Sleep loss can be an early warning sign of Alzheimer's, new research suggests.
The findings, from a study of healthy volunteers, point the way to new methods of detecting and monitoring the disease, say scientists.
Evidence indicates that the link between sleep and Alzheimer's runs in two directions. Alterations in the brain caused by the disease disrupt sleep, and poor sleep also promotes the changes.
Professor David Holtzmann, from Washington University School of Medicine, said: "This link may provide us with an easily detectable sign of Alzheimer's.
"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 treatments are succeeding."
Sleep problems are common among people with full-blown Alzheimer's. The new research suggests they may also be a sign of early-developing disease and symptoms to come.
Animal studies conducted on mice have demonstrated a link between sleep loss and beta-amyloid plaques – lumps of protein in the brain that are a hallmark of Alzheimer's disease.
People with early signs of Alzheimer's spent the same amount of time in bed as non-affected volunteers, but did not sleep as long. They also napped more often.