Regular daytime napping could aid brain health by slowing the rate at which brains shrink with ageing, according to a study published today.
The research by UCL, UK, and the University of the Republic, Uruguay found a causal link between habitual napping and larger total brain volume, which is a marker of good brain health linked to a lower risk of dementia and other diseases.
Although previous research has shown that napping has cognitive benefits – with nappers performing better in cognitive tests than others who did not – this new study wanted to establish if there was a causal relationship between daytime napping and brain health.
Using Mendelian randomisation, they analysed data from 378,932 people, aged 40 to 69, from the UK Biobank study, examining 97 snippets of DNA that are believed to determine people’s likelihood of habitual napping.
When they compared measures of brain health and cognition of people who are more genetically “programmed” to nap with individuals who do not have these genetic variants, they found those who were predetermined to nap had a larger total brain volume.
Writing in Sleep Health, they found the average difference in brain volume between people programmed to be habitual nappers and those who were not was equivalent to 2.6 to 6.5 years of ageing.
Lead author and PhD candidate Valentina Paz, from the University of the Republic and the MRC Unit for Lifelong Health & Ageing at UCL, 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 teams analysed health and cognition outcomes for people with these genetic variants as well as several different subsets of these variants, adjusted to avoid potential bias, such as avoiding variants linked to excessive daytime sleepiness.
Genetic data and magnetic resonance imaging (MRI) scans of the brain were available for 35,080 individuals drawn from the UK Biobank sample.
While the researchers did not have information on nap duration, earlier studies suggest that naps of 30 minutes or less provide the best short-term cognitive benefits, and napping earlier in the day is less likely to disrupt night-time sleep.
Paz V, Dashti HS, Garfield V. Is there an association between daytime napping, cognitive function and brain volume? A Mendelian randomisation study in the UK Biobank. Sleep Health 20 June 2023; doi: 10.1016/j.sleh.2023.05.002
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