• Posted January 28, 2025

Delayed Dream Sleep Linked to Alzheimer's Risk

Delays in dreaming might be an early warning sign of Alzheimer’s disease.

People who take significantly longer to enter the rapid eye movement (REM) phase of sleep could be experiencing an early symptom of Alzheimer’s, researchers reported Jan. 27 in the journal Alzheimer’s & Dementia.

“The delay in REM sleep disrupts the brain’s ability to consolidate memories by interfering with the process that contributes to learning and memory,” senior researcher Yue Leng, an associate professor in the University of California-San Francisco’s Department of Psychiatry and Behavioral Sciences, said in a news release.

“If it is insufficient or delayed, it may increase the stress hormone cortisol,” she said. “This can impair the brain’s hippocampus, a critical structure for memory consolidation.”

Previous studies have shown that both the quality and amount of sleep people get can influence their risk of Alzheimer’s.

For this study, researchers focused on REM sleep, because during this phase, the brain processes memories -- particularly those that are emotionally charged -- and puts them into long-term storage.

While people sleep, the REM phase tends to occur after three phases of non-REM sleep that are each deeper than the last, researchers said.

These four phases take 90 minutes or more to complete, depending on age, and a person might cycle through them four to five times during a typical night, researchers said.

Older people tend to take longer to reach REM, researchers noted.

For this study, researchers tracked 128 people with an average age of 70 who were being treated in the neurology unit of the China-Japan Friendship Hospital in Beijing.

Half the patients had Alzheimer’s, and a third had mild cognitive impairment, a type of mental decline that itself is a warning sign for Alzheimer’s.

All participants slept overnight in the clinic so researchers could track their brainwave activity, eye movement, heart rate and breathing.

The research team then divided patients into two groups, based on whether they entered REM sleep earlier or later than average.

On average, the early group entered REM less than 98 minutes after falling asleep, while the late group reached it more than 193 minutes into their slumber.

Those with Alzheimer’s were more likely to have delayed REM sleep, and they also had higher levels of the toxic brain proteins associated with the disorder, amyloid and tau.

People with delayed REM sleep also had higher levels of the toxic proteins – 16% more amyloid and 29% more tau – than those with early REM sleep, results show.

Further, delayed REM sleep also was associated with 39% lower levels of a healthy brain protein called brain derived neurotrophic factor (BDNF), whose levels drop in Alzheimer’s patients.

However, the study couldn’t say in which direction the association runs -- whether people developing Alzheimer’s have delayed dream sleep, or whether poor dreaming increases Alzheimer’s risk.

It could be that better sleep might help ward off Alzheimer’s, researchers said, noting earlier mouse research that linked use of the sleep supplement melatonin with decreased tau and amyloid levels.

Other studies also have found that drugs that treat insomnia by blocking a chemical that suppresses REM sleep also decreases tau and amyloid, researchers added.

“Future research should study the effects of certain medications that influence sleep patterns, as these may modify disease progression,” Leng said.

In the meantime, people worried about their brain health should practice good sleep hygiene, researchers said.

“This includes treating conditions like sleep apnea and avoiding heavy drinking, since both can interfere with a healthy sleep cycle,” senior researcher Dr. Dantao Peng, a neurologist with China-Japan Friendship Hospital, said in a news release.

“Patients taking certain antidepressants and sedatives that reduce REM sleep should discuss their concerns with their doctor, if they are worried about Alzheimer’s,” Peng added.

More information

The Sleep Foundation has more on the stages of sleep.

SOURCE: University of California-San Francisco, news release, Jan. 27, 2025