A recent study suggests that a warning sign may come before any symptoms of Alzheimer's disease: Adults who do not get enough deep sleep may be on their way to developing the disease.

Researchers from the Washington University School of Medicine in St. Louis, MO, found that older people who experience less slow-wave sleep (in other words, deep sleep) have elevated levels of a brain protein called tau. The findings, published in Translational Medicine, note that higher levels of tau are a sign of Alzheimer's disease. Elevated levels have also previously been associated with both brain damage and cognitive decline.

Slow-wave sleep and brain proteins

Slow-wave sleep helps people consolidate their memories and experiences, and getting enough of this type of sleep helps people wake up refreshed and energized. To find out if there is a connection between a lack of deep sleep and the development of Alzheimer's, the authors put together a study that involved 119 people aged 60 years or older.

A full 80% of the participants had no cognition problems, and the rest had only mild impairment. To conduct the study, researchers monitored their sleep at home over the course of a week. They gave each participant a portable electroencephalogram, or EEG, monitor that measured brain waves as they slumbered. The participants also wore a watch-like sensor to help track body movement. Additionally, they kept sleep logs that included how much they slept at night and whether they napped during the day.

The researchers also measured the amount of amyloid beta and tau in the brain and in the cerebrospinal fluid found around the brain and spinal cord. There were two ways to do this—38 people underwent positron-emission tomography (PET) brain scans, and 104 people underwent spinal taps, with 27 people doing both.

When they looked at the data collected, they found that those adults who experienced less slow-wave sleep had higher amounts of tau in the brain, and they also had a higher tau-to-amyloid ratio in their 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," noted first study author Dr. Brendan Lucey, director of the Washington University Sleep Medicine Center and an assistant professor of neurology. "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," he explained.

Alzheimer's disease

Alzheimer's disease is the most common form of dementia, according to the Alzheimer's Association. The term dementia describes memory loss and other cognitive problems that are serious enough to interfere with daily life. It is important to note that Alzheimer's is not a normal part of the aging process, and while most with the disease are aged over 65, it can occur in younger people. Alzheimer's is a progressive disease, which means that it gets worse over time and is the sixth most common cause of death in the US.

Mortality rates vary, with the average person living around 4–8 years after diagnosis. However, in some cases, a person with Alzheimer's can live 20 years after they've been diagnosed. There is currently no cure for the disease, but there are treatments available for symptoms. These treatments can often slow the progression of the disease, which makes early diagnosis crucial, and this is why research such as the recent study is so important.

What the future holds

Of course, research into Alzheimer's disease is ongoing, and Dr. Lucey admits that he does not expect sleep monitoring to replace traditional brain scans or cerebrospinal fluid analysis in regard to identifying early signs of Alzheimer's. However, this is something that caregivers and doctors can keep in mind as people grow older, even if they're not yet showing any signs of the disease.

"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."

—Dr. Brendan Lucey