Ju can't say exactly how much more likely the diagnosis was in those who woke up often.
Those who spent less than 85% of their time in bed actually sleeping were also more likely to have preclinical Alzheimer's disease, they found.
About half of the group had more than five awakenings an hour, and about half spent less than 85% of their time in bed sleeping, Ju says.
While waking up five times an hour sounds like a lot, she says the sleep-measuring device may slightly overestimate the number of awakenings, but that ''people actually do wake briefly quite frequently during a regular night of sleep."
Ju cites animal studies finding that sleep changes drive the accumulation of amyloid. She suspects that is the case for people, too.
"But more study is needed," she says. "We don't have any information that tells us which direction the association is."
Meanwhile, getting a good night's sleep is advised. "Everyone should prioritize their sleep," Ju says. "We don't value sleep as much as we should. Sleep is a very important function that allows the brain to rest."
Sleep Problems and Alzheimer's Link? More Opinions
"This [study] is another indication there are early brain changes [in Alzheimer's disease]," says Maria Carrillo, PhD, senior director of medical and scientific relations for the Alzheimer's Association.
Which way the association develops is yet to be determined, she says.
"The trouble sleeping could reflect brain changes happening," Carrillo tells WebMD.
The study finding is not surprising, says UCLA's Small. "We know that getting a good night's sleep is important for the brain."
Of the new research, "the causal relationship is not clear," he says.
He suspects that inflammation may be playing a role. He and other experts believe brain inflammation and Alzheimer's may be linked. Perhaps the lack of sleep increases inflammation, he says. Small serves as speaker or advisor for Novartis, Forest, and Lilly.
The study was funded by the nonprofit Ellison Medical Foundation and the National Institutes of Health.
This study is due to be presented at a medical conference. The findings should be considered preliminary as they have not yet undergone the "peer review" process, in which outside experts scrutinize the data prior to publication in a medical journal.