People with Alzheimer’s often have troubled sleep patterns, waking up many times during the night or sleeping on and off throughout the day. Now, new research suggests that problems with sleep may be among the earliest signs of Alzheimer’s, occurring years before memory loss and other symptoms become evident.
In the latest study, researchers at Washington University School of Medicine in St. Louis worked with mice that had been specially bred to develop a disease resembling Alzheimer’s in people. They found that disruptions of the sleep cycle corresponded with the first appearance of plaques in the brain. Plaques, a hallmark of Alzheimer’s disease, are composed of beta-amyloid, a toxic protein that builds up in the brains of those with Alzheimer’s. Beta-amyloid begins to aggregate in the brain long before symptoms of Alzheimer’s appear.
"If sleep abnormalities begin this early in the course of human Alzheimer's disease, those changes could provide us with an easily detectable sign of pathology," said study author Dr. David M. Holtzman. "As we start to treat Alzheimer's patients before the onset of dementia, the presence or absence of sleep problems may be a rapid indicator of whether the new treatments are succeeding." The findings appeared in the journal Science Translational Medicine.
Doctors increasingly believe that Alzheimer’s may be a decades-long process and are searching for ways to detect the disease in its earliest stages, when it may be most treatable. Sleep problems could provide an early clinical clue that Alzheimer’s may be beginning, though many older people have insomnia and other sleep problems without having dementia. Further research would be needed to distinguish between ordinary insomnia and sleep troubles related to Alzheimer’s.
In the current study, the researchers found that mice with brain plaques slept less than those without the plaques. Mice are normally active during the night, and during the day sleep for about 40 minutes of every hour. When Alzheimer's plaques began forming in their brains, their average sleep times dropped to 30 minutes per hour. Mice that were given a vaccine that prevented the buildup of beta-amyloid plaques, on the other hand, had normal sleep patterns as they aged.
Scientists are now studying whether sleep problems occur in patients who have markers of Alzheimer's disease, such as plaques in the brain, but have not yet developed memory or thinking problems.
"If these sleep problems exist, we don't yet know exactly what form they take -- reduced sleep overall or trouble staying asleep or something else entirely," Dr. Holtzman said. "But we're working to find out."
Other research has linked sleep problems to Alzheimer’s onset. An earlier study from Washington University, for example, found that men who wake up many times during the night – more than five times per hour – were more likely to be in the earliest stages of Alzheimer’s than those who slept soundly. Another large study of women found that those who slept fewer than five hours or more than nine hours a night were at higher risk of cognitive decline than those who slept seven hours a night. And sleep apnea, a common breathing disorder in which people stop breathing for short periods hundreds of times during the night, has been linked to memory decline and dementia. [See the alzinfo.org story, “Common Sleep Problem Linked to Dementia” at http://www.alzinfo.org/11/articles/diagnosis-and-causes/common-sleep-problem-linked-dementia .]
Anyone can suffer from sleep problems at any age, and poor sleep is by no means a predictor of Alzheimer’s in most people, though it can interfere with quality of life. If you suffer from sleep difficulties or suspect that breathing problems during sleep may be contributing to memory and thinking problems, it is important to discuss this with your doctor. Effective treatments are available.
Source: Washington Unviersity in St. Louis. J. H. Roh, Y. Huang, A. W. Bero, et al: “Disruption of the Sleep-Wake Cycle and Diurnal Fluctuation of Beta-Amyloid in Mice with Alzheimer's Disease Pathology.” Science Translational Medicine, 2012; Vol. 4 (150).