A common sleep habit could be a warning sign of Alzheimer's and dementia, according to a new study.
Brief naps help us recharge and face the day and all the stresses and strains that come with adult life. They're particularly important as we get older, but longer and more frequent daytime napping could be linked to a higher risk of Alzheimer's dementia.
This can be a "vicious cycle", with the condition causes more napping, potentially leading to worse symptoms of dementia. The researchers, who published their findings in the Alzheimer's & Dementia journal, wrote: "Older adults tended to nap longer and more frequently with aging, while the progression of Alzheimer's dementia accelerates this change by more than doubling the annual increases in nap duration/frequency.
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In the study, researchers from looked at data from 1,401 people who they followed up for up to 14 years. Participants had an average age of 81, and roughly three quarters of them were women. They were asked to wear a watch-like device on their non-dominant wrist, to calculate the length and frequency of naps, for two weeks every year, and each year they underwent a range of tests to assess cognitive skills.
While three in four participants had no cognitive impairment, and only 4.1 percent had Alzheimer's disease, at the start of the study, there was a marked relationship between napping and the condition's development. Participants who napped at least once a day had a 40 per cent higher risk of developing Alzheimer's than those who napped less than this, Hull Daily Mail reports.
For participants who did not develop cognitive impairment, daily daytime napping increased by an average 11 minutes per year. The rate of increase doubled after a diagnosis of mild cognitive impairment to 24 minutes and nearly tripled to 68 minutes after a diagnosis of Alzheimer's disease.
Dr Peng Li, the first author in the study, said: "Daytime sleep behaviours of older adults are oftentimes ignored, and a consensus for daytime napping in clinical practice and health care is still lacking. Our results not only suggest that excessive daytime napping may signal an elevated risk of Alzheimer's dementia, but they also show that faster yearly increase in daytime napping may be a sign of deteriorating or unfavoured clinical progression of the disease.
"Our study calls for a closer attention to 24-hour sleep patterns, not only night-time sleep but also daytime sleep, for health monitoring in older adults. The vicious cycle we observed between daytime sleep and Alzheimer's disease offers a basis for better understanding the role of sleep in the development and progression of Alzheimer's disease in older adults."
Senior co-author Dr Yue Leng said: "We found the association between excessive daytime napping and dementia remained after adjusting for night-time quantity and quality of sleep. This suggested that the role of daytime napping is important itself and is independent of night-time sleep.
“The study shows for the first time that napping and Alzheimer's disease seem to be driving each other's changes in a bi-directional way. I don't think we have enough evidence to draw conclusions about a causal relationship, that it's the napping itself that caused cognitive aging, but excessive daytime napping might be a signal of accelerated aging or cognitive aging process.
"It would be very interesting for future studies to explore whether intervention of naps may help slow down age-related cognitive decline."
The study, published in Alzheimer's & Dementia in March 2022, was a collaboration between between Brigham and Women's Hospital in Boston, the Rush Alzheimer's Disease Centre in Chicago and the University of California, San Francisco.
