Investigators at University College London, and the University of the Republic of Uruguay, Montevideo, found individuals genetically predisposed to regular napping had larger total brain volume, a surrogate of better cognitive health.
“Our results suggest that napping may improve brain health,” first author Valentina Paz, MSc, a PhD candidate at the University of the Republic of Uruguay said in an interview. “Specifically, our work revealed a 15.8 cubic cm increase in total brain volume with more frequent daytime napping,” she said.
The findings were published online in Sleep Health.
Higher brain volume
Previous studies examining the potential link between napping and cognition in older adults have yielded conflicting results.
To clarify this association, Ms. Paz and colleagues used Mendelian randomization to study DNA samples, cognitive outcomes, and functional magnetic resonance imaging data in participants from the ongoing UK Biobank Study.
Starting with data from 378,932 study participants (mean age 57), investigators compared measures of brain health and cognition of those who are more genetically programmed to nap with people who did not have these genetic variations.
More specifically, the investigators examined 97 sections of genetic code previously linked to the likelihood of regular napping and correlated these results with fMRI and cognitive outcomes between those genetically predisposed to take regular naps and those who weren’t.
Study outcomes included total brain volume, hippocampal volume, reaction time, and visual memory.
The final study sample included 35,080 with neuroimaging, cognitive assessment, and genotype data.
The researchers estimated that the average difference in brain volume between individuals genetically programmed to be habitual nappers and those who were not was equivalent to 15.8 cubic cm, or 2.6-6.5 years of aging.
However, there was no difference in the other three outcomes – hippocampal volume, reaction time, and visual processing – between the two study groups.
Since investigators did not have information on the length of time participants napped, Ms. Paz suggested that “taking a short nap in the early afternoon may help cognition in those needing it.”
However, she added, the study’s findings need to be replicated before any firm conclusions can be made.
“More work is needed to examine the associations between napping and cognition, and the replication of these findings using other datasets and methods,” she said.
The investigators note that the study’s findings augment the knowledge of the “impact of habitual daytime napping on brain health, which is essential to understanding cognitive impairment in the aging population. The lack of evidence for an association between napping and hippocampal volume and cognitive outcomes (for example, alertness) may be affected by habitual daytime napping and should be studied in the future.”
Strengths, limitations
Tara Spires-Jones, PhD, president of the British Neuroscience Association and group leader at the UK Dementia Research Institute, said, “the study shows a small but significant increase in brain volume in people who have a genetic signature associated with taking daytime naps.”
Dr. Spires-Jones, who was not involved in the research, noted that while the study is well-conducted, it has limitations. Because Mendelian randomization uses a genetic signature, she noted, outcomes depend on the accuracy of the signature.
“The napping habits of UK Biobank participants were self-reported, which might not be entirely accurate, and the ‘napping’ signature overlapped substantially with the signature for cognitive outcomes in the study, which makes the causal link weaker,” she said.
“Even with those limitations, this study is interesting because it adds to the data indicating that sleep is important for brain health,” said Dr. Spires-Jones.
The study was supported by Diabetes UK, the British Heart Foundation, and the Diabetes Research and Wellness Foundation. In Uruguay, it was supported by Programa de Desarrollo de las Ciencias Básicas, Agencia Nacional de Investigación e Innovación, Comisión Sectorial de Investigación Científica, and Comisión Académica de Posgrado. In the United States it was supported by the National Heart, Lung, and Blood Institute. There were no disclosures reported.
A version of this article first appeared on Medscape.com.