Jobs that require strenuous physical activity, heavy lifting, or prolonged standing may increase the risk of developing dementia by as much as 20%, according to a major study published in The Lancet Public Health. This finding challenges the long-held assumption that all physical activity is beneficial for brain health.
The research, which analyzed data from over 4.2 million participants aged 45 to 93, found that individuals who engaged in higher levels of leisure-time physical activity—such as running, swimming, or cycling—had a 24% lower risk of dementia compared to those who were least active. Dementia includes conditions like Alzheimer's disease and vascular dementia.
Scientists from the University of Southern California observed that while exercise in leisure time appears protective, physical activity performed as part of a job was associated with an increased risk. The study also noted a potential, though uncertain, modest increase in dementia risk among those who actively commuted to work.
Dementia is a significant cause of disability, with physical inactivity identified as one of 14 modifiable risk factors that contribute to 45% of cases. This new research suggests that the context in which physical activity occurs is crucial.
Leisure-time exercise is typically self-directed, often social, and may involve stress reduction. In contrast, physically demanding jobs can involve repetitive tasks, heavy lifting, limited recovery periods, and exposure to workplace hazards. Researchers indicated that the increased risk from occupational physical activity is unlikely due to the movement itself, but rather due to associated factors.
These factors may include psychosocial stress, exposure to air and noise pollution, longer or unsociable working hours, and fewer opportunities for recreational exercise, all of which have been independently linked to dementia risk. The findings suggest that improving access to safe recreational facilities, ensuring adequate leisure time for exercise, and reducing harmful workplace exposures could be as important for brain health as promoting general physical activity.
This research follows previous findings, including a study from York University in Canada, which indicated that sitting for more than eight hours a day could increase dementia risk by 27%. That study also highlighted the protective effects of regular exercise and sufficient sleep.
Another recent study, published in Alzheimer’s & Dementia, found that sedentary but mentally stimulating behaviors, like desk work, were associated with higher brain cortex volume compared to passive sedentary activities such as watching television. The collective research underscores the importance of considering the context and nature of physical activity when developing public health strategies for dementia prevention.