Daytime naps in older adults are normal in the aging process, but it may also signal Alzheimer’s and other dementias.
The frequency and/or duration of napping in older adults increases rapidly once dementia or its common precursor (mild cognitive impairment) is diagnosed, according to a new study.
The study was conducted by the University of California, San Francisco (UCSF), Harvard Medical School, Brigham and Women’s Hospital.
Research suggests that dementia may affect wake-promoting neurons in key areas of the brain. This contradicts the theory that older adults take daytime naps only to compensate for lack of sleep at night.
The study was published March 17 in Alzheimer’s and Dementia.
Gallery copyright pictures, unauthorized reproduction
“After adjusting for the quantity and quality of nighttime sleep, we found that the association between excessive daytime napping and dementia persisted,” said co-author Yue Leng of UCSF’s Department of Psychiatry and Behavioral Sciences.
For the study, researchers tracked data from 1,401 older adults who were 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, about three-quarters were women, wore a watch-like device to track their movements. Every extended period of inactivity, from 9 a.m. to 7 p.m., was defined as a nap.
Each participant wore the device for 14 consecutive days per year and underwent an annual neuropsychological test to assess cognitive performance.
At the start of the study, 75.7% of 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 naps increased by an average of 11 minutes per year.
After being diagnosed with mild cognitive impairment, this time reached 24 minutes; after being diagnosed with Alzheimer’s disease, this time reached 68 minutes.
Gallery copyright pictures, unauthorized reproduction
The researchers looked at 24 percent of the participants.
They were cognitively normal at the start of the study, but developed Alzheimer’s six years later.
The researchers compared them with those whose cognitive abilities remained stable and found differences in nap habits.
Participants who napped for more than an hour a day had a 40% higher risk of developing Alzheimer’s disease than those who napped less than an hour a day; those who napped at least once a day had a higher risk of developing Alzheimer’s disease than those who napped less than once a day 40% higher risk of developing Alzheimer’s.
The finding confirms the findings of a 2019 study by Leng that older adults who took a two-hour nap a day were more likely to develop cognitive impairment than those who took a nap of less than 30 minutes a day.
A study by other UCSF researchers could explain the increase in napping, researchers say.
The study compared the postmortem brains of Alzheimer’s patients with those without cognitive impairment and found wake-promoting neurons in three regions of the brains of people with Alzheimer’s less.
These neuronal changes appear to be related to tau tangles — a hallmark of Alzheimer’s disease characterized by increased activity of enzymes that cause proteins to misfold and clump together.
“I don’t think we have enough evidence to draw a causal conclusion that napping itself causes cognitive decline, but excessive daytime napping may be a signal of accelerated aging or cognitive decline.”
Leng said, “Future studies will be very interesting to explore whether napping interventions can help slow age-related cognitive decline.”