Taking longer or more frequent naps during the day may sound enticing, but it may be a harbinger of Alzheimer's disease.
Older adults who nap throughout the day may be more likely to develop Alzheimer's, while napping may also be a consequence of advancing Alzheimer's, a new study suggests.
"Daytime napping and Alzheimer's disease seem to be driving each other's changes in a bi-directional way," said study author Dr. Yue Leng. She is an assistant professor of psychiatry at the University of California, San Francisco.
The bottom line? "Older adults, and especially those with Alzheimer's disease, should pay more attention to their daytime napping behaviors," Leng said.
There are several potential ways that daytime napping and Alzheimer's may be linked.
"It could be a reflection of underlying Alzheimer's pathology at the preclinical stage that affects the wake-promoting network and contributes to increased daytime sleepiness," she said. "Excessive daytime napping might also impact and interact with nighttime sleep, resulting in altered 24-hour circadian rhythms, which has also been linked to an increased risk of Alzheimer's."
For the study, more than 1,400 older Americans, average age 81, wore a watch-like activity monitor for two weeks every year. Any prolonged period of no activity from 9 a.m. to 7 p.m. was considered a nap. Participants also underwent a battery of neurological tests each year.
When the study started, more than three-quarters of participants showed no signs of any cognitive impairment, 19.5% had mild cognitive impairment, and slightly more than 4% had Alzheimer's disease.
Daily napping increased by about 11 minutes per year among folks who didn't develop cognitive impairment during roughly 14 years of follow-up. The greater the increase in naps, the more quickly memory and thinking skills declined, the findings showed.
The rate of increase in naps doubled after a diagnosis of mild cognitive impairment and nearly tripled after a diagnosis of Alzheimer's disease, according to the report published March 17 in the journal Alzheimer's & Dementia.
Another part of the study sought to determine if napping is a risk for developing Alzheimer's disease. To answer this question, the researchers compared participants who had normal memories and thinking skills at the start of the study but developed Alzheimer's disease to their counterparts whose thinking remained stable during the study. They found that older people who napped more than an hour a day had a 40% higher risk of developing Alzheimer's.
Alzheimer's disease affects more than just memory and thinking skills, said study author Dr. Aron Buchman. He's a professor of neurology at Rush University Medical Center and a neurologist at Rush Alzheimer's Disease Center, in Chicago.
In some, this disease may steal memories, but in others, it may result in sleep issues. In others, it could affect motor function, Buchman said.
"More studies are needed to better understand the relationship between napping and Alzheimer's disease. But it's possible that improving sleep may be a way of modifying the course of Alzheimer's disease and its manifold manifestations," he added.
Experts who were not involved with the study caution that it is way too early to say napping increases the risk for Alzheimer's disease.
Study patients could have already had pre-clinical signs of Alzheimer's disease in their brains, said Ricardo Osorio, director of the Center for Sleep and Brain Health at NYU Langone in New York City. "At age 80, even with no symptoms, it is quite common to have Alzheimer's pathology in the brain," he explained.
In the future, research should look at napping patterns in younger people and follow them to see who develops Alzheimer's disease and who doesn't, Osorio suggested.
People can nap for reasons that have nothing to do with Alzheimer's disease, he said. Daytime naps may be a result of sleep apnea, overexertion during the day, or even depression and loneliness. "We need to tease out the other things that may cause people to nap more before drawing conclusions," Osorio added.
There are other caveats as well, said Dr. Derek Chong, vice chair of neurology at Lenox Hill Hospital in New York City.
"This study was performed in Chicago, where the society tends to have only one sleep period at night," Chong said. "Many other cultures and societies have a siesta or midday nap that is often longer than one hour long, and some of these cultures are known to have slow aging, so these results may not be applicable worldwide."
Still, this study does call attention to the health consequences of poor sleep, he noted.
"Even though the study does not tell us the cause for why people need to nap more, it should remind us the importance of daytime stimulation, seeking help with depression, and high-quality sleep, and checking with your doctor for things like sleep apnea, especially when we are sleepy during the day," Chong said.