A recent study suggests that napping during the day can reduce the rate at which our brains shrink as we age by preserving brain health.

The study, led by researchers at UCL and the University of the Republic in Uruguay, used data from people between the ages of 40 and 69.

They found an association between regular napping and having a larger total brain volume, which is an indication of good health and is linked to a decreased risk of developing diseases such as dementia.

Senior author, Dr Victoria Garfield from the MRC Unit for Lifelong Health & Ageing at UCL, 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.”

Research has previously suggested that napping has cognitive benefits. It found that people who had a short nap in the hours before completing a cognitive test performed better compared to those who did not nap.

The new study sought to determine whether there is a link between napping during the day and good brain health.

The researchers analysed 97 fragments of DNA using Mendelian randomisation to establish someone’s likelihood of napping regularly.

Using the data of 378,932 people from the UK Biobank study, they found that those who were genetically “programmed” to nap had a greater brain volume.

They discovered that the average brain volume in those predetermined to nap compared to those who were not was equivalent to 2.6 to 6.5 years of aging.

However, the researchers found no difference in hippocampal volume, reaction time or visual processing (other measures of brain health and cognitive function) for those who napped compared to those who did not.

Valentina Paz, lead author and PhD candidate of the University of the Republic (Uruguay) and MRC Unit for Lifelong Health & Ageing at UCL, explained: “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.”

“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,” added Dr Garfield.

A previous study involving 452,633 participants from the UK Biobank identified the genetic variants which effected our likelihood to nap. Dr Hassan Dashti from Harvard University and Massachusetts General Hospital and the study lead in this previous study and the new study based the study on self-reported napping which was supported by measurements of physical activity from wrist-worn accelerometers.

The new study examined the health and cognition outcomes for the people identified as having these genetic variants and various subsets of these variants that were selected to avoid bias, such as avoiding variants associated to extreme fatigue during the day.

An important factor to consider is that all study participants were of white European ancestry so results may be different for other ethnicities.

Although the researchers of the new study were unaware of nap duration, a past study had already identified that short naps of 30 minutes of less resulted in the best cognitive benefits and that napping early in the day was less likely to impact night-time sleep.

The study was published in the journal Sleep Health.

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