PUMPING IRONY: The Big Sleep

On the first day of his retirement earlier this year, an old pal of mine enjoyed not one, but two luxurious naps. He did not tell me whether he had been sleep-deprived due to excessive celebrating during the previous evening or if he simply chose to snooze because, well, he could. Whatever it was that lured him to the couch, he’s in good company: A 2020 study found that as many as 60 percent of older U.S. adults nap on a regular basis.

But, despite its restorative properties, daytime slumber has earned a mixed reputation among the scientific community. It’s a perfectly healthy habit for seniors, research has shown — except when it’s not.

Researchers at Massachusetts General Hospital, for instance, presented a study at last month’s annual meeting of the American Academy of Sleep Medicine that suggests certain napping habits may increase a senior’s mortality risk. Some of the results were surprising, notes lead study author Chenlu Gao, PhD.

Gao’s team analyzed the napping patterns of more than 86,000 older adults who wore sleep monitors for seven days. Researchers then tracked mortality data from that cohort over the next 11 years and detected some novel connections.

“In evaluating the results of the sleep study, we were surprised by how common napping was among middle- to older-aged adults, how much their daytime sleep patterns varied across days, and when during the day they are sleeping,” Gao explains. “People who slept longer during the day, had irregular daytime sleep patterns, or slept more around midday and early afternoon were at greater risk, even after accounting for health and lifestyle factors.”

The mortality risks of midday napping had not clearly emerged from previous studies, which have often suggested a more salutary link between daytime shuteye and cognitive function. A 2020 study, for example, noted increased activation in the brain’s hippocampus (a key to memory) among nappers, and a 2023 report suggested napping could even expand the size of a senior’s brain.

In a more wide-ranging review, Michael Chee, MBBS, and his team of researchers at the National University of Singapore found that 30-minute naps produced improvements in two specific cognitive functions: memory encoding and sustained concentration. “While there is no clear ‘winning’ nap duration, a 30-minute nap appears to have the best tradeoff between practicality and benefit,” he writes in the journal Sleep.

Longer naps, in fact, may be a sign of cognitive dysfunction, says Yue Leng, PhD, an associate professor in the Department of Psychiatry at the University of California, San Francisco (UCSF).

Leng led a 2022 study that revealed a troubling connection between nap duration and dementia. Among participants displaying no cognitive dysfunction at the beginning of the study, those who napped more than an hour a day were 40 percent more likely than those who snoozed for less than an hour to develop Alzheimer’s during a six-year follow-up period.

“This is an association, so we can’t say if it’s napping itself that causes the increased risk,” Leng tells the San Francisco Chronicle. “It could be that increased daytime sleepiness is an early marker of dementia, which means before they develop cognitive symptoms, maybe they’re already having declining cognition or health that makes them more sleepy overall.”

Leng’s colleagues at UCSF explained why that might be the case in a 2019 report, in which they noted that a lack of “wake-promoting” neurons — linked to dementia-promoting tau tangles in the brain — may keep some people napping longer than others. If that’s the case, we may not have much control over our daytime slumber as we grow older. And, at a certain point, it may be the least of our worries. If we’re caught in the grip of Alzheimer’s, after all, a long midday snooze may be more of a blessing than a curse.

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