The elderly love to take naps, that may not be due to sleepiness

Daytime napping in older adults is normal in the aging process, but it can also be a sign of Alzheimer's and other dementias.

Once diagnosed with dementia or its common precursor, mild cognitive impairment, older adults rapidly increase the frequency and/or duration of naps, according to a new study.

The study was conducted jointly by the University of California, San Francisco (UCSF), Harvard Medical School, and Brigham and Women's Hospital.

Dementia may affect wakefulness-promoting neurons in a key area of the brain, the study suggests, contradicting the theory that older people take daytime naps simply to make up for lost sleep at night.

The related research was published in Alzheimer's & Dementia on March 17.

"After adjusting for the quantity and quality of nighttime sleep, we found that the association between excessive daytime napping and dementia remained," said co-author Yue Leng of the UCSF Department of Psychiatry and Behavioral Sciences.

For the study, researchers tracked data from 1,401 older adults who had been followed for 14 years by the Rush Memory and Aging Project at the Rush Alzheimer's Center in Chicago.

The participants, whose average age was 81 and about three-quarters were women, wore a watch-like device that tracked their movements, with each long period of inactivity between 9 a.m. and 7 p.m. defined as a nap.

Each participant wore the device continuously for 14 days per year and underwent annual neuropsychological testing to assess cognitive abilities.

At the start of the study, 75.7% of the participants had no cognitive impairment, while 19.5% had mild cognitive impairment and 4.1% had Alzheimer's disease.

For participants without cognitive impairment, daytime napping increased by an average of 11 minutes per year.

After being diagnosed with mild cognitive impairment, that time rose to 24 minutes; after being diagnosed with Alzheimer's, that time rose to 68 minutes.

The researchers looked at 24 percent of the participants.

They had normal cognitive abilities at the start of the study but developed Alzheimer's disease six years later.

The researchers compared them with people whose cognitive abilities remained stable and found differences in their napping habits.

Participants who napped for more than an hour a day had a 40% higher risk of developing Alzheimer's disease compared to those who napped less than an hour a day; participants who napped at least once a day had a 40% higher risk of developing Alzheimer's disease compared to those who napped less than once a day.

This finding confirms the results of a 2019 study conducted by Leng, which showed that older adults who napped for two hours a day had a higher incidence of cognitive impairment than those who napped for less than 30 minutes a day.

The researchers say a study by other UCSF researchers could explain the increase in napping.

The study compared postmortem brains of people with Alzheimer's with those without cognitive impairment and found that people with Alzheimer's had fewer wakefulness-promoting neurons in three areas of the brain.

These neuronal changes appeared to be linked to tau tangles — a hallmark of Alzheimer's disease characterized by increased activity of enzymes that cause proteins to misfold and clump.

“I don’t think we have enough evidence to draw a causal conclusion that napping itself causes cognitive decline, but excessive napping during the day could be a sign of accelerated aging or cognitive decline.”

"It would be very interesting to conduct future studies to explore whether napping interventions could help slow down age-related cognitive decline," Leng said.

Source: China Science Daily

Author: Wen Lele