Sleep is disrupted in people who likely have early Alzheimer's disease but do not yet have the memory loss or other cognitive problems characteristic of full-blown disease, researchers at Washington University School of Medicine in St. Louis report March 11 in JAMA Neurology .
The finding confirms earlier observations by some of the same researchers. Those studies showed a link in mice between sleep loss and brain plaques, a hallmark of Alzheimer's disease. Early evidence tentatively suggests the connection may work in both directions: Alzheimer's plaques disrupt sleep, and lack of sleep promotes Alzheimer's plaques.
Sleep problems are common in people who have symptomatic Alzheimer's disease, but scientists recently have begun to suspect that they also may be an indicator of early disease. The new paper is among the first to connect early Alzheimer's disease and sleep disruption in humans.
For the new study, researchers recruited 145 volunteers from the University's Charles F. and Joanne Knight Alzheimer's Disease Research Center. All of the volunteers were 45 to 75 years old and cognitively normal when they enrolled.
As a part of other research at the center, scientists already had analyzed samples of the volunteers' spinal fluids for markers of Alzheimer's disease. The samples showed that 32 participants had preclinical Alzheimer's disease, meaning they were likely to have amyloid plaques present in their brains but were not yet cognitively impaired.
Participants kept daily sleep diaries for two weeks, noting the time they went to bed and got up, the number of naps taken on the previous day, and other sleep-related information.
The researchers tracked the participants' activity levels using sensors worn on the wrist that detected the wearer's movements.
"Most people don't move when they're asleep, and we developed a way to use the data we collected as a marker for whether a person was asleep or awake," says first author Yo-El Ju, MD, assistant professor of neurology. "This let us assess sleep efficiency, which is a measure of how much time in bed is spent asleep."
Participants who had preclinical Alzheimer's disease had poorer sleep efficiency (80.4 percent) than people without