Consistently sleeping for more than eight and a half hours each night could be associated with early changes in the brain linked to Alzheimer's disease, according to new research.
The study, published in the journal Alzheimer's & Dementia, analyzed data from 2,410 participants in the Framingham Heart Study, who had an average age of 70.
Researchers found that individuals who reported sleeping longer than 8.5 hours per night had elevated blood levels of p-tau181, a biomarker known to be strongly associated with Alzheimer's disease. The levels of this biomarker appeared to increase more rapidly among those who slept over ten hours a night.
These findings persisted even after the researchers accounted for other factors such as age, sex, sleep apnea, and depression. The study authors suggest that self-reported sleep durations of nine to ten hours or more nightly may merit further evaluation of sleep and cognitive health.
"We knew from the existing literature that the relationship between sleep and these biomarkers was unlikely to be simple, and that’s exactly what we found," said Dr. Vanessa Young, lead author of the study and a postdoctoral research fellow at the Glenn Biggs Institute for Alzheimer’s and Neurodegenerative Diseases at UT Health San Antonio.
Scientists emphasized that the study does not indicate that longer sleep causes Alzheimer's disease. Instead, they propose that extended sleep could be an early behavioral sign of underlying neurodegeneration. The researchers noted that long-term studies are necessary to fully understand the relationship between sleep duration and the progression of Alzheimer's disease.
This research adds to previous studies that have indicated a connection between both short and long sleep durations and Alzheimer's disease, which is the most common cause of dementia. Current NHS guidelines recommend that adults up to age 65 should aim for seven to nine hours of sleep per night, while those over 65 should get seven to eight hours.
Dementia affects approximately one million people in the UK, with about one in 14 individuals over the age of 65 experiencing the condition. The disease can impair language, reasoning, memory, and the ability to perform daily tasks.