A lack of deep sleep at night and daytime napping may signal changes in the brain that are characteristic of Alzheimer’s disease.
By the time the early signs of Alzheimer’s disease are apparent, it could already be too late for doctors to step in to slow the progression of the disease. That’s the reason researchers are looking for means to identify the early stages of Alzheimer’s disease (AD) before any symptoms develop.
The findings of a study published on January 9 in the journal Science Translational Medicine suggest that altered sleep patterns may be a signal that the brain changes associated with Alzheimer’s are occurring.
Search from the Washington University Sleep Medicine Center and the Charles F. and Joanne Knight Alzheimer’s Disease Research Center (ADRC) in St. Louis have found that older adults who have less slow-wave sleep — the deep sleep you need to process long-term memories and wake up feeling refreshed — have higher levels of the brain protein tau, which is a sign of Alzheimer’s disease and has been associated with brain damage and cognitive decline.
Slow-Wave Activity Decreased With Increased Tau
“In our research, we measured slow-wave activity during non–rapid eye movement sleep, the deepest stage of which is slow-wave sleep … and we observed that slow-wave activity decreased with increased tau,” says the lead author Brendan P. Lucey, MD, an assistant professor of neurology and the director of the sleep medicine section at Washington University School of Medicine.
“Since issues with thinking and memory starts as tau increases, we think that slow-wave activity will be an important marker for Alzheimer’s disease [and] that changes in the brain during Alzheimer’s disease, especially tau accumulation, will disrupt normal slow-wave activity either before or soon after problems with thinking and memory start,” Dr. Lucey says.
Most Study Participants Cognitively Normal or Only Mildly Impaired
Lucey and his colleague David Holtzman, MD, the Andrew B. and Gretchen P. Jones Professor of Neurology at Washington University School of Medicine, recruited 119 adults age 60 or older through the ADRC, although most (80 percent) were “cognitively normal” at the time they were enrolled in the study. The rest were very mildly impaired, according to Lucey.
Drs. Lucey and Holtzman asked the study participants to self-monitor their sleep, at home, over the course of a normal week, using a portable EEG monitor to measure their brain waves and a wristwatch-like sensor to track body movement. Study participants were also asked to maintain sleep logs, in which they recorded nighttime sleep and daytime napping.
Meanwhile, the researchers measured levels of amyloid beta, a protein linked with Alzheimer’s disease, and tau in the brain and analyzed the cerebrospinal fluid of study participants using PET brain scans and spinal taps.
‘How Much Do You Sleep During the Day?’ May Be a Useful Screening Question
After controlling for factors such as sex and age, they found that decreased slow-wave sleep coincided with higher levels of tau in the brain and a higher tau-to-amyloid ratio in the cerebrospinal fluid.
Daytime napping alone was significantly associated with higher levels of tau, meaning that the question, “How much do you nap during the day?” may help doctors identify people who could benefit from further testing for cognitive decline. In fact, if future research echoes their findings, Lucey and Holtzman believe sleep monitoring may be an easy and affordable way to screen for AD.
Added Benefits to Sleep Monitoring
According to Lucey, several studies have found links between sleep disturbances and the changes seen in the brain with AD.
“I think that the type of sleep monitoring that may play a future role in screening for Alzheimer’s disease still needs to be worked out, but we think slow-wave activity is a potentially sensitive marker worth pursuing in future studies,” he says.
“Sadly, research has not yet shown that treating sleep disorders will decrease someone’s risk of Alzheimer’s disease. However, as a sleep physician, I recommend that anyone with sleep problems should be evaluated [for Alzheimer’s or cognitive decline]. Sleep disturbances have been associated with heart disease, diabetes, and other chronic diseases in addition to Alzheimer’s disease.”