The Links Between Napping And Dementia May Go Further Than We Realized

Dozing off in your armchair in the middle of the afternoon is one of life's simple pleasures.

But depending on how often you find yourself doing it, those daytime naps could be a warning sign of worsening cognitive health, research suggests.

In a new study, researchers found seniors who napped frequently were significantly more likely to develop dementia over the next decade, compared to people who rarely or never napped.

The findings, published in The Journals of Gerontology, Series A: Biological Sciences and Medical Sciences, don't mean that napping is driving cognitive decline, but they identify napping as a risk factor for dementia that we should pay more attention to.

"More frequent napping could be a marker of changes in the brain, rather than a cause of brain changes that lead to dementia," says psychologist and sleep researcher Adam Spira from Johns Hopkins University.

In their study, Spira and fellow researchers analyzed data from the National Health and Aging Trends Study (NHATS), a longitudinal survey of Medicare beneficiaries in the US aged 65 years and older.

The team examined data from 995 of the NHATS participants, all of whom answered questions about their napping habits as part of the research, and none of whom had probable or possible dementia at the outset of the study.

Over a median follow-up period of five years, 417 (41.9 percent) of the participants were classified as having developed possible or probable dementia since the commencement of the study.

After adjusting for a range of potential confounding factors in the data – including age, sex, race/ethnicity, education, smoking status, body mass index, and various health conditions and sleep factors – the researchers found that frequent nappers had the highest risk of developing the condition, compared to infrequent nappers and non-nappers.

Frequent nappers – people who said they napped every day or most days – had a 48 percent higher rate of dementia than people who never or rarely had naps.

Unintentional napping was also associated with a greater risk of dementia (39 percent higher rate than non-nappers).

Length of naps was also a factor, with people who napped for 30 minutes or less having a 40 percent higher rate of dementia than non-nappers in the study period.

Frequent, unintentional, and shorter (30 minutes or less) napping were also found to be associated with higher risks of developing impairment in memory during follow up, the researchers found.

It's worth noting the researchers also found signs of elevated dementia risk associated with infrequent napping, intentional napping, and napping for periods of 30 minutes or longer, but the effects were not statistically significant after adjustment in the final analysis.

Other studies have previously explored the relationship between napping and cognitive health in older adults, but the results have been mixed, with some studies showing signs of elevated cognitive risks associated with napping, and others finding little evidence of a link.

Due to the observational nature of the new study, the findings can't be interpreted as evidence that frequent, unintentional, or short naps cause dementia, and the researchers acknowledge that the links they've found are complicated.

"As with sleep disturbances, the association between napping and dementia may be bidirectional," they write in their paper, "such that neurological changes that adversely affect cognitive function may also lead to increased daytime napping."

In other words, if older adults start to nap a lot during the day, it could be a sign of worsening brain health – but that worsening brain health might also be making them sleepier, prompting them to doze in waking hours.

Another complicating factor is that daytime napping may be a compensatory mechanism, making up for sleep disturbances at night. But just as poor rest at night might induce catch-up napping in the daytime, so might napping disrupt nighttime sleep.

In the study, the researchers accounted for this by adjusting for other sleep-related factors (nighttime sleep duration, daytime sleepiness, and sleep apnea risk), and the results suggest that frequent napping, unintentional napping, and naps lasting 30 minutes or less remain significantly associated with an increased risk of dementia, even after accounting for these other sleep characteristics.

The researchers call for future studies to "disentangle" the possible bidirectionality of the napping-dementia association they've demonstrated here.

While we don't fully understand the nature of this link, the hope is that new research might be able to solve the puzzle, which could lead to new ways to combat dementia, a disease projected to double in the US by 2060.

"Daytime napping might be another modifiable risk factor to be targeted among older adults for primary prevention of dementia, if supported by further causal evidence," the researchers write.

"Even if this association is not causal, napping may be a useful marker of future dementia risk to guide subsequent prevention studies among high-risk populations."

The findings are reported in The Journals of Gerontology, Series A: Biological Sciences and Medical Sciences.