Poor sleep is a hallmark of Alzheimer’s disease. People with the disease tend to wake up tired, and their nights become even less refreshing as memory loss and other symptoms worsen. But how and why restless nights are linked to Alzheimer’s disease is still not fully understood.
Now, researchers at Washington University School of Medicine in St. Louis may have uncovered part of the explanation. They found that older people who have less slow-wave sleep – the deep sleep you need to consolidate memories and wake up feeling refreshed – have higher levels of the brain protein tau. Elevated tau is a sign of Alzheimer’s disease and has been linked to brain damage and cognitive decline.
“What’s interesting is that we saw this inverse relationship between decreased slow-wave sleep and more tau protein in people who were either cognitively normal or very mildly impaired, meaning that reduced slow-wave activity may be a marker for the transition between normal and impaired,” said first author Brendan Lucey, MD, an assistant professor of neurology and director of the Washington University Sleep Medicine Center. “Measuring how people sleep may be a noninvasive way to screen for Alzheimer’s disease before or just as people begin to develop problems with memory and thinking.”
The brain changes that lead to Alzheimer’s, a disease that affects an estimated 5.7 million Americans, start slowly and silently. Up to two decades before the characteristic symptoms of memory loss and confusion appear, amyloid beta protein begins to collect into plaques in the brain. Tangles of tau appear later, followed by atrophy of key brain areas. Only then do people start showing unmistakable signs of cognitive decline.
The challenge is finding people on track to develop Alzheimer’s before such brain changes undermine their ability to think clearly. For that, sleep may be a handy marker.
If future research bears out their findings, sleep monitoring may be an easy and affordable way to screen earlier for Alzheimer’s disease, the researchers said. Daytime napping alone was significantly associated with high levels of tau, meaning that asking a simple question – How much do you nap during the day? – might help doctors identify people who could benefit from further testing.
“I don’t expect sleep monitoring to replace brain scans or cerebrospinal fluid analysis for identifying early signs of Alzheimer’s disease, but it could supplement them,” Lucey said. “It’s something that could be easily followed over time, and if someone’s sleep habits start changing, that could be a sign for doctors to take a closer look at what might be going on in their brains.”