A meta-analysis of 69 studies involving nearly 4.5 million participants suggests that sleeping between seven and eight hours per night is associated with the lowest risk of developing dementia. The findings are published in PLOS One.
Researchers at York University in Canada analysed pooled data to examine associations between dementia risk and three modifiable factors: physical activity, sedentary time, and sleep duration.
The analysis found that sleeping fewer than seven hours per night was associated with an 18% increase in dementia risk, whilst sleeping more than eight hours was linked to a 28% increase. Prolonged sitting (more than eight hours daily) and insufficient physical activity (fewer than 150 minutes weekly) were also associated with elevated dementia risk.
The researchers suggest that regular physical activity, reduced sedentary time, and appropriate sleep duration may promote vascular, neurotrophic, and anti-inflammatory effects that collectively support brain health and could delay the onset or progression of dementia.
Importantly, the study highlights associations rather than causal relationships. The relationship between sleep and dementia is complex: excessive sleep may be an early indicator that neurodegeneration has already begun rather than a direct driver of disease.
The review included data from participants as young as 35, younger than many dementia studies, and all studies followed participants from a dementia-free baseline. However, limitations include variability in data collection methods across studies, and limited data on sedentary behaviour specifically.
With dementia cases projected to rise and estimates suggesting that approximately half of cases could be prevented by addressing lifestyle factors, these findings add to the evidence supporting modifiable behaviours for brain health.
Source: Oye-Somefun A et al. PLOS One (2026).
