Persistent daytime drowsiness may be a warning sign for Alzheimer’s disease, a new study suggests. During sleep, the brain clears away clumps of a sticky protein linked to dementia, called amyloid. It’s well known that people with Alzheimer’s often have trouble sleeping. To examine the link between amyloid deposits and sleep, Mayo Clinic researchers surveyed 283 older people without dementia about their sleep habits and monitored their brains for amyloid buildup over a period of seven years. They found those who reported trouble sleeping, with frequent daytime sleepiness, were more likely to show rapid amyloid plaque accumulation than those who didn’t. Study author Prashanthi Vemuri tells Time.com that the results highlight the importance of proper sleep. “It can prevent amyloid, which is one of the primary proteins underlying Alzheimer’s disease,” he says.