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Disrupted sleep may be an indication of early Alzheimer's disease, according to a new study.

Researchers at Washington University School of Medicine in St. Louis found that sleep is disrupted in people who likely have early Alzheimer's disease but do not yet have the memory loss of other cognitive problems characteristic of full-blown disease.

The findings, published March 11 in JAMA Neurology, confirms earlier findings from previous studies linking sleep loss and Alzheimer's brain plaques in mice.  Researchers found that 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," researcher Dr. David M. Holtzman, the Andrew B. and Gretchen P. Jones Professor and head of Washington University's Department of Neurology, said in a statement. "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."

While sleep problems are common in people with symptomatic Alzheimer's disease, researchers are beginning to suspect that sleep disruption may also be an indicator of early disease.

The study involved 145 volunteers from the University's Charles F. and Joanne Knight Alzheimer's Disease Research Center. The participants were 45 to 75 years old and were cognitively normal at the start of the study.

Scientists also analyzed samples of the participants' spinal fluids for markers of Alzheimer's disease.  Researchers said the samples showed that 32 participants had preclinical Alzheimer's disease, which meant they probably had amyloid plaques present in their brains but were not yet cognitively impaired.

Participants were asked to keep daily sleep diaries for two weeks.  They had to write down the time they went to bed and got up, the number of naps taken on the previous day and other sleep-related information.  Researchers also monitored 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," first author Dr. Yo-El Ju, said in a statement. "This let us assess sleep efficiency, which is a measure of how much time in bed is spent asleep."

The findings revealed that participants who had preclinical Alzheimer's disease had poorer sleep efficiency at 80.4 percent than people without markers of Alzheimer's at 83.7 percent. Researcher found that all participants spent the same amount of time in bed, but those with preclinical disease spent less time asleep.  These people also napped more often.  

"When we looked specifically at the worst sleepers, those with a sleep efficiency lower than 75 percent, they were more than five times more likely to have preclinical Alzheimer's disease than good sleepers," Ju said.

Next, researchers hope to conduct studies in younger participants with sleep disorder.

"We think this may help us get a better feel for the way this connection flows - does sleep loss drive Alzheimer's, does Alzheimer's lead to sleep loss, or is it a combination?" Ju added. "That will help us determine whether we can change the course of disease with pharmaceuticals or other treatments."