Lack of deep sleep increases Alzheimer’s risk study warns

Failing to spend sufficient time in the two deepest stages of sleep—slow-wave and rapid eye movement (REM) sleep—may accelerate the decline of brain regions linked to Alzheimer’s disease, according to new research.

The study, led by Gawon Cho, a postdoctoral associate in internal medicine at Yale School of Medicine, found that deficits in slow-wave and REM sleep appeared to cause shrinkage in parts of the brain associated with early cognitive decline.

“We found the volume of a part of the brain called the inferior parietal region shrunk in people with inadequate slow and REM sleep,” said Cho. “That part of the brain synthesises sensory information, including visuospatial information, so it makes sense that it shows neurodegeneration early in the disease.”

Dr Richard Issacson, a preventive neurologist and director of research at the Institute for Neurodegenerative Diseases in Florida, said his clinical experience reinforced the study’s conclusions. “We also found sleep metrics on deeper sleep predicted cognitive function, so between that plus brain volumes, it’s real,” he said.

Deep sleep plays a crucial role in brain health, helping to clear toxins and dead cells while repairing and restoring the body. Meanwhile, REM sleep is essential for processing emotions, consolidating memories, and absorbing new information.

Adults require around seven to eight hours of sleep per night, with roughly 20-25% spent in both deep and REM sleep. However, data from the US Centers for Disease Control and Prevention suggests that more than a third of American adults do not get enough rest.

To make matters worse, the amount of deep sleep naturally declines with age, Cho noted.

Since deep sleep occurs in the earlier part of the night and REM sleep later in the sleep cycle, cutting sleep short can significantly reduce the time spent in these restorative stages.

“The more time you are in bed, the more a person sleeps, and generally speaking, the longer a person sleeps, the more REM and deep sleep they will get,” Issacson explained.

However, simply spending more time in bed is not enough—sleep must also be uninterrupted and of high quality. Research published in February 2023 found that good sleep habits could extend life expectancy by nearly five years for men and 2.5 years for women.

To achieve this, experts recommend maintaining consistent sleep patterns, ensuring a cool and dark sleeping environment, and avoiding alcohol before bed. Disruptive habits such as exposure to blue light from screens should also be minimised in the hour before sleep.

“How do you make your sleep better? I think people really have to do their part to improve their own sleep,” Cho said. “There’s no one medicine that improves overall sleep.”