A night spent tossing and turning doesn’t just affect short-term memory, mood and the next day’s caffeine intake. Missing out on deep sleep has also been linked to an increased risk for Alzheimer’s disease, according to a study released by Washington University School of Medicine in St. Louis.
After studying 119 people ages 60 and older, researchers determined people who experienced less deep sleep—characterized by slow brain waves necessary to process memories and wake up well rested—had more of the protein tau in their brains. Accumulated tau is associated with Alzheimer’s disease, with some researchers believing that the build-up of tau is behind the cognitive problems of neurodegenerative diseases like Alzheimer’s.
It’s difficult for studies like this one to show whether a lack of deep sleep causes a tau buildup or if a tau buildup causes restless sleep, but this study does point out that trouble sleeping could be a very early warning sign for cognitive problems in older adults.
“We saw this inverse relationship between decreased slow-wave sleep and more tau protein in people who were either cognitively normal or very mildly impaired, meaning that reduced slow-wave activity may be a marker for the transition between normal and impaired,” said study author Dr. Brendan Lucey, an assistant professor of neurology and director of the Washington University Sleep Medicine Center.
Researchers suggested sleep could aid in screening people for Alzheimer’s—a disease with a history of misdiagnosis that currently require expensive and invasive tests for diagnosis.
“Measuring how people sleep may be a noninvasive way to screen for Alzheimer’s disease before or just as people begin to develop problems with memory and thinking,” Lucey said in a statement.
That would be helpful because almost all clinical trials searching for a cure for Alzheimer’s are now looking for people without major symptoms of Alzheimer’s who are in the very early stages of the disease.
In the study, almost all patients—about 80 percent—were cognitively normal. They were monitored with an EEG attached to their foreheads and with a wrist sensor to record brain waves as they slept. They also kept a sleep diary, with each person producing between two and six nights of data. When scientists compared the numbers of beta-amyloid, another protein associated with Alzheimer’s, and tau in the brain before and after the study, those with less evidence of slow-wave sleep had more tau in the brain and a higher tau-to-amyloid ratio in their cerebrospinal fluid.
“The key is that it wasn’t the total amount of sleep that was linked to tau, it was the slow-wave sleep, which reflects quality of sleep,” Lucey said. “The people with increased tau pathology were actually sleeping more at night and napping more in the day, but they weren’t getting as good quality sleep.”
It’s not more sleep that was associated with a risk of Alzheimer’s, but better sleep. People who took naps during the day also showed higher levels of tau.
Researchers hope that this finding will help frame how doctors assess their patients for potential cognitive impairment.
“I don’t expect sleep monitoring to replace brain scans or cerebrospinal fluid analysis for identifying early signs of Alzheimer’s disease, but it could supplement them,” Lucey said. “It’s something that could be easily followed over time, and if someone’s sleep habits start changing, that could be a sign for doctors to take a closer look at what might be going on in their brains.”