We’ve long known that a lack of quality nighttime sleep is linked to a higher risk of developing dementia. A team of researchers at York University in Canada set out to identify the optimal amount of nighttime sleep to protect against dementia later in life.
How much sleep protects against dementia
The university team focused on results from 69 previous studies. In particular, they ran a statistical analysis of the data to identify the relationship between dementia and three variables:
- physical activity
- time spent sitting
- sleep duration
All of these factors are things people can control themselves.
One advantage of the new work is the huge number of participants: about 4.5 million. It’s also important that the sample included people younger than 35, much younger than participants in many other dementia studies.
The analysis showed that the optimal nighttime sleep to minimize the risk of developing dementia is 7–8 hours.
The researchers also found that prolonged sitting (more than 8 hours per day) and insufficient physical activity (less than 150 minutes per week) are associated with a higher probability of developing dementia.
Regular matters because its health effects carry over into sleep. It helps:
- support active blood circulation in the brain
- clear waste from neurons
- protect other parts of the body connected to the brain, such as the heart
Sleeping less than 7 hours per day correlates with an 18% increased risk of developing dementia. Meanwhile, sleeping more than 8 hours is associated with a 28% increase in that risk.
Other key findings from the study
These conclusions align with earlier studies, particularly the idea that too much sleep can be just as harmful to health as too little.
Separating triggers from consequences can be difficult. For example, excessive sleepiness can be a sign that Alzheimer’s disease has already started, not just a factor that increases the risk of the disease.
Because there are no drugs yet to treat dementia, and experts predict case numbers will rise in the coming years, scientists are looking for more accessible strategies to reduce the likelihood of developing dementia, especially lifestyle changes.
In the paper published in PLOS One, the team wrote: “Healthy movement produces vascular, neurotrophic, and anti-inflammatory effects that together support brain health and slow the onset or progression of dementia.”
The team believes one direction for future research should be collecting additional data on the link between dementia risk and excessively long periods of sitting during the day.
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