Researchers repeated the experiment about a month later but switched the groups. After each night, doctors gave the participants, who ranged from 35 to 65, a spinal tap to collect samples of their cerebrospinal fluid, which surrounds the brain. Tests on those samples showed nine participants had higher levels of beta amyloid after sleep disruptions, and the increases were greater in those whose sleep was more disturbed.
“When we did not let their brain cells rest by giving them all those beeps, then they continued to produce as much amyloid as in lighter sleep or wakefulness,” Ju says.
In addition, participants wore devices on their wrists to help measure their sleep at home during the days before the procedure. People whose devices pointed to worse sleep had higher levels of tau proteins, the study reports.
“These were normal, healthy, young or middle-aged people,” Ju says. “They have no sleep disorders. Even in this very healthy population, we see variations in their sleep at home that does affect tau and amyloid levels.”
'Impressive' Findings
Alzheimer’s is a brain disease that gets worse over time. It robs people of their memories and mental abilities. Although beta amyloid and tau are associated with the disease, not everyone who has these proteins in their brain gets Alzheimer’s.
More than 5 million people are now battling the illness in the United States, and it has become the sixth-leading cause of death. The cost of caring for Alzheimer’s patients is expected to top $250 billion this year.
Previous studies in animals have pointed toward a link between slow-wave sleep and higher amyloid levels, says Adam Spira, PhD, a clinical psychologist who studies sleep, aging, and Alzheimer’s at the Johns Hopkins Bloomberg School of Public Health in Baltimore.
The new study shows the same sort of results in humans, but more studies are needed to figure out the mechanism behind those results, he says.
“It’ll be interesting to see whether disruption of other specific sleep stages leads to smaller increases or no increases,” Spira says.