Research suggests that an early sign of dementia could be disrupted sleep patterns.
Sleep is disrupted in people who are likely have early Alzheimer's disease but do not yet have the memory loss or other cognitive problems characteristic of full-blown disease, explain researchers in a statement.
"This link may provide us with an easily detectable sign of Alzheimer's pathology," say researchers from the Washington University School of Medicine.
"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."
More ways that sleep affects your wellbeing..
For the study, 145 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," said Yo-El Ju, assistant professor of neurology, in a statement.
"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%) than people without markers of Alzheimer's (83.%).
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.
"When we looked specifically at the worst sleepers, those with a sleep efficiency lower than 75%, they were more than five times more likely to have preclinical Alzheimer's disease than good sleepers," Ju said.
Early evidence also tentatively suggests that just as Alzheimer's plaques disrupt sleep, so a lack of sleep could promote Alzheimer's plaques.
"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 said.
"That will help us determine whether we can change the course of disease with pharmaceuticals or other treatments."