(ORDO NEWS) — Prolonged sleep may be a precursor to Alzheimer’s disease, according to a study that tracked older people‘s daytime sleep habits.
The results of the study may help resolve conflicting findings about the effects of long-term sleep on cognitive performance in older adults. Some previous research has highlighted the benefits of daytime naps for mood, alertness, and mental task performance.
The latest study suggests that increasing the amount of sleep over time was associated with a higher likelihood of developing mild cognitive impairment or Alzheimer’s disease.
Scientists consider it more likely that excessive sleep may be an early warning signal rather than a cause of mental decline.
“This could be a signal of accelerated aging,” said Dr. Yue Leng, assistant professor of psychiatry at the University of California, San Francisco. “Key takeaway: If you haven’t napped before and notice that you’re getting more daytime sleep, this could be a sign of worsening cognitive health.”
The scientists followed more than 1,000 people, with an average age of 81, for several years. Each year, participants wore a watch-like device to track movement for 14 days. Every long period of inactivity from 9 am to 7 pm was regarded as sleep.
Participants also took annual cognitive assessment tests. At baseline, 76% of participants had no cognitive impairment, 20% had mild cognitive impairment, and 4% had Alzheimer’s disease.
In participants who did not develop cognitive impairment, daily daytime sleep increased by an average of 11 minutes per year.
According to a study published in the journal Alzheimer’s and dementia, after a diagnosis of mild cognitive impairment, this figure doubled to 24 minutes, and after a diagnosis of Alzheimer’s disease, it almost tripled, to 68 minutes.
Overall, participants who napped for more than an hour a day had a 40% higher risk of developing Alzheimer’s disease than those who napped for less than an hour a day; and participants who napped at least once a day had a 40% higher risk of developing Alzheimer’s disease than those who napped less than once a day.
Previous studies comparing post-mortem brain scans found that people with Alzheimer’s disease had fewer specialized neurons that promote wakefulness.
Bizarre sleep patterns, insomnia, and poor nighttime sleep quality are common among people with dementia, but recent work has shown that the association with snoozing persists even when nighttime sleep is accounted for. “This suggests that the role of daytime sleep is important in its own right,” Leng said.
According to the authors, feeling increasingly sleepy during the day may be an early sign that changes are taking place in the brain that are harbingers of dementia.
Leng said the possibility that naps cause cognitive problems cannot be ruled out, but “there is no apparent biological mechanism by which naps could cause Alzheimer’s.”
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