One of the earliest signs of Alzheimer’s disease could be how well you sleep at night, even when no other memory problems seem evident, a new study suggests.

Researchers from the Washington University School of Medicine in St. Louis found that sleep efficiency is slightly worse among people with preclinical Alzheimer’s disease, compared with those without the condition. Sleep efficiency is defined as the ability to sleep throughout the night, with minimal disruptions.

“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?” study researcher Dr. Yo-El Ju, M.D., an assistant professor of neurology at the university, said in a statement. “That will help us determine whether we can change the course of disease with pharmaceuticals or other treatments.”

The study, published in the journal JAMA Neurology, included 145 people between ages 45 and 75 who were part of the Charles F. and Joanne Knight Alzheimer’s Disease Research Center at the university. When they enrolled in the study, none of them had any cognitive issues. However, their spinal fluid was analyzed, and researchers found that about one-third of them were very likely to have Alzheimer’s-linked amyloid plaques in the brain (considered preclinical Alzheimer’s).

The researchers had the study participants keep a sleep diary — where they tracked their bedtimes, wake times and naps — and wear special wrist sensors to detect movement (including movement when awake versus movement when asleep) for two weeks.

Researchers found that those with the evidence of preclinical Alzheimer’s had worse sleep efficiency than those with no evidence of it — 80.4 percent versus 83.7 percent. Plus, those with evidence of preclinical Alzheimer’s spent less time actually sleeping when they were in bed than those without it, even though the two groups spent the same amount of time in bed.

Those who were the least efficient sleepers in the whole study — meaning their sleep efficiency was less than 75 percent — were also the ones with a five times higher risk of having preclinical Alzheimer’s, the researchers noted.

This is hardly the first time sleep woes haven been linked with Alzheimer’s. Researchers from the same university reported last year in the journal Science their findings that mice with Alzheimer’s-linked plaques also experienced abnormalities in their sleeping patterns when the plaques were developing.

Plus, a study presented at the Alzheimer’s Association International Conference last year showed an association between sleeping fewer or more than seven hours a night in women, and an effect on the beta amyloid 42/40 ratio, which is an early sign of Alzheimer’s disease.