Our brains – like our muscles – shrink with age. Exercise is one way to slow the decline in both brain and body.

And day-time naps may aid an ageing brain.

A new study has found “a causal link between habitual napping and larger total brain volume”.

Larger brain volume is “a marker of good brain health linked to a lower risk of dementia and other diseases”.

Senior author of the new paper, Dr Victoria Garfield of the University College London, 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.”

Interesting study design

How did they get these findings? Some researchers would gather self-reported data on napping habits from participants over a number of years. And then, during that period, measure brain volumes using MRI.

The new study, using a technique called Mendelian randomisation, took a different route to their findings.

They began with the idea that some people are more genetically programmed to take regular naps than others.

The researchers analysed data from 378,932 people from the UK Biobank. These were people aged 40 to 69.

From this data bank, researchers analysed 97 snippets of DNA “thought to determine people’s likelihood of habitual napping”.

The researchers determined who was genetically predisposed to napping, and who wasn’t. Then, using MRI scans from the UK Biobank, their brain volumes were compared.

The findings

Overall, participants who were predetermined to nap had a larger total brain volume.

The researchers estimated that “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”.

However, the researchers didn’t find a difference in “how well those programmed to be habitual nappers performed on three other measures of brain health and cognitive function – hippocampal volume, reaction time and visual processing”.

Lead author and PhD candidate Valentina 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.”

Good naps, bad naps

As the researchers note, previous research has shown that napping has cognitive real-life benefits.

For example, people who’ve had “a short nap perform better in cognitive tests in the hours afterwards than counterparts who did not nap”.

Here’s a sample of the research:

A 2015 study from the University of Sheffield study found that napping helps infants develop their memory and retain new behaviours they have learnt.

A 2015 study from University Saarland found that a short nap lasting about an hour can significantly improve memory performance.

A 2019 report from the American College of Cardiology found that a midday nap was linked to healthy drops in blood pressure akin to those gained from exercise and other lifestyle changes. Which is good for the brain.

A 2021 report found that for people aged 60 and over, a regular afternoon nap was linked to better mental agility. Specifically, napping was “associated with better locational awareness, verbal fluency, and working memory”.

Some research, though. suggests napping too much isn’t good for you. A 2010 report from the American Academy of Sleep Medicine found that frequent napping was linked to an increased risk of type 2 diabetes and impaired fasting glucose in older adults.

There have been similar studies linking excessive napping with poor cardiovascular health.

My reading of these studies is that it’s not the naps that are the problem. It’s more a general lack of physical activity that does the damage. And, of course, poor heart health tends to leave people exhausted.