American scientists found a connection between frequent daytime sleep and an increased risk of developing dementia in people over 65 years old. According to a Johns Hopkins Bloomberg School of Public Health study, people who slept during the day almost every day had a 48% higher relative risk of developing dementia compared to those who hardly practiced daytime sleep.
The results of the study were published in the scientific journal The Journals of Gerontology: Series A. The final version of the article was published on October 5, 2026, and the university released a separate report on the results of the work on October 13.
The study involved 995 Americans aged 65 and older who received health insurance under the Medicare program. At the start of follow-up in 2013, none of the participants had signs of probable or possible dementia according to the classification used by the researchers.
Researchers followed the participants for up to ten years using data from the National Health and Aging Trends Study (NHATS). They analyzed not only the duration of night sleep, but also the frequency of daytime rest, its duration and the circumstances of falling asleep.
Researchers paid special attention to the difference between planned daytime sleep and cases when a person falls asleep involuntarily, for example, while watching TV, reading or resting in a chair.
According to the results of statistical analysis, frequent daytime sleep was associated with an increase in the relative risk of dementia by 48%, and unplanned falling asleep - by 39%.
At the same time, scientists took into account age, sex, education, presence of chronic diseases, body mass index, symptoms of depression and anxiety, as well as characteristics of night sleep and the risk of obstructive sleep apnea.
The relationship remained noticeable even after making these corrections, which indicates the potential independent role of daytime sleep characteristics as an indicator of the risk of cognitive disorders.
Researchers also found that daytime sleep lasting up to 30 minutes was associated with a 40% increase in the relative risk of dementia. At the same time, for sleep lasting more than 30 minutes, the statistical relationship weakened after taking into account the characteristics of night rest.
However, irregular or consciously planned daytime sleep did not show a statistically significant increase in risk after taking into account all the main factors.
In total, during the observation period, 417 participants, or 41.9% of the sample, had signs of possible or probable dementia. Among people who did not sleep during the day, such a result was recorded in 37.8%, and among those who regularly rested during the day - in 51.1%. At the same time, the duration of observation of individual groups differed, so these proportions should not be taken as a direct prediction of individual risk.
Exceptdementia, scientists have found a connection between frequent daytime sleep and further deterioration of memory and certain executive functions of the brain, in particular the ability to plan and control complex actions.
However, the researchers emphasize that the obtained results do not prove a causal relationship between daytime sleep and dementia.
"More frequent daytime sleep may be a sign of changes in the brain, and not the cause of changes that lead to dementia," said the senior author of the study, professor Adam Spear, Department of Mental Health, Johns Hopkins University.
According to the scientists, neurodegenerative processes can begin long before clinical symptoms of dementia appear. The areas of the brain that regulate wakefulness and sleep may be among the first to change. Because of this, a person may fall asleep more often during the day even before the diagnosis is established.
To test this hypothesis, the researchers conducted an additional analysis, excluding cases of dementia detected during the first five years of observation. The connection between frequent daytime sleep and the subsequent development of dementia remained. For unplanned falling asleep, the direction of the relationship also remained similar, but the statistical uncertainty of the result increased.
The first author of the study, Kening Jiang, noted that observing changes in daytime sleep may be a relatively simple way of early detection of people at increased risk of dementia.
Scientists believe that doctors should pay attention not only to patients' complaints about night sleep, but also to an increase in the frequency of daytime sleepiness, especially if such changes occur without an obvious reason.
At the same time, the authors warn against hasty practical conclusions. The study was observational in nature: the scientists did not change the sleep patterns of the participants and did not check whether the refusal of daytime rest could prevent dementia.
In addition, information about daytime sleep was collected mainly from the words of the participants themselves, and the signs of dementia were determined according to a validated algorithm, and not based on the results of clinical diagnosis of each case.
So, the results do not mean that a short daytime sleep in itself harms the brain or that it should be avoided. Instead, new or increasingly frequent involuntary sleepiness in the elderly may be a reason to discuss the state of health, the quality of night sleep and possible cognitive changes with a doctor.
To definitively establish a causal relationship, additional long-term studies with objective measurement of sleep using special devices are needed.
Johns Hopkins University, founded in 1876 in Baltimore, USA, is one of the leading research universities of the USA. His School of Public Health Bloomberg (Johns Hopkins Bloomberg School of Public Health), founded in 1916, specializes in epidemiology, disease prevention, mental health, population aging, and the study of risk factors.chronic diseases. Research on daytime sleep and dementia was conducted with partial financial support from the US National Institute on Aging.
Sources: Johns Hopkins Bloomberg School of Public Health, message dated 13 October 2026; original research in The Journals of Gerontology: Series A, DOI: 10.1093/gerona/glag208.
