Published on: Feb 12, 2026
Researchers at Monash University examined data from nearly 90,000 participants to identify the most beneficial balance between sleep and physical activity for lowering dementia risk later in life. The findings showed that people who sleep fewer than six hours per night already known to be at greater risk can meaningfully reduce that risk by replacing 30 minutes of inactivity or light activity with an extra half hour of sleep.
The study, led by Professor Matthew Pase and Dr Stephanie Yiallourou from the Turner Institute for Brain and Mental Health and the School of Psychological Sciences, was published in BMC Medicine. It explored how reallocating time between sleep, inactivity, light activity, and moderate-to-vigorous physical activity (MVPA) influenced dementia risk and brain volume. Participants (87,490 in total), drawn from UK Biobank, wore activity monitors for seven consecutive days at an average age of 63 and were followed for around eight years to track dementia diagnoses.
Among short sleepers (less than six hours per night), increasing sleep duration was linked to a lower dementia risk when it replaced inactivity or light activity but not when it replaced moderate-to-vigorous exercise. In contrast, for normal sleepers (six to nine hours per night), extending sleep at the expense of moderate or vigorous exercise was associated with a higher dementia risk, whereas increasing moderate-to-vigorous exercise instead of sleep was linked to reduced risk.
Similar patterns were observed in a subgroup of more than 15,000 participants who underwent brain MRI scans, with brain volume used as an additional marker of neurological health.
Overall, individuals who reported very short sleep, high levels of inactivity, and low moderate-to-vigorous activity showed the highest dementia rates and signs of accelerated brain aging on MRI.
For short sleepers specifically, replacing 30 minutes of inactivity with sleep was associated with a 9% reduction in dementia risk, while replacing light activity with sleep was linked to a 19% reduction. Interestingly, substituting sleep for light activity rather than inactivity appeared more beneficial. Dr Yiallourou suggested this may be because some periods classified as inactivity included cognitively engaging behaviors, such as reading, which could themselves support brain health.
Source: https://www.monash.edu/medicine/news/latest/2026-articles/monash-study-reveals-how-much-sleep-and-activity-a-person-needs-to-lower-dementia-risk
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