Recent research has uncovered compelling connections between sleep disturbances and early signs of Alzheimer's disease, suggesting that disrupted sleep patterns may serve as important biomarkers for cognitive decline risk.
A study published January 27, 2025, in the journal Alzheimer's & Dementia reveals that delayed entry into rapid eye movement (REM) sleep—the dream phase of sleep—could be an early warning sign of Alzheimer's disease. Researchers from the University of California-San Francisco tracked 128 participants with an average age of 70, half of whom had Alzheimer's disease and a third with mild cognitive impairment.
"The delay in REM sleep disrupts the brain's ability to consolidate memories by interfering with the process that contributes to learning and memory," explained senior researcher Yue Leng, an associate professor in UCSF's Department of Psychiatry and Behavioral Sciences.
Participants who took longer to enter REM sleep—more than 193 minutes after falling asleep compared to the early group's average of less than 98 minutes—showed significantly higher levels of toxic brain proteins associated with Alzheimer's. Specifically, those with delayed REM sleep had 16% more amyloid and 29% more tau protein compared to those with early REM sleep.
Additionally, delayed REM sleep was associated with 39% lower levels of brain-derived neurotrophic factor (BDNF), a healthy brain protein that typically decreases in Alzheimer's patients.
Daytime Drowsiness Signals Pre-Dementia Condition
In a separate but related study published November 6, 2024, in the journal Neurology, researchers identified another sleep-related warning sign for cognitive decline. The study found that seniors experiencing excessive daytime sleepiness and lack of enthusiasm were more than three times more likely to develop motoric cognitive risk syndrome—a pre-dementia condition characterized by slow walking speed and memory problems.
Dr. Victoire Leroy from the Albert Einstein College of Medicine in New York City and colleagues followed 445 people with an average age of 76 for approximately three years. They discovered that about 36% of seniors with excessive daytime sleepiness and diminished enthusiasm developed the syndrome, compared to only 7% of those without these sleep-related issues.
"Our findings emphasize the need for screening for sleep issues," Leroy stated. "There's potential that people could get help with their sleep issues and prevent cognitive decline later in life."
Potential Mechanisms and Implications
While the exact causal relationship between sleep disturbances and Alzheimer's remains unclear, researchers have proposed several mechanisms. Leng suggests that insufficient or delayed REM sleep may increase cortisol levels, potentially impairing the hippocampus—a brain structure critical for memory consolidation.
During normal sleep architecture, people cycle through four sleep phases approximately four to five times during a typical night, with REM sleep occurring after three progressively deeper phases of non-REM sleep. This cycle typically takes 90 minutes or more to complete, with older adults naturally taking longer to reach REM.
Previous animal studies have shown promising connections between sleep interventions and reduced Alzheimer's pathology. Research with mice has linked melatonin supplementation with decreased tau and amyloid levels. Similarly, medications that treat insomnia by blocking chemicals that suppress REM sleep have been found to decrease these toxic proteins.
Clinical Recommendations
While more research is needed to fully understand the relationship between sleep disturbances and cognitive decline, experts recommend several practical steps for maintaining brain health:
- Practice good sleep hygiene
- Treat underlying sleep disorders such as sleep apnea
- Avoid heavy alcohol consumption, which can interfere with healthy sleep cycles
- Discuss concerns about medications that may reduce REM sleep, such as certain antidepressants and sedatives, with healthcare providers
"Patients taking certain antidepressants and sedatives that reduce REM sleep should discuss their concerns with their doctor, if they are worried about Alzheimer's," advised Dr. Dantao Peng, a neurologist with China-Japan Friendship Hospital and senior researcher on the REM sleep study.
These findings highlight the importance of quality sleep as a potentially modifiable risk factor for cognitive decline. As research continues to explore the mechanisms linking sleep disturbances to Alzheimer's disease and pre-dementia conditions, sleep assessment may become an increasingly valuable tool for early detection and intervention strategies.
