Dementia is an umbrella term for a group of symptoms associated with an ongoing decline of brain functioning. Alzheimer’s disease makes up the majority of cases of dementia in the UK. The first sign of Alzheimer’s disease is usually minor memory problems. Recent research shows how poor sleeping patterns may be a red flag too.
It has previously been revealed that 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 has not been fully understood.
The recent findings, published in Science Translational Medicine, provides an insight into this grey area. The researchers found that older people who have less slow-wave sleep – the deep sleep a person needs to consolidate memories and wake up feeling refreshed – have higher levels of the brain protein tau.
As Alzheimers UK explained, Alzheimer’s disease results from the build-up of two proteins in the brain; toxic tau tangles inside of the cell and amyloid plaques outside of it.
“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.
She added: “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.”
To better understand the link between sleep and Alzheimer’s disease, Lucey, along with David Holtzman, MD, the Andrew B. and Gretchen P. Jones Professor and head of the Department of Neurology, and colleagues studied 119 people 60 years of age or older who were recruited through the Charles F. and Joanne Knight Alzheimer’s Disease Research Center.
Most – 80 per cent – 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.
Participants were given a portable EEG monitor that strapped to their foreheads to measure their brain waves as they slept, as well as a wristwatch-like sensor that tracks body movement.
They also kept sleep logs, where they made note of both nighttime sleep sessions and daytime napping. Each participant produced at least two nights of data; some had as many as six.
The researchers also measured levels of amyloid beta and tau in the brain and in the cerebrospinal fluid that bathes the brain and spinal cord.
Thirty-eight people underwent PET brain scans for the two proteins, and 104 people underwent spinal taps to provide cerebrospinal fluid for analysis. Twenty-seven did both.
After controlling for factors such as sex, age and movements while sleeping, the researchers 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 quality of sleep,” Lucey said.
He added: “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.”
According to the NHS, other progressive symptoms of Alzheimer’s disease include:
- Confusion, disorientation and getting lost in familiar places
- Difficulty planning or making decisions
- Problems with speech and language
- Problems moving around without assistance or performing self-care tasks
- Personality changes, such as becoming aggressive, demanding and suspicious of others
- Hallucinations (seeing or hearing things that are not there) and delusions (believing things that are untrue)
- Low mood or anxiety