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(CNN) -- Napping during the day may help maintain brain health as we age, according to a new study. However, previous research has shown that excessive naps can also be harmful.
The habitual practice of napping was related to a higher total brain volume, which is associated with a lower risk of dementia and other diseases, according to researchers from University College London (UCL) and the University of the Republic of Uruguay.
On average, the difference in brain volume between those who napped and those who did not equated to between 2.5 and 6.5 years of aging, according to the researchers.
"Our findings suggest that, for some people, short daytime naps may be a part of the puzzle that could help preserve brain health as we age," lead author Victoria Garfield, a researcher at UCL, said in a statement.
While the study was "well conducted," its limitations include the fact that napping habits were self-reported, said Tara Spires-Jones, president of the British Neuroscience Association and deputy director of the Centre for Brain Science Discovery at the University of Edinburgh, who was not involved in the study.
The results show "a small but significant increase in brain volume in people who have a genetic signature associated with daytime napping," he told the Science Media Centre.
"Even with those limitations, this study is interesting because it adds to the data indicating that sleep is important for brain health," he said.
In response, the study's lead author, Valentina Paz, a researcher at the University of the Republic of Uruguay and UCL, told CNN that she agreed that "the work has some limitations," but that they are "confident" about the method used in the study.
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In the study, published Monday in the academic journal Sleep Health, researchers used a technique called Mendelian randomization to analyze DNA samples and brain scans from 35,080 people aged 40 to 69 who took part in the UK Biobank study, a large biomedical database and research resource that followed U.K. residents between 2006 and 2010.
Mendelian randomization is a statistical approach that uses genetics to provide information about the relationship between an exposure and an outcome.
The researchers analyzed sections of the genetic code linked to the likelihood that people napped regularly, and then compared brain health and cognition outcomes between those who had the napping genes and those who did not.
"By analyzing genes fixed at birth, Mendelian randomization avoids confounding factors that occur throughout life and that may influence associations between napping and health outcomes," said Paz, lead author, in the statement.
The study looked at more than 35,000 people between the ages of 40 and 69. Credit: MoMo Productions/Digital Vision/Getty Images
However, such a technique can only show an association between napping and brain health, not cause and effect. In addition, the researchers had no information on nap length, which can influence whether sleep is helpful or harmful.
Paz told CNN that previous findings suggest that "taking a short nap (5 to 15 minutes) in the early afternoon may benefit those in need."
- Excessive Naps May Be an Early Sign of Dementia, New Study Finds
Napping can also be harmful
Meanwhile, previous research has shown that napping frequently or for prolonged periods throughout the day can be a sign of early dementia in older adults.
Older adults who napped at least once a day or more than an hour a day were 40% more likely to develop Alzheimer's than those who didn't nap daily or napped less than an hour a day, according to a study published in Alzheimer's and Dementia: The Journal of the Alzheimer's Association, in March 2022.
And in July 2022, a study found that people who nap frequently are more likely to develop high blood pressure and suffer a stroke or stroke.
Study participants who regularly napped during the day were 12% more likely to develop hypertension over time and 24% more likely to have a stroke, compared to people who never napped.
"This may be because while napping itself is not harmful, many people do so because they sleep poorly at night. Poor sleep at night is associated with poorer health, and naps are not enough to compensate," clinical psychologist Michael Grandner said in a statement at the time. Grandner directs the Behavioral Sleep Medicine Clinic at Banner-University Medical Center in Tucson, Arizona, and was not involved in the study.
- Regular Napping Linked to Higher Risk of High Blood Pressure and Stroke, Study Finds
Excessive naps can be a sign of an underlying sleep disorder, Dr. Raj Dasgupta, a sleep specialist and associate professor of clinical medicine at the University of Southern California's Keck School of Medicine, told CNN in an earlier interview.
"Sleep disorders are linked to increased stress and weight-regulating hormones, which can lead to obesity, high blood pressure and type 2 diabetes, all risk factors for heart disease," he said. "I think napping is a warning sign of an underlying sleep disorder in certain individuals."