Could there be a link between cognitive decline and excessive daytime napping? New research from the Rush Alzheimer鈥檚 Disease Center suggests a potential connection, according to an article published in Alzheimer鈥檚 and Dementia: The Journal of the Alzheimer鈥檚 Association in March.
The connection appears to occur in both directions, researchers say; longer and more frequent napping was correlated with worse cognition after one year, and worse cognition was correlated with longer and more frequent naps after one year.
, a neurologist at 海角原创 and co-author of the article, said the study lends evidence to the changing views of Alzheimer鈥檚 disease as a purely cognitive disorder.
鈥淲e now know that the pathology related to cognitive decline can cause other changes in function,鈥 he said. 鈥淚t鈥檚 really a multi-system disorder, also including difficulty sleeping, changes in movement, changes in body composition, depression symptoms, behavioral changes, etc.鈥
Researchers followed more than 1,400 patients for up to 14 years as part of the Rush and the Participants wore a wrist-worn sensor that recorded activity continuously for up to 10 days, and came in once a year for examinations and cognitive testing. Any prolonged period of no activity during the daytime from 9 a.m. to 7 p.m. was considered a nap.
When the study started, more than 75% of participants showed no signs of any cognitive impairment, 19.5% had mild cognitive impairment and slightly more than 4% had Alzheimer's disease dementia. Daily napping increased by about 11 minutes per year among those who didn't develop cognitive impairment during follow-up. Naps doubled after a diagnosis of mild cognitive impairment, and nearly tripled after a diagnosis of Alzheimer's disease dementia.
Researchers also compared participants who had normal cognition at the start of the study but developed Alzheimer's disease dementia to their counterparts whose thinking remained stable during the study. They found that older people who napped more than an hour a day had a 40% higher risk of developing Alzheimer's.
Buchman stressed that the study does not imply that napping causes Alzheimer鈥檚 dementia, or vice versa.
鈥淭his is an observational study, so we can鈥檛 say that 鈥榓 causes b鈥,鈥 he said. 鈥淏ut we can say that they unfold at the same time, and it鈥檚 possible that the same pathologies may contribute to both.鈥
Alzheimer鈥檚 disease is caused by the accumulation of two proteins, amyloid beta and tau, within the brain. While the decline in cognitive function is the most well-known symptom of Alzheimer鈥檚 disease, this protein accumulation can occur in various locations of the brain, brainstem and spinal cord, causing a variety of symptoms. The study indicates that increases in the frequency and duration of daytime napping may be one of those symptoms.
鈥淥nce you鈥檝e identified the pathology and location, you can work on potential treatments,鈥 Buchman said. 鈥淭here are proteins or genes that might prevent the accumulation of tau and beta, or there鈥檚 potentially ways to mitigate or slow their accumulation.鈥
The study was supported by the National Institutes of Health and the BrightFocus Foundation Alzheimer鈥檚 Research Program. Buchman said that one of the study鈥檚 primary strengths was its participant cohorts from the Memory and Aging Project and the Religious Order Study. Both studies are decades-long efforts that recruit participants to undergo annual testing, sample collection and organ donation after their death.
鈥淭he people in our studies are very special people,鈥 he said. 鈥淲ithout people making this kind of contribution we wouldn鈥檛 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鈥檙e very lucky to have them.鈥
