In a study from Washington University in St. Louis, scientists 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.
The findings suggest that poor-quality sleep in later life could be a red flag for deteriorating brain health.
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 not fully understood.
The brain changes that lead to Alzheimer’s 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.
In the study, the team tested 119 people 60 years of age or older. Most—80 percent—were cognitively normal, and the remainder were very mildly impaired.
The researchers monitored the participants’ sleep at home over the course of a normal week.
They found that decreased slow-wave sleep coincided with higher levels of tau in the brain and a higher tau-to-amyloid ratio in the cerebrospinal fluid.
The key is that it wasn’t the total amount of sleep that was linked to tau, it was the slow-wave sleep, which reflects the quality of sleep.
The people with increased tau pathology were actually sleeping more at night and napping more in the day, but they weren’t getting as good quality sleep.
The team says sleep monitoring may be an easy and affordable way to screen earlier for Alzheimer’s disease.
Daytime napping alone was strongly linked to 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.
If you care about Alzheimer’s disease, please read about studies about a new biomarker of Alzheimer’s disease, and these two old drugs may help treat Alzheimer’s disease.
For more information about brain health, please see recent studies about why some older people less likely to have Alzheimer’s disease, and results showing this daily habit may help treat Alzheimer’s disease.
The study was conducted by Brendan Lucey et al and published in Science Translational Medicine.
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