Alzheimer’s is the main cause of cognitive decline in older adults, contributing to about 70 percent of dementia cases. Poor sleep is a common symptom of the disease and a driving force that can accelerate the disease’s progression. A new study has found the ideal sleeping time to help reduce your risk.
A multiyear study of older adults found that both short and long sleepers experienced greater cognitive decline than people who slept a moderate amount, even when the effects of early Alzheimer’s disease were taken into account.
The study, which was published in the journal, Brain, was led by researchers at Washington University School of Medicine in St. Louis.
Poor sleep and Alzheimer’s disease are both associated with cognitive decline and separating out the effects of each has proven challenging.
By tracking cognitive function in a large group of older adults over several years and analysing it against levels of Alzheimer’s-related proteins and measures of brain activity during sleep, the researchers generated crucial data that help untangle the complicated relationship among sleep, Alzheimer’s and cognitive function.
The researchers found a U-shaped relationship between sleep and cognitive decline.
Overall, cognitive scores declined for the groups that slept less than 4.5 or more than 6.5 hours per night while scores stayed stable for those in the middle of the range.
Tiny electroencephalogram monitors (EEG) findings showed 5.5 to 7.5 hours of self-reported sleep being the sweet spot.
“It was particularly interesting to see that not only those with short amounts of sleep but also those with long amounts of sleep had more cognitive decline,” said co-senior author doctor David Holtzman, a professor of neurology.
“It suggests that sleep quality may be key, as opposed to simply total sleep.”
“It’s been challenging to determine how sleep and different stages of Alzheimer’s disease are related, but that’s what you need to know to start designing interventions,” said first author doctor Brendan Lucey, an associate professor of neurology and director of the Washington University Sleep Medicine Center.
“Our study suggests that there is a middle range, or ‘sweet spot,’ for total sleep time where cognitive performance was stable over time.
“Short and long sleep times were associated with worse cognitive performance, perhaps due to insufficient sleep or poor sleep quality.
“An unanswered question is if we can intervene to improve sleep, such as increasing sleep time for short sleepers by an hour or so, would that have a positive effect on their cognitive performance, so they no longer decline? We need more longitudinal data to answer this question.”
Each person’s sleep needs are unique, and people who wake up feeling rested on short or long sleep schedules should not feel compelled to change their habits, added doctor Lucey.
“But those who are not sleeping well should be aware that sleep problems often can be treated.”
“I ask many of my patients, ‘How’s your sleep?’” said co-senior author doctor Beau An, Professor of Neurology.
“Often patients report that they’re not sleeping well. Often once their sleep issues are treated, they may have improvements in cognition.
“Physicians who are seeing patients with cognitive complaints should ask them about their quality of sleep. This is potentially a modifiable factor.”
Other possible risk factors
There are different types of risk factors for dementia, including medical, lifestyle and environmental factors.
Some factors only slightly increase a person’s risk while others make it much more likely that the person will develop the condition.
“For most people, the biggest risk factors for dementia are ageing and genes,” warns the Alzheimer’s Society (AS).
It is worth noting that there are lots of risk factors that can be avoided, or at least reduced.
“Doing regular physical activity is one of the best ways to reduce your risk of dementia. It’s good for your heart, circulation, weight and mental wellbeing,” notes the AS.