Sleep loss can be an early warning sign of Alzheimer's, new research suggests.
The findings, from a study of apparently healthy volunteers, point the way to new methods of detecting the disease, say scientists.
Evidence indicates the link between sleep and Alzheimer's runs in two directions.
Alterations in the brain caused by the disease may disrupt sleep, and poor sleep promotes the changes.
Lead scientist Professor David Holtzmann, from Washington University School of Medicine in the US, said: "This link may provide us with an easily detectable sign of Alzheimer's pathology.
"As we start to treat people who have markers of early Alzheimer's, changes in sleep in response to treatments may indicate of whether the new treatments are succeeding."
Sleep problems are common among people with Alzheimer's. The study suggests they may be a sign of early-developing disease and symptoms to come.
Previous 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.
The research involved 145 people aged 45 to 75 who were showing no signs of memory loss when enrolled.
Analysis of samples of the volunteers' spinal fluid showed that 32 participants had molecular markers of pre-symptomatic Alzheimer's, according to the research published in the journal JAMA Neurology
The volunteers kept daily sleep diaries for two weeks, noting what time they went to bed and got up, the number of naps they took during the day, and other relevant information.
Participants who had pre-clinical Alzheimer's had a "sleep efficiency" of 80.4%, compared with an average 83.7% for those without Alzheimer's markers.
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.
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