People whose genes are linked to habitual napping have a larger total brain volume overall, a new study shows — reducing the stigma against naps.
But the research does not demonstrate they are mentally sharper or protected against the shrinking brain volume associated with ageing and dementia.
People genetically predisposed to be habitual nappers in this study did not have faster reactions, superior visual processing or a bigger hippocampus (the brain region associated with long-term memory).
The team noted, however, that a larger brain volume is a “marker of good brain health linked to a lower risk of dementia and other diseases”.
They 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”.
“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,” stated senior author Dr Victoria Garfield, from the University College of London.
“I hope studies such as this ... can help to reduce any stigma that still exists around daytime napping.”
Some people who cannot control their sleep need a nap licence.
— Dr Dale Rae, UCT sleep scientist
However, Dr Dale Rae, a sleep researcher at the UCT Neuroscience Institute, flags habitual daytime napping by most adults as a “sign that something is wrong”, for example, acute or chronic sleep deprivation, or other health problems.
Certain groups, for example new parents, are the exception to this.
“The priority is to look for good quality nocturnal sleep, but some people who cannot control their sleep need a nap licence,” said Rae, listing shift workers, new parents, adolescents and athletes as among those who may need catch-up sleep while the sun is up.
“People who are ill may also need to nap as sleep is the body’s response to dealing with infection and underlying disease,” she said.
The latest research by the University College London and the University of the Republic, in Uruguay, is based on an analysis of 97 snippets of DNA linked to habitual napping.
The study points to “a causal link between habitual napping and larger total brain volume”, says the lead author Valentina Paz, from the University of the Republic and the MRC Unit for Lifelong Health & Ageing at UCL.
The genetic variants were identified based on people’s self-reported napping habits, backed by recordings from wrist-worn accelerometers.
20% of sleep should be deep sleep, and 25% should be REM sleep (sleep stage with dreaming).
— Sleep quality counts
The data was taken from more than 378,000 people in the UK Biobank study, aged 40 to 69 years old, of white European ancestry — one of the limitations of the peer-reviewed research, published in the journal Sleep Health.
Previous studies have suggested people who take short naps of 30 minutes or less have better cognitive performance in the hours after their rest than those who did not nap.
Many studies have looked at napping and cognitive function, for example, improving memory, but their results are “not black and white”, said Rae, though daytime sleep can sometimes support memory storage.
“Sleep has an important role in moving shorter-term memory to longer-term memory,” she said.
Rae said: “The true test of whether people are sleeping enough is their daytime functioning and sleepiness. Sleep quality counts more than quantity.
“Daytime napping is generally considered an unhealthy habit, like taking stimulants [coffee] to improve alertness, and a sign that life is so hectic that you are forced to pay back your sleep debt during the day.
“But the odd nap early in the day, especially if you are fit and active, is fine, like enjoying a chocolate. This is not something you build your diet [or day] around.”
Support independent journalism by subscribing to the Sunday Times. Just R20 for the first month.
Would you like to comment on this article?
Sign up (it's quick and free) or sign in now.
Please read our Comment Policy before commenting.