A poor night’s sleep may increase the levels of proteins associated with Alzheimer’s disease, say researchers, noting that their findings may be especially important for people with chronic sleep disorders.
The study by scientists at Stanford University, Washington University School of Medicine in St. Louis and Radboud University Medical Centre in the Netherlands, “Slow wave sleep disruption increases cerebrospinal fluid amyloid-β levels,” appeared in the journal Brain.
“We showed that poor sleep is associated with higher levels of two Alzheimer’s-associated proteins,” Dr. David M. Holtzman and the study’s senior researcher, said in a news release. “We think that perhaps chronic poor sleep during middle age may increase the risk of Alzheimer’s later in life.”
Previous studies had shown that lack of sleep increases the production of beta-amyloid, suggesting that patients who suffer chronic sleep deprivation may be at high risk of Alzheimer’s.
However, researchers did not know exactly what aspect of sleep is associated with beta-amyloid levels and other disease biomarkers.
To find out, the study enrolled 17 healthy adults (aged 35 to 65 years) with no sleep or cognitive disorders. Researchers analyzed brain wave activity during a polysomnogram, which uses a wrist monitor to record a person’s sleep.
After five or more successive nights wearing the monitor, participants were invited to spend a night in a sleep room designed for the study. Half of them, however, were assigned to have their sleep disturbed while a monitor recorded sleep-induced brain waves and how they changed when sleep was somehow interrupted.
Researchers also collected samples of cerebrospinal fluid, looking for changes in the levels of proteins linked to Alzheimer’s such as tau and beta-amyloid.
One month later, they repeated the experiment, but this time, those who had slept uninterrupted had their sleep disturbed during the night, while participants who had not slept so well were now allowed to have a peaceful night.
Results showed that changes in slow wave activity led to a 10 percent increase in amyloid beta levels after a single night of interrupted sleep. Although tau protein didn’t go up, participants who slept poorly in the week before fluid sample collection presented increased levels of the protein.
“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,” said Yo-El Ju, the study’s first author. “But we could see, when the participants had several bad nights in a row at home, that their tau levels had risen.”
She said it is unlikely that a single night or week of poor sleep has much impact on the overall risk of Alzheimer’s. But for those with chronic sleep deprivation, the story may be different.
“The main concern is people who have chronic sleep problems,” Ju said. “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.”
“Many, many Americans are chronically sleep-deprived, and it negatively affects their health in many ways,” she added. “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.”