Could there be a connection between cognitive decline and excessive daytime napping?
New research from the Rush Alzheimer’s Disease Center suggests a potential link, according to an article published recently in Alzheimer’s and Dementia: The Journal of the Alzheimer’s Association.
According to the researchers, the link appears to be reciprocal: lower cognition was associated with longer and more frequent naps after one year, and worse cognition was associated with longer and more frequent naps after one year.
The study gives weight to the evolving perspectives of Alzheimer's disease as a solely cognitive issue, according to Aron Buchman, MD, a neurologist at Rush University Medical Center and co-author of the publication.
“We now know that the pathology related to cognitive decline can cause other changes in function,” he added. “It’s really a multi-system disorder, also including difficulty sleeping, changes in movement, changes in body composition, depression symptoms, behavioral changes, etc.”
In the Rush Memory and Aging Project and the Religious Order Study, researchers tracked over 1,400 patients for up to 14 years. Participants wore a wrist-worn sensor that continually collected activity for up to 10 days and were examined and tested once a year. A nap was defined as any period of inactivity between 9 a.m. and 7 p.m. during the day.
More than 75% of patients had no symptoms of cognitive impairment when the trial began, 19.5 percent had moderate cognitive impairment, and slightly more than 4% had Alzheimer's disease dementia. Those who did not suffer cognitive impairment during follow-up increased their daily napping by roughly 11 minutes each year. Naps approximately quadrupled following a diagnosis of Alzheimer's disease dementia, and nearly doubled after a diagnosis of moderate cognitive impairment.
Participants who had normal cognition at the start of the trial but acquired Alzheimer's disease dementia were compared to those whose thinking stayed steady throughout the study. They discovered that elderly persons who slept for more than an hour every day had a 40% increased risk of Alzheimer's disease.
The study, according to Buchman, does not prove that sleeping causes Alzheimer's disease or vice versa.
“This is an observational study, so we can’t say that ‘a causes b’,” he explained. “But we can say that they unfold at the same time, and it’s possible that the same pathologies may contribute to both.”
Amyloid beta and tau protein buildup in the brain causes Alzheimer's disease. While the most well-known sign of Alzheimer's disease is a deterioration in cognitive function, protein buildup can occur in a number of places throughout the brain, brainstem, and spinal cord, resulting in a wide range of symptoms. Increased daytime napping frequency and length may be one of those signs, according to the research.
“Once you’ve identified the pathology and location, you can work on potential treatments,” Buchman says. “There are proteins or genes that might prevent the accumulation of tau and beta, or there’s potentially ways to mitigate or slow their accumulation.”
The study was supported by the National Institutes of Health and the BrightFocus Foundation Alzheimer’s Research Program. One of the study's main advantages, according to Buchman, was the inclusion of participant cohorts from the Memory and Aging Project and the Religious Order Study. Both studies are multi-decade endeavors in which people are recruited to endure yearly examination, sample collection, and organ donation after death.
“The people in our studies are very special people,” he remarked. “Without people making this kind of contribution, we wouldn’t be able to do the research that we do. They are so excited to be able to participate, they animate the staff with their participation. We’re very lucky to have them.”
