Napping is linked to a larger brain. Does it matter?

Recent headlines blared that regular napping can build a bigger brain and slow neural aging, but don’t feel compelled to schedule a daily siesta just yet. The research that caused the outpouring of media coverage was published in June in the journal Sleep Health. To explore whether napping is beneficial to brain health over the long term, the study authors tapped into the immense UK Biobank, a database of in-depth genetic and health information from half a million residents of the United Kingdom.

The researchers utilized a technique called Mendelian randomization. Thanks to the deluge of data in the UK Biobank, they were able to link numerous gene variants to a greater likelihood of napping in 378,932 subjects (all of whom were aged 40 to 69). The likelihood of napping was gauged based on how subjects replied to the question, “Do you have a nap during the day?” The options were “never or rarely,” “sometimes,” and “usually.”

Genetic influences

They then checked whether the napping-linked gene variants were associated with differences in brain size in a group of 35,080 subjects for which they also had brain scan data. This Mendelian approach helps to account for confounding variables, which can plague epidemiological research.

“These genetic influences are not affected by anything else you may or may not choose to do in your life,” George Davey Smith, a professor of clinical epidemiology at the University of Bristol explained. “We can use this knowledge to learn about cause and effect, grouping people according to their genetic code.”

When it comes to napping, two key variables that can skew data are age and sickness. Older and sicker people tend to nap more often and for longer because they are more fatigued. The researchers found that the people with the gene variants linked to napping had slightly larger brains than people without those gene variants, about 1.3% larger. That might sound small, but the authors of the study noted that it can be quite consequential.

“Our finding of a larger total brain volume in those who habitually nap is approximately equivalent to 2.6 to 6.5 years of difference in aging,” they wrote. “In addition, this difference approximately equates to the difference in brain volume between people with normal cognitive function and mild cognitive impairment.”

Does it matter?

Whoa, sounds like one can’t afford not to nap! But don’t stop reading to “hit the hay” in the hopes of bulking up your brain just yet. Other findings from the study suggest that this result may not truly be meaningful. After all, there was no difference between nappers and non-nappers in the volume of their hippocampus, a brain region key to memory formation and one of the first regions to suffer damage in Alzheimer’s disease. There was also no difference in the two measures of cognitive performance they used for comparison: reaction time and memory.

Professor Tara Spires-Jones, President of the British Neuroscience Association, said that the study was well-conducted, but had notable limitations.

“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.”

Additionally, as the brain is easily the most metabolically expensive organ in the body, it’s quite possible that people with larger brains simply need to nap more, rather than napping actually boosting their brain size.

The study’s modest findings, further tempered by the research’s limitations, likely did not deserve the media attention it received. A short nap (less than 30 minutes) certainly boosts cognitive function in the following hours. And multiple daily naps are a near necessity for young children. But don’t look to napping as a surefire way to buff up your brain.