Taking regular naps during the daytime is associated with better brain health in adults aged between 40 and 69.
This is the conclusion of a study by researchers from University College London, which found a link between habitual napping and having a larger total brain volume.
This, the team explained, is a marker of good brain health that is in turn linked to a lower risk of dementia and other forms of cognitive decline.
The findings build on the results of previous studies that have shown that napping offers cognitive benefits — boosting performance in tests in the hours after a quick kip.
Previous research has estimated that, in the UK, nearly a third of adults aged 65 or over have a regular nap during the daytime.
The study was undertaken by neuroscientist Valentina Paz of the University of the Republic in Uruguay, genetic epidemiologist Dr Victoria Garfield of University College London and geneticist Dr Hassan Dashti of the Massachusetts General Hospital.
Dr Garfiled said: “Our findings suggest that, for some people, short daytime naps may be a part of the puzzle that could help preserve the health of the brain as we get older.”
In their investigation, the trio analyzed cognitive, genetic and health data on 378,932 adults aged 40–69 — and with a mean age of 57 — sourced from the UK Biobank.
This is a large-scale database containing detailed health and genetic information on a total of some half-a-million participants.
In particular, the team focussed on 92 genetic variants previously identified by Dr Dashti that have been associated with people’s likelihood of engaging in habitual napping.
The researchers found that those people who were genetically “programmed” to engage in regular napping were more likely to have a larger total brain volume.
Moreover, the average difference in brain volume between habitual nappers and their counterparts was equivalent to having aged between 2.6–6.5 years.
Despite this, however, the team did not find a difference in how nappers vs non-nappers performed in three other measures of brain health and cognitive function — hippocampal volume, reaction time and visual processing.
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Ms Paz said: “This is the first study to attempt to untangle the causal relationship between habitual daytime napping and cognitive and structural brain outcomes.
“By looking at genes set at birth, Mendelian randomisation avoids confounding factors occurring throughout life that may influence associations between napping and health outcomes.
“Our study points to a causal link between habitual napping and larger total brain volume.”
The team did not have information on how long the nappers tended to doze during the day. Previous studies, however, have indicated that naps of 30 minutes or less provide the best short-term benefits, and those taken earlier in the day are less likely to disrupt sleep at night.
The team did caution that the design of their study came with some inherent limitations.
Specifically, all of the participants were of white European ancestry, meaning that the findings may not necessarily extrapolate to other ethnicities.
Dr Garfield concluded: “I hope studies such as this one showing the health benefits of short naps can help to reduce any stigma that still exists around daytime napping.”
The full findings of the study were published in the journal Sleep Health.
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