This updates an earlier review with 17 new studies, giving 74 studies and 4,227,297 participants, median age 67.3 years, followed for a median of ten years. The headline result is familiar: high physical activity was associated with a 20% lower risk of all-cause dementia, 21% lower for Alzheimer's disease and 29% lower for vascular dementia.
The new part is the split by domain. Leisure-time activity was associated with a 24% lower risk and household activity 15% lower. Occupational activity went the other way, associated with a 20% higher risk, and commuting activity 10% higher. Dose-response analyses were non-linear for both leisure and occupational activity.
The caveats are substantial and the authors state them. Certainty of evidence was very low to low, heterogeneity was extreme for the main estimates, and 93% of studies came from high-income countries. Occupational activity is entangled with education, income, air quality, injury and shift work, and no observational design separates those cleanly.
What it changes is the shape of the advice rather than its direction. The reflex response to a physically demanding job — that the patient already gets plenty of exercise — is not supported here. In Indian practice, where a large share of older adults have done manual work for decades and leisure exercise is often treated as a luxury, that distinction is the useful one: occupational exertion should not be counted as the protective kind.
- Ask what kind of activity a patient does, not only how much.
- Do not treat a physically demanding job as sufficient exercise for brain health.
- Recommend leisure activity specifically, with access in mind — a safe place and unhurried time are part of the prescription.
- Present this as one input to dementia risk, not as an established causal effect.
- Household activity counted as protective too, which matters for patients who cannot leave the house easily.
The statistics, in plain English
A relative risk of 0.80 means about 20% fewer dementia cases among the most active, and 1.20 for occupational activity means about 20% more. Two things should hold that in check. I-squared of 97.4% for the main estimate means the studies disagreed almost completely, so the pooled number is an average over results pointing in different directions. And the occupational finding rests on five studies against twenty for leisure, so it is much the weaker half. This is observational: people who take leisure exercise differ from those who do not in education, income and health, and adjustment never removes all of that. GRADE certainty of very low to low is the authors' own verdict on how much the estimates might move.
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