Lack of deep sleep could lead to dementia but there's an easy remedy, study finds

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Scientists studying the links between sleep and dementia have found evidence that one type of sleep, so-called slow wave or deep sleep, is crucial for reducing the risk of dementia in old age.

The research, published in JAMA Neurology (part of the Journal of the American Medical Association), looked at long-term data from 346 participants of the Framington Heart Study, a multi-generational study of cardiovascular disease and other health issues that’s been ongoing since 1948.

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The team of researchers from Australia, Canada and the United States chose participants, roughly equal numbers of men and women, who had completed two overnight sleep study sessions in the late 1990s and early 2000s, and who were over 60 years old in 2020.

“We used these to examine how slow-wave sleep changed with aging and whether changes in slow-wave sleep percentage were associated with the risk of later-life dementia up to 17 years later,” neuroscientist Matthew Pase of Monash University in Melbourne told the website sciencealert.com.

Of the 346 participants, 52 were found to have developed dementia. But while the average amount of slow-wave sleep in all participants was found to decrease from age 60 onward – with the loss peaking between 75 and 80 before levelling off – the researchers also noticed that each percentage point decrease in slow-wave sleep per year corresponded with a 27 per cent increase in the risk of dementia.

For Alzheimer’s, the most common form of dementia, the risk was even higher at 32 per cent.

The authors of the study also noted that this doesn’t prove that slow-wave sleep loss causes dementia. Correlation is not causation as the saying goes, and it’s possible that dementia causes a decrease in slow-wave sleep, and not the other way around.

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But it’s worth noting that another study released earlier this year by researchers at the University of California Berkeley, UC Irvine and Stanford found that people with brain changes associated with Alzheimer’s performed better on memory function tests if they got more deep sleep. This would suggest that, even if slow-wave sleep can’t prevent dementia, it could lessen the effects.

Slow-wave sleep is the third of four stages of sleep, and precedes the better-known REM or rapid-eye movement stage, which is when we dream. During the deep sleep stage, brain waves slow, along with heart rate, blood pressure and breathing. People are typically harder to wake during this stage.

Although not fully understood, deep sleep seems to affect learning, memory, tissue growth and repair, and expelling waste products from the fluid around the brain.

For anyone worried at this point about getting enough slow-wave sleep, science has a simple solution: Wear a mask. Eye masks of the type worn to sleep on airplanes have been found to increase the amount of time spent in slow-wave sleep and, not surprisingly, to improve memory and alertness the following day.

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