New USC research suggests that it’s not just the amount of physical activity but also the context of that activity — whether it’s for work or leisure — that makes a difference in lowering the risk of dementia, the school announced Wednesday.
A meta-analysis of more than 4.2 million people found that leisure exercise such as walking, cycling, running, swimming or playing sports is associated with a substantially lower risk of dementia, while activity performed as part of a job appears to be linked with a higher risk of developing the condition.
The findings, published in The Lancet Public Health, are the first to systematically examine whether the so-called “physical activity paradox” extends to dementia. The paradox, well documented in cardiovascular research, describes the surprising observation that physically demanding jobs do not provide the same health benefits as voluntary exercise, and may even increase disease risk.
“The findings challenge the long-held assumption that `every move counts’ for brain health,” said Natan Feter, the study’s first author, postdoctoral fellow in Raichlen’s Evolutionary Biology of Physical Activity Lab at USC and researcher in the Graduate Program of Epidemiology at Universidade Federal do Rio Grande do Sul in Brazil.
The research team was led by David Raichlen, professor of biological sciences and anthropology at the USC Dornsife College of Letters, Arts and Sciences. They analyzed data from 74 cohort and case-control studies involving more than 4.2 million participants aged 45 to 93 years across 30 countries. Participants were followed for a median of 10 years, during which investigators tracked diagnoses of all-cause dementia, Alzheimer’s disease and vascular dementia.
Overall, people who engaged in higher levels of leisure-time physical activity had a 24% lower risk of dementia than those who were least active. Household physical activity also appeared beneficial, although evidence came from only a single study. By contrast, occupational physical activity was associated with a 20% higher dementia risk, while active commuting showed a modest increase in risk, though those findings were based on just two studies.
The researchers say leisure-time exercise is typically self-directed, can be performed at an enjoyable intensity and is often accompanied by social interaction or stress reduction. Physically demanding jobs, on the other hand, may involve repetitive tasks, prolonged standing, heavy lifting, limited recovery time and exposure to workplace hazards.
The authors argue that the apparent harms associated with occupational activity are unlikely to be caused by movement itself. Instead, they may reflect the broader social and environmental conditions that often accompany physically demanding work.
“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,” Raichlen said.
The study can be found at thelancet.com/journals/lanpub/article/PIIS2468-2667(26)00142-8/fulltext.