Excessive Daytime Sleepiness Associated With Alzheimer’s Risk, Long-term Study Reports

Excessive daytime sleepiness or napping is associated with increased beta-amyloid plaques in the brain, a major characteristic of Alzheimer’s disease, according to a study that followed patients for more than 15 years.

The study, “Excessive daytime sleepiness and napping in cognitively normal adults: associations with subsequent amyloid deposition measured by PiB PET,” was published in the journal Sleep. 

Factors such as diet, exercise, and cognitive activities such as doing puzzles or crosswords are important potential targets for Alzheimer’s disease prevention.

Sleep, on the other hand, has not been widely associated with Alzheimer’s disease. However, a lack of sleep has been linked to cognitive impairment and decline.

Researchers from the Johns Hopkins Bloomberg School of Public Health, the National Institute on Aging, and Johns Hopkins Medicine conducted a study aimed at better understanding if excessive daytime sleepiness (EDS) and napping are markers of subsequent Alzheimer’s risk.

The team analyzed data from the Baltimore Longitudinal Study of Aging Neuroimaging Study — a long-term study that began in 1958 and followed the health of thousands of participants as they aged.  At the time of enrollment, participants were considered healthy.

As part of the study’s periodic exams, participants were asked to fill out a questionnaire (between 1991 and 2000) that included questions such as, “Do you often become drowsy or fall asleep during the daytime when you wish to be awake?” or “Do you nap?” Based on the answers, participants were characterized as having EDS or by their napping habits.

The study included a subset of participants who began neuroimaging assessments in 1994, which are still ongoing. In 2005, some of these volunteers also started receiving positron emission tomography (PET) scans using a radioactive compound that can help identify beta-amyloid plaques in brain tissue.

Researchers studied 123 participants with self-reported measures of EDS or napping, had a PET scan, and who were cognitively normal at sleepiness and napping assessment. At enrollment, the average age of participants was 60.1 years, ranging from 36.2 to 82.7. Slightly more than half of the participants were women (50.8%), and 21.8% were non-white.  PET imaging was performed an average of 15.7 years after enrollment, ranging between 6.9 and 24.6 years.

Researchers found that participants with reported EDS were about three times more likely to have beta-amyloid plaques present on their PET scans (56.7%) than those who were not very sleepy during the day. After adjusting for other factors that could influence the risk of Alzheimer’s such as age, sex, education, and body-mass index, those that reported EDS were still at a 2.75 times higher risk of developing beta-amyloid plaques than those without excessive daytime sleepiness.

This trend was also true for people who reported napping more during the day, although it did not reach statistical significance.

Despite these results, it’s still not entirely clear how sleep contributes to the formation of beta-amyloid plaques. Because PET scans were not performed at enrollment, researchers cannot rule out that beta-amyloid plaques were present before people reported feeling sleepy.

However, animal studies using Alzheimer’s disease models have shown that restricting nighttime sleep can increase the deposition of beta-amyloid protein in the brain and spinal fluid, suggesting that sleep is a contributing factor to beta-amyloid plaque formation. In addition, some human studies have linked poor sleep and higher levels of beta-amyloid in neuronal tissue.

These results suggest that increasing sleep quality by targeting conditions that affect sleep, such as obstructive sleep apnea and insomnia, or social factors such as sleep loss due to work or binge-watching TV shows, “may have important implications for Alzheimer’s prevention,” the researchers said.

“If disturbed sleep contributes to Alzheimer’s disease, we may be able to treat patients with sleep issues to avoid these negative outcomes,” study author Adam P. Spira, PhD, an associate professor in the Department of Mental Health at the Bloomberg School, said in a press release.