A lack of good quality sleep has long been linked to an increased risk of developing dementia, but recent research goes further, suggesting an optimal amount of overnight slumber to minimise dementia risk later in life, reports Science Alert.
Using data gathered and pooled from 69 previous studies, a team from York University in Canada ran a statistical analysis to look for associations with dementia for three different factors: physical activity, time spent sitting and sleep duration.
These are all variables we can control ourselves, up to a point, and the number crunching showed that between seven and eight hours of slumber each night was the sweet spot when it came to minimising dementia risk.
In addition, the researchers found that prolonged sitting (more than eight hours a day) and a lack of physical activity (less than 150 minutes a week) were also linked to a significant increase in the chances of getting dementia.
“Regular physical activity, less sedentary time and appropriate nightly sleep (seven to eight hours) may be associated with reduced risk of dementia and are potentially modifiable factors in the prevention or delay of dementia,” they wrote in their findings, published in PLOS One.
Having less than seven hours a night was linked to an 18% increase in dementia risk, while getting more than eight hours a night correlated to a 28% increase.
Those findings align with previous studies: getting too much sleep can be as harmful to our health as getting too little. The best target would be somewhere between seven and eight hours.
The researchers emphasised that their review doesn't prove cause and effect, though –these are associations, not direct connections.
What’s more, differentiating between triggers and consequences can be tricky: there’s research to suggest that sleeping too much is a sign that Alzheimer’s has already started, for example, and not just a driver for the disease.
Add in the physical activity connection and recommendations around sitting too much – both previously linked to issues with brain health – and it seems we have a collection of behaviours that are good for the brain.
Although the researchers didn’t conduct any testing themselves, they point to the benefits of exercise, regular movement, and sleep in maintaining active blood flow in the brain, clearing waste from neurons, and protecting other parts of the body linked to the brain (such as the heart).
With no cure yet available, and the number of dementia cases expected to keep on rising in the coming years, experts are keen to find ways for people to limit their chances of developing diseases like Alzheimer’s in the first place.
It’s estimated that around half of all cases could be avoided by addressing lifestyle risk factors.
“Taken together, a healthy movement behaviour profile may promote vascular, neurotrophic, and anti-inflammatory effects that collectively support brain health and may delay the onset or progression of dementia,” write the researchers.
One of the benefits of the research is the sheer number of people included: almost 4.5m, all told. It’s also notable that the data here cover people down to age 35, a much younger starting point than in many other studies on dementia.
All of the reviewed studies followed participants from a dementia-free starting point and then assessed the incidence of dementia over time.
However, there are limitations too. The reviewed studies varied significantly in terms of data collection and collation, and there were more figures on some behaviours than others – only three of the 69 studies looked specifically at sedentary habits, for example.
Gathering more data on the link between dementia risk and spending too much of the day sitting could be one avenue for future studies, the researchers suggest.
“Future studies with middle-aged adults and longer-term follow-up, including changes in movement behaviours over time, are needed to better understand the relationship between physical activity, sedentary behaviour, and sleep for dementia risk,” they wrote.
Study details
The Relationships between physical activity, sedentary behaviour, sleep, and dementia: A systematic review and meta-analysis of cohort studies
Akinkunle Oye-Somefun, Parmis Mirzadeh, Jenny Gao-Kang et al.
Published in PLOS One on 8 April 2026
Abstract
Objective
This study aimed to summarise the observational evidence from prospective cohort studies examining the associations of regular physical activity, sedentary behaviour, and sleep duration with incident dementia among community-dwelling adults aged 35 and older.
Methods
Systematic literature searches (1946 to August 2025) of CINAHL, EMBASE, MEDLINE, PSYCINFO, and SPORTDISCUS were performed. Eligible studies included community-dwelling adults aged 35 + years with at least one year of follow-up and valid measures of movement behaviours and dementia outcomes. Studies were excluded if they included participants with baseline dementia, lacked risk estimates for all-cause dementia. Grey literature was excluded. Random effects meta-analysis generated pooled risk ratio (RR) and 95% confidence intervals (CI). Primary exposures were defined using national thresholds for physical activity, sedentary time, and sleep duration. Subgroup analyses were performed by age and follow-up duration.
Results
Forty-nine studies with physical activity (n = 2,855,529), 17 studies on sleep duration (n = 1,344,170), and three studies on sedentary duration (n = 295,809) were included. Regular physical activity significantly reduced the risk of incident dementia (pooled RR = 0.75, 95% CI = 0.68 to 0.82), though heterogeneity was substantial and partially explained by subgroup analyses. Prolonged sedentary behaviour (8 + hours/day sitting) increased dementia risk (RR = 1.27, 95% CI = 1.17 to 1.39) with low heterogeneity. Moreover, both short (<7 hours; RR = 1.18, 95% CI = 1.09 to 1.28) and long (>8 hours; RR = 1.28, 95% CI = 1.15 to 1.43) sleep were linked to higher dementia risk compared with 7–8 hours. Heterogeneity was moderate to substantial.
Conclusion
Regular physical activity, less sedentary time and appropriate nightly sleep (7–8 h) may be associated with reduced risk of dementia and are potentially modifiable factors in the prevention or delay of dementia. Future studies with middle-aged adults and longer-term follow-up including changes in movement behaviours over time are needed to better understand the relationship between physical activity, sedentary behaviour, and sleep for dementia risk.
See more from MedicalBrief archives:
Seven hours is ideal amount of sleep in middle-age and older – UK-China study
Day-time sleepiness linked to Alzheimer’s risk
Sleep duration as risk factors for dementia and premature death
Under 7.32 hours’ sleep ideal for glucose disposal – Chinese study
Sleep catch-up does not reverse metabolic disruption from sleep loss