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.
That's the word from researchers at Washington University School of Medicine in St. Louis, who discovered 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.
"This link may provide us with an easily detectable sign of Alzheimer's pathology," says senior author and neurologist David M. Holtzman, M.D. "As we start to treat people who have markers of early Alzheimer's, changes in sleep in response to treatments may serve as an indicator of whether the new treatments are succeeding."
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; however, this is the first study to connect early Alzheimer's disease and sleep disruption in humans.
The study: The team recruited 145 volunteers from the Alzheimer's research center at Washington University. At the beginning of the study, all were between the ages of 45 and 75 years old and cognitively normal. Because the volunteers were all part of the ongoing Alzheimer's disease research at the university, scientists had already analyzed samples of their spinal fluids, looking specifically for markers of Alzheimer's. Those samples showed that 32 of the study participants had preclinical Alzheimer's disease, which means they were likely to have amyloid plaques present in their brains but were not yet cognitively impaired.
In addition, the volunteers 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 Yo-El Ju, M.D., assistant professor of neurology. "This let us assess sleep efficiency, which is a measure of how much time in bed is spent asleep."
The results: Those who had preclinical Alzheimer's disease had poorer sleep efficiency (80.4 percent) than people without markers of Alzheimer's (83.7 percent). On average, those with preclinical disease were in bed as long as other participants, but they spent less time asleep. They also napped more often.
The bottom line: Those who slept the worst were five times more likely to have preclinical Alzheimer's disease than good sleepers.
The study findings were published in the journal JAMA Neurology.
--From the Editors at Netscape