A new study shows that older adults who report being very sleepy during the day were nearly three times more likely to have brain deposits of beta amyloid, a protein that’s a hallmark for Alzheimer’s disease, years later.
The long-term study, published in the journal SLEEP, adds to the evidence that getting adequate night-time sleep could be a way to help prevent Alzheimer’s disease.
“Factors like diet, exercise, and cognitive activity have been widely recognized as important potential targets for Alzheimer’s disease prevention, but sleep hasn’t quite risen to that status, although that may well be changing,” said Adam P. Spira, Ph.D., an associate professor in the Department of Mental Health at the Johns Hopkins Bloomberg School of Public Health.
“If disturbed sleep contributes to Alzheimer’s disease, we may be able to treat patients with sleep issues to avoid these negative outcomes,” added Spira, who led the study with collaborators from the National Institute on Aging (NIA), the Bloomberg School, and Johns Hopkins Medicine.
The study used data from the Baltimore Longitudinal Study of Aging (BLSA), a long-term study started by the NIA in 1958 that followed the health of thousands of volunteers as they age.
As part of the study’s periodic exams, volunteers completed a questionnaire between 1991 and 2000 that asked a simple question: “Do you often become drowsy or fall asleep during the daytime when you wish to be awake?”
They were also asked, “Do you nap?” with response options of “daily,” “1-2 times/week,” “3-5 times/week,” and “rarely or never.”
A subgroup of participants in the BLSA study also began receiving neuroimaging assessments in 1994. Starting in 2005, some of these participants received positron emission tomography (PET) scans using Pittsburgh compound B (PiB), a radioactive compound that can help identify beta-amyloid plaques in neuronal tissue. These plaques are a hallmark of Alzheimer’s disease, the researchers explained.
The researchers identified 123 volunteers who both answered the earlier questions and had a PET scan with PiB an average of nearly 16 years later. They then analyzed this data to see if there was a correlation between participants who reported daytime sleepiness or napping and whether they scored positive for beta-amyloid deposition in their brains.
Before adjusting for demographic factors that could influence daytime sleepiness, such as age, sex, education, and body-mass index, their results showed that those who reported daytime sleepiness were about three times more likely to have beta-amyloid deposition than those who didn’t report daytime fatigue. After adjusting for these factors, the risk was still 2.75 times higher in those with daytime sleepiness, the researchers report.
The unadjusted risk for amyloid-beta deposition was about twice as high in volunteers who reported napping, but this did not reach statistical significance, the researchers noted.
According to Spira, it’s unclear why daytime sleepiness would be correlated with the deposition of beta-amyloid protein.
One possibility is that daytime sleepiness itself might somehow cause this protein to form in the brain.
Based on previous research, a more likely explanation is that disturbed sleep — due to obstructive sleep apnea, for example — or insufficient sleep due to other factors causes beta-amyloid plaques to form through a currently unknown mechanism, and that these sleep disturbances also cause excessive daytime sleepiness.
“However, we cannot rule out that amyloid plaques that were present at the time of sleep assessment caused the sleepiness,” he added.
Researchers have long known that sleep disturbances are common in patients diagnosed with Alzheimer’s disease. Caregiver stress from being up with patients at night is a leading reason for Alzheimer’s disease patients to be placed in long-term care, Spira explained. Growing beta-amyloid plaques and related brain changes are thought to negatively affect sleep, he said.
But this new study adds to growing evidence that poor sleep might actually contribute to Alzheimer’s disease development, Spira added.
This suggests that sleep quality could be a risk factor that’s modifiable by targeting disorders that affect sleep, such as obstructive sleep apnea and insomnia, as well as social- and individual-level factors, such as sleep loss due to work or binge-watching TV shows, he said.