In a new study, researchers at Washington University School of Medicine in St. Louis may have uncovered important explanation on how and why poor sleep is linked to early signs of Alzheimer’s disease.
Older people who have reduced slow-wave sleep – the deep sleep required to accumulate memories and wake up feeling refreshed – tend to have higher percentage of the brain protein tau, according to the researchers. Elevated tau has not only been associated with memory loss, confusion, and brain damage but also been considered as a sign of Alzheimer’s disease.
Findings of the study, appeared recently in Science Transitional Medicine, suggest that poor-quality sleep in later life could a warning sign of deteriorating brain health.
Most interestingly, the team observed an inverse relationship between reduced slow-wave sleep and increased tau protein in people who were cognitively normal or mildly impaired, indicating that decreased slow-wave sleep could be a marker for the transition from normal cognition to impaired one.
According to Brendan Lucey, MD, first author and assistant professor of neurology, measuring the way people sleep would be a noninvasive method to check for Alzheimer’s disease before and as the people start to have issues with memory and thinking.
Changes in the brain that lead to Alzheimer’s disease, affecting an estimated 5.7 million US population, begin slowly and silently. Up to two decades, amyloid beta proteins begin to consolidate into plaques in the brain, before the distinctive symptoms of confusion and memory loss appear. Tau proteins tangled up much later, followed by deterioration of key brain regions. Only then do people start showing the critical symptoms of cognitive decline.
It has been a challenge detect people who are likely to develop Alzheimer’s, prior to changes in the brain that limits the ability to think clearly.
For better understanding of the relationship between sleep and Alzheimer’s disease, the team examined 119 study participants 60 years of age or above. Of which, around 80% were cognitively normal, while the remaining ones were very mildly impaired.
The researchers monitored the volunteers’ sleep at home over the course of a normal week. To measure the brain waves, the participants were provided a portable EEG monitor strapped on their foreheads and for wristwatch-like sensor for tracking the body movement. Additionally, they kept a sleep log, noting down nighttime sleep sessions as well as daytime napping.
The researchers also measured levels of tau protein and amyloid beta in the brain and in the cerebrospinal fluid. Of all the participants, 38 underwent brain PET scan for the two proteins, 104 underwent spinal taps, and 27 did both.
After controlling for different factors such as age, sex, and sleep movements, the researchers discovered that reduced slow-wave sleep associated with elevated tau in the brain and a high ratio of tau-to-amyloid in the cerebrospinal fluid.
Lucey said that the important observation is that the total amount of sleep was not linked to tau, but rather the slow-wave sleep, reflecting the quality of sleep. If future research confirms their results, sleep monitoring may contribute as a simple and affordable way to screen earlier of Alzheimer’s disease, the researchers said.