health,” said Natan Feter, the study’s first author and a postdoctoral fellow in USC’s Evolutionary Biology of Physical Activity Lab
Feter told Newsweek that strenuous physical activity at work affects dementia risk differently than leisure exercise because it often involves repetitive, low-complexity tasks that may limit the accumulation of cognitive reserve
“It may also occur in environments characterized by hazardous exposures, such as air and noise pollution. In contrast, leisure-time activity is more likely to be self-selected, varied, and socially engaging,” he said
The authors argue that movement itself is unlikely to explain the higher dementia risk associated with occupational physical activity. Instead, they suggest the relationship may reflect broader social and environmental factors that often accompany physically demanding work
Professor Arshad Rather, a consultant geriatrician and general physician at Medical Express Clinic, told Newsweek that voluntary exercise helps the brain with better blood flow and blood pressure control, lower inflammation, and better glucose handling, and all of that protects the small vessels that feed the brain
“Then there is the social side: a walk with a friend, a tennis game, a swim club. Loneliness and isolation by themselves are dementia risks. Voluntary exercise often comes with company, daylight, fresh air and something to look forward to. All of these combined are beneficial to a good quality of life, which is ultimately what it’s all about,” Rather said
“There is also cognitive engagement. Sport involves planning, reaction, coordination. Even a brisk walk in a new place asks the brain to navigate new experiences. Repetitive lifting on a production line does not do the same job
“Finally, you are more likely to sleep and eat better when exercise is something you enjoy rather than something that has already drained you,” he said
According to Rather, physically demanding jobs often come with chronic stress, shift work, noise, air pollution, fluorescent lights, less control over pace and hours, and not enough recovery time
“We’ve all heard the stories of factory workers that barely get enough time off to go to the toilet,” he said
Moreover, workers in physically demanding jobs may also have fewer opportunities to participate in recreational exercise because of fatigue, time constraints or limited access to safe exercise spaces
The analysis found contrasting patterns between leisure and work-related activity. Dementia risk continued to decrease as leisure-time exercise increased before eventually plateauing. Occupational physical activity showed the opposite trend, with higher levels associated with progressively greater risk until that relationship also leveled off
Feter said: “In the paper, we call for shifting focus away from individual-level behavioral changes and toward structural determinants, prioritizing worker-centered policies and equitable urban planning that expand access to meaningful leisure-time physical activity.”
The authors stressed that the findings should not be interpreted as evidence that physically active jobs cause dementia
Because the study is observational, it can identify associations but not prove cause and effect
The researchers also acknowledged several limitations. Evidence on housework and active commuting remains limited; most available studies came from high-income countries, and nearly all relied on participants reporting their own physical activity levels, which can introduce recall bias
Even so, the relationship remained consistent across multiple sensitivity analyses, giving researchers confidence that the findings warrant further attention
The study’s authors say the results have important implications for public health efforts to reduce dementia risk
“In other words, when it comes to protecting the brain, the context of physical activity may matter just as much as movement itself,” David Raichlen, a professor of biological sciences and anthropology at USC and the study’s lead researcher, said. “Improving access to safe parks, walking trails and recreational facilities, ensuring people have adequate leisure time for exercise, and reducing harmful workplace exposures may ultimately prove as important as promoting physical activity itself.”
According to Feter, the most important next step in the research would be to further examine not only how often, but also when and why, people engage in physical activity and sedentary behavior. Investigate how this domain-specific association manifests within particular occupational groups and assess the long-term effects of occupational exposure to physical activity, sedentary behavior, and other work-related characteristics on brain health
Reference:
Raichlen et al. Domain-specific physical activity and the risk of dementia: a systematic review and meta-analysis with 4 million participants. The Lancet Public Health
Contact Newsweek editors on this story: Sirena Bergman and Sam Wilson
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