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Older Americans who napped most days were more likely to develop dementia than those who rarely napped. In a Johns Hopkins study of 995 Medicare beneficiaries, frequent nappers had a 48% higher risk, even after accounting for health and nighttime sleep.
That does not mean naps damage the brain. One of the study’s senior authors thinks the nap is more likely a signal of changes already under way. About one in five people in the study napped most days. For them, the finding is a reason to notice daytime sleepiness, not to give up the afternoon nap.
What the Hopkins team measured
The paper, “Napping characteristics and incident dementia,” appeared online on October 5 in The Journals of Gerontology: Medical Sciences. The Johns Hopkins Bloomberg School of Public Health announced it on October 13. Kening Jiang, a postdoctoral fellow, is first author.
The data come from the National Health and Aging Trends Study, a nationally representative survey. It has interviewed Medicare beneficiaries aged 65 and older every year since 2011. In 2013, a subset answered extra questions about how often they napped, whether the naps were planned and how long they lasted.
The researchers kept 995 people who were free of dementia in 2013 and followed them through 2023. Over a median of five years, 417 of them (41.9%) met the survey’s definition of possible or probable dementia.
That definition matters. The survey does not rely on a doctor’s diagnosis. It flags dementia with an algorithm built on reported diagnoses, a family member’s questionnaire and three short cognitive tests. A low score in just one of those three tests counts as “possible” dementia.
What 48%, 39% and 40% actually mean
All three headline numbers are hazard ratios. Each one compares a group of nappers with the 482 people who said they “never” or “rarely” napped. A hazard ratio of 1.48 means new dementia cases appeared at a rate about 48% higher. It does not mean 48% of nappers got dementia.
The paper’s raw counts give a plainer picture. Among non-nappers, 37.8% developed possible or probable dementia during the study. Among people who napped most days or every day, 51.1% did.
The researchers adjusted for age, sex, race, education, smoking, weight, chronic illness, and depression and anxiety symptoms. They also adjusted for nighttime sleep length, daytime sleepiness and sleep apnea risk. After all that, here is what each figure refers to:
- Frequent napping (48%): napping “most days” or “every day,” reported by 221 people. Napping on “some days” showed no clear link.
- Unintentional napping (39%): falling asleep without meaning to, or a mix of planned and unplanned naps. Planned naps alone showed no clear link once health was considered.
- Short naps (40%): naps of 30 minutes or less. Longer naps showed a link at first, but it lost statistical significance once nighttime sleep was added.
That last result surprises people, since sleep experts usually recommend short naps. The authors suggest that long naps mostly make up for bad nights. Adjusting for nighttime sleep would then absorb their effect. The short-nap finding also turned out to be the least sturdy.
Why the researchers think naps may be a symptom
The obvious problem with any napping study is reverse causation. Dementia can damage the brain regions that keep people awake, and the Hopkins release says this can happen early. So a brain in the early stages of dementia could produce the naps, not the other way round.
“More frequent napping could be a marker of changes in the brain, rather than a cause of brain changes that lead to dementia,” said Adam Spira in the release. He is a professor in the Bloomberg School’s Department of Mental Health and one of the paper’s two senior authors.
To test this, the team dropped every dementia case that appeared in the first five years. The link with frequent napping held up and even grew, to a hazard ratio of 1.75.
The release says the unintentional-napping link “remained similar.” The estimate did stay at 1.40. But the paper reports a confidence interval of 0.95 to 2.06, a range that includes no effect at all. The short-nap link weakened to 1.24 and was no longer statistically significant.
A second check pointed the same way. Counting only probable dementia, the more severe category, frequent napping still predicted it. Unintentional napping and short naps did not.
So the strongest signal is the simplest one. Napping most days, reported once in 2013, predicted dementia years later. The finer points about intention and nap length are much shakier.
What the study can’t rule out
Other limits are spelled out in the paper. The authors note that napping was self-reported in a single interview, which invites recall errors. Their tables show frequent nappers were also heavier and had more chronic illness, depressive symptoms and daytime sleepiness. Statistics can only adjust for what researchers measured.
The paper’s disclosures also list consulting work for sleep and pharmaceutical companies by several authors, including Spira and Kaufmann.
The authors also chose not to correct for running many comparisons, which raises the odds that some findings are flukes.
What earlier napping studies found
This is not the first study to tie heavy napping to dementia. In March 2022, researchers led by UC San Francisco and Harvard Medical School studied 1,401 older adults in Chicago. The participants, from the Rush Memory and Aging Project, wore activity trackers that measured naps directly. The team followed them for up to 14 years.
People who napped more than an hour a day had a 40% higher risk of Alzheimer’s than those who napped less, according to UCSF’s release. Naps and the disease “seem to be driving each other’s changes in a bi-directional way,” co-senior author Yue Leng said. The paper’s abstract says an Alzheimer’s diagnosis more than doubled the yearly increase in napping.
Not every study agrees. The Hopkins paper notes that the UK’s Million Women Study, of more than 830,000 women, found no link with self-reported napping. A Japanese study of 389 older adults tied naps under 30 minutes to less cognitive decline.
The most upbeat result came from the UK Biobank. In 2023, University College London researchers used genetics to study 378,932 people aged 40 to 69. Those whose DNA made them likelier to nap habitually had larger total brain volumes. The gap equalled 2.6 to 6.5 years of brain aging, according to UCL’s release.
That study measured brain size in middle-aged adults, not dementia in older ones. It found no difference in the hippocampus, a memory region, or in reaction time. It also had no data on nap length.
Much of this field eventually depends on brain tissue donated for dementia research, which shows what was happening inside the brain. And aging is not a straight line down, as a study on mental sharpness into the 90s found.
Should you stop napping?
Nothing in the paper or the release tells readers to stop napping. The authors write that napping “may be a modifiable risk factor for dementia if supported by further evidence.” Nobody has yet tested whether cutting back on naps changes anyone’s risk.
Their more practical point is about noticing change. Monitoring naps “could serve as an early and accessible marker” of higher dementia risk, Jiang said in the release. Frequent, unplanned dozing is the pattern this study flagged.
The National Institute on Aging’s guidance on sleep says older people still need seven to nine hours a night. It advises against napping in the late afternoon or evening. Anyone who is “always sleepy” or struggles to sleep at night should talk with a doctor, the agency says. The Hopkins paper notes that problems such as sleep apnea can cause daytime sleepiness and naps.
The Hopkins team wants longer studies that measure naps and nighttime sleep objectively, rather than relying on memory. Only that evidence, the researchers say, can show whether changing napping habits could delay or prevent dementia.