During slow-wave or deep sleep, the brain is cleared of waste products.
A single night of disrupted sleep is enough to increase a brain protein linked to Alzheimer’s, new research shows.
A full week of poor sleep causes increases in another brain protein that is also linked to Alzheimer’s.
The findings may help to explain why poor sleep has been linked to Alzheimer’s.
Professor David M. Holtzman, who led the study, said:
“We showed that poor sleep is associated with higher levels of two Alzheimer’s-associated proteins.
We think that perhaps chronic poor sleep during middle age may increase the risk of Alzheimer’s later in life.”
Alzheimer’s disease is characterised by gradual cognitive decline and memory loss.
Previous research has shown a link between poor sleep and cognitive problems.
For example, people with sleep apnea — when breathing stops repeatedly during the night — are at risk of developing mild cognitive impairment ten years earlier.
For the study, the effects of sleep apnea were simulated.
People’s deep sleep was disrupted in such a way that they did not wake during the night, but they also did not feel refreshed in the morning.
Levels of the two proteins — called amyloid beta and tau — were both measured by spinal taps.
Dr Yo-El Ju, the study’s first author, explained the results:
“We were not surprised to find that tau levels didn’t budge after just one night of disrupted sleep while amyloid levels did, because amyloid levels normally change more quickly than tau levels.
But we could see, when the participants had several bad nights in a row at home, that their tau levels had risen.”
The scientists do not think that one night or a week of poor sleep is enough to cause Alzheimer’s.
The protein levels probably return to normal with better sleep.
Dr Ju said:
“The main concern is people who have chronic sleep problems.
I think that may lead to chronically elevated amyloid levels, which animal studies have shown lead to increased risk of amyloid plaques and Alzheimer’s.”
It is vital that we get enough slow-wave or deep sleep, as this is when the brain is cleared of waste products.
Dr Ju said:
“Many, many Americans are chronically sleep-deprived, and it negatively affects their health in many ways.
At this point, we can’t say whether improving sleep will reduce your risk of developing Alzheimer’s.
All we can really say is that bad sleep increases levels of some proteins that are associated with Alzheimer’s disease.
But a good night’s sleep is something you want to be striving for anyway.”
The study was published in the journal Brain (Ju et al., 2017).