ByLucy Notarantonio
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For years, scientists have known that regular physical activity can help lower the risk of dementia. But a new study suggests that where and how people get that activity may matter just as much as how much they do
A meta-analysis involving more than 4.2 million people found that leisure-time exercise, including activities such as walking, cycling, running, swimming and sports, 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 developing the condition
Natan Feter, the study’s first author, told Newsweek: “Occupational physical activity often involves spending time in environments that may be less favorable to health, including greater exposure to air pollution and psychosocial stressors.”
The findings, published in The Lancet Public Health, are the first to systematically investigate whether the “physical activity paradox” applies to dementia
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The paradox, already documented in cardiovascular research, refers to the observation that physically demanding jobs do not appear to provide the same health benefits as voluntary exercise and may even be associated with poorer health outcomes
Feter said: “The observed associations may therefore partly reflect the cumulative effects of social, economic, and environmental adversities rather than being fully attributable to occupational physical activity per se
“This dimension of risk should be interpreted through a structural lens, recognizing these exposures as sociocultural and environmental drivers of health rather than as biological traits.”
Leisure-Time Exercise Linked to Lower Dementia Risk
The Alzheimer’s Association saysan estimated 7.4 million Americans are living with Alzheimer’s dementia
The research team, led by David Raichlen, professor of biological sciences and anthropology at the USC Dornsife College of Letters, Arts and Sciences, analyzed data from 74 cohort and case-control studies involving more than 4.2 million participants aged between 45 and 93 across 30 countries
Participants were followed for a median of 10 years, during which researchers tracked diagnoses of all-cause dementia, Alzheimer’s disease and vascular dementia
Overall, people who engaged in higher levels of leisure-time physical activityhad a 24 percent lower risk of dementia compared with those who were least active. Household physical activity also appeared beneficial, although that finding was based on a single study
By contrast, occupational physical activity was associated with a 20 percent higher risk of dementia. Active commuting was also linked to a modest increase in risk, though those findings were drawn from only two studies.
“The findings challenge the long-held assumption that ‘every move counts’ for brain health,” said Feter, a postdoctoral fellow in Raichlen’s Evolutionary Biology of Physical Activity Lab, in a statement
Work Versus Play
The researchers noted that physical activity is often treated as a single category, despite including a wide range of activities such as exercise, manual labor, commuting and housework
According to the authors, these different forms of movement take place in very different circumstances and may affect long-term health in distinct ways
Feter told Newsweek: “Occupational physical activity 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.”
Whereas leisure-time activity is more likely to be self-selected, varied, and socially engaging
“However, a single factor is unlikely to explain this association,” Feter said. “The social and commercial determinants of physical activity are complex and multifaceted, and understanding why some individuals have more opportunities to engage in safe and meaningful physical activity than others warrants further investigation.”
Manual occupations are more likely to involve psychosocial stress, lower job control, hazardous working conditions and greater exposure to air and noise pollution, factors that have each been independently linked to dementia risk
Workers in these roles may also have fewer opportunities for recreational exercise because of fatigue, time constraints or limited access to safe places for physical activity
The study also found contrasting patterns between leisure-time and occupational activity. Higher levels of leisure-time exercise were associated with progressively lower dementia risk until the benefits leveled off. By comparison, higher amounts of occupational physical activity were associated with progressively greater dementia risk before that association also plateaued
Researchers Call for Further Investigation
The authors cautioned that evidence remains limited for both household activity and active commuting, making it difficult to draw firm conclusions about those areas
Most of the studies included in the analysis were conducted in high-income countries, despite low- and middle-income countries being expected to experience the largest increases in dementia cases in the coming decades
Another limitation is that nearly all of the studies relied on self-reported physical activity, which can introduce recall bias
However, Feter said the consistency of the findings across multiple sensitivity analyses suggests the association warrants attention
Researchers stressed that the results do not mean people should avoid physically active jobs. Because the review was based on observational studies, it cannot prove that occupational activity causes dementia
Instead, the findings highlight the importance of considering the context in which physical activity takes place. Leisure-time activity remained protective, while occupational activity remained associated with elevated dementia risk, even after accounting for factors including age, education and chronic disease
The authors also pointed to research published last month in Alzheimer’s & Dementia by Raichlen, Feter and colleagues. That study found that mentally active sedentary behaviors, such as desk-based work, were associated with greater volume in regions of the brain’s cortex involved in executive function when compared with passive sedentary activities like watching television
The researchers said the findings have implications for public health messaging and dementia prevention strategies
Rather than focusing solely on encouraging people to move more, they said future efforts may need to consider the conditions under which physical activity occurs
“In other words, when it comes to protecting the brain, the context of physical activity may matter just as much as movement itself,” Raichlen 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.”
Reference
Raichlen, D.A., Feter, N. et al. (2026) ‘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: Marc Vargas andJames Debens
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