A meta-analysis of over 4.2 million people across 30 countries suggests that the type of physical activity performed may influence dementia risk.

Researchers from the University of Southern California (USC) found that leisure-time exercise, such as walking, running, swimming and cycling, was associated with a 24 per cent lower risk of dementia compared to the least active participants. Conversely, physical activity performed as part of a job was linked to a 20 per cent higher risk of the condition.

The study, published in The Lancet Public Health, examined 74 cohort and case-control studies involving participants aged 45 to 93. Researchers tracked diagnoses of all-cause dementia, Alzheimer's disease and vascular dementia over a median period of 10 years.

Natan Feter, a postdoctoral fellow at USC and the study's first author, noted that strenuous activity at work affects risk differently than leisure exercise. He suggested work-related activity often involves repetitive, low-complexity tasks and may occur in environments with hazardous exposures like air and noise pollution.

"The findings challenge the long-held assumption that 'every move counts' for brain health,"

The authors stated that the findings should not be interpreted as evidence that physically active jobs cause dementia, noting the observational nature of the study cannot prove cause and effect. The researchers also acknowledged limitations, including the fact that most studies came from high-income countries and relied on self-reported activity levels.

Lead researcher David Raichlen, a professor at USC, said that improving access to recreational facilities and reducing harmful workplace exposures may be as important as promoting physical activity itself.