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. 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." The Alzheimer's Association says an 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 activity had 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.
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.
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