Scientists have recently shown that both the quality and the amount of sleep we get may influence our risk of developing Alzheimer's disease.
Now, a study suggests that people who take significantly longer to start the dream phase of sleep, known as rapid eye movement (REM), may be experiencing an early symptom of the disease.
REM follows three phases of non-REM sleep, each deeper than the last. The four phases take 90 minutes or more to complete, depending on age, and a person may cycle through them four or five times in a typical night. Older people take longer to reach REM.
During REM sleep the brain processes memories, especially those that are emotionally charged, and puts them into long-term storage.
"The delay in REM sleep disrupts the brain's ability to consolidate memories by interfering with the process that contributes to learning and memory," said Yue Leng , PhD, an associate professor in the Department of Psychiatry and Behavioral Sciences at UCSF.
"If it is insufficient or delayed, it may increase the stress hormone cortisol," said Leng, who is part of the UCSF Weill Institute for Neurosciences . "This can impair the brain's hippocampus, a critical structure for memory consolidation."
Leng is a senior author of the paper, which appears Jan. 27 in Alzheimer's and Dementia: The Journal of the Alzheimer's Association .
Higher levels of amyloid, tau
Researchers followed 128 people with an average age of 70 from the neurology unit of the China-Japan Friendship Hospital in Beijing. Half had Alzheimer's, and about one-third had mild cognitive impairment, a frequent precursor to Alzheimer's. The rest had normal cognition.
The participants in the study slept overnight in the clinic, so researchers could measure their brainwave activity, eye movement, heartrate and breathing. Fitness trackers can capture some of this information, but it is less precise.
The researchers divided the participants into early and delayed REM sleep. On average, the early group reached REM less than 98 minutes after falling asleep, while the late group reached it more than 193 minutes after falling asleep.
Those with Alzheimer's were more likely to have delayed REM sleep, and they also tended to have higher levels of the two toxic proteins, amyloid and tau, found in people with the condition.
Those with delayed REM sleep had 16% more amyloid and 29% more tau than those with early REM sleep. They also had 39% less of a healthy protein called brain derived neurotrophic factor (BDNF), which drops in Alzheimer's.
"Future research should study the effects of certain medications that influence sleep patterns, as these may modify disease progression," Leng said.
Melatonin can boost REM sleep, and studies in mice have shown that it decreases tau and amyloid accumulation. Other drugs that treat insomnia by blocking a chemical that suppresses REM sleep also have been shown to decrease tau and amyloid.
People who are concerned about their risk for Alzheimer's should practice healthy sleep habits that facilitate the transition from light sleep to REM sleep. "This includes treating conditions like sleep apnea and avoiding heavy drinking, since both can interfere with a healthy sleep cycle," said Dantao Peng, MD, of the Department of Neurology at the China-Japan Friendship Hospital in Beijing, who is also a senior author of the paper.
"Patients taking certain antidepressants and sedatives that reduce REM sleep should discuss their concerns with their doctor, if they are worried about Alzheimer's."
Authors: Co-first authors are Jiangli Jin, MD, of China-Japan Friendship Hospital and the School of Clinical Medicine in Beijing, and Jiong Chen of the Institute of Medical Technology, Peking University Health Science Center. For a complete list of authors, please see the paper.
Funding: Chinese Ministry of Science and Technology (grant # 2021ZD0201902) and the Chinese National Health Commission (grant# 2020ZD10).
About UCSF: The University of California, San Francisco (UCSF) is exclusively focused on the health sciences and is dedicated to promoting health worldwide through advanced biomedical research, graduate-level education in the life sciences and health professions, and excellence in patient care. UCSF Health , which serves as UCSF's primary academic medical center, includes top-ranked specialty hospitals and other clinical programs, and has affiliations throughout the Bay Area. UCSF School of Medicine also has a regional campus in Fresno. Learn more at ucsf.edu , or see our Fact Sheet .
