To uncover this link, the researchers culled data from the UK Biobank (which has input from nearly 379,000 people) and identified the people who had particular snippets of DNA known to predispose a person to nap on the regular. (By using genetics, they could avoid the issue of confounding lifestyle factors that might affect the connection between napping and cognition.) Then, they analyzed brain data from the Biobank set (including brain MRI scans) for the people who had the napping genes versus those who didn’t—and they found that the folks predetermined to nap had significantly larger brains.
Napping may provide a defense against neurodegeneration
This connection between habitual napping and brain size represents a key finding because the volume of the brain shrinks as we age, impacting memory performance and cognitive function (and that process happens at a faster clip in folks with cognitive decline or neurodegenerative disease). “Based on our findings, we hypothesize that napping regularly provides some protection against neurodegeneration by compensating for poor sleep,” says lead author on the study and PhD candidate Valentina Paz, MSc, a researcher at Uruguay's University of the Republic and University College London.
“We hypothesize that napping regularly provides some protection against neurodegeneration by compensating for poor sleep.” —Valentina Paz, MSc, researcher at University of the Republic, Uruguay
More broadly, this finding suggests that taking regular naps may help us better retain our brain size as we age—and stave off cognitive decline as a result. “Brain volume measures have been used as markers of neurodegeneration, so a larger brain volume implies less degeneration,” says Paz. “Understanding this difference in brain size [in people who nap versus those who don't] has important clinical implications for mitigating age-related cognitive impairments.”
Interestingly, Paz and her co-researchers did not find a similar tie between a person’s genetic likelihood for habitual napping and other elements of brain health, like the size of the hippocampus (which is an important area for memory), reaction time, and visual memory.
For that reason, Paz says the link between frequent daytime napping and brain health is still being untangled. It’s also important to note that this study didn’t take into account factors like the presence of sleep inertia, the quality of the prior sleep period, or the length and timing of naps—all of which could influence whether a nap has a positive, negative, or null effect on cognition.
With regard to brain volume, though, it's worth reiterating that this finding is significant. Considering the typical rate at which we tend to lose brain volume with age, the study researchers were able to calculate that the difference they identified in brain volume between the habitual nappers and the non-nappers was equivalent to roughly 2.6 to 6.5 years of aging. “This difference approximately equates to the difference in brain volume observed between individuals with normal cognitive function and those exhibiting mild cognitive impairment,” says Paz.
Such a potential brain boost from napping falls in line with previous research indicating that napping can enhance certain elements of cognition, particularly in people who are learning new information, says neurologist Brian Murray, MD. "There is something about sleep that helps consolidate and organize the brain," he says.
How to optimize your naps for cognitive health
In the spirit of boosting the beneficial effects of daytime rest on the brain, Paz says it’s important to consider not just that you nap but how you nap.
In general, it’s best not to overdo it. Paz advises a short nap of five to 15 minutes (and no more than 30 minutes max) in length; this way, you won't risk dipping into the deeper sleep stages, from which it'll be tougher to wake up.
It's also smart to nap sometime in the early afternoon, says Paz, ideally around 2 or 3 p.m. (if you typically go to bed around 10 or 11 p.m.). Previous research has found that this “post-lunch dip period” is the optimal time to take a nap, says Paz, in order to overcome the all-too-common slump in alertness and performance around midday. Also, avoiding a nap too late in the day ensures you won't use up some of your sleep drive and potentially interfere with your ability to fall asleep that night.
For the best quality nap, Paz prescribes a comfortable environment in which light, temperature, and noise are taken into consideration. In particular, it's best to choose a quiet, cool, and dark room for a nap; if your space is loud, you can turn on some white noise to mask external sounds, and if it's bright, try slipping on an eye mask for darkness.
Further details on nailing the ideal nap for health purposes will require additional research, says Paz. But in the meantime, the new study represents a big step forward in linking habitual napping with larger total brain volume and in turn, a healthier brain. “Using different datasets and methodologies, we will continue investigating the association between napping and overall health,” says Paz, who is determined to shed more light on the "gray area" of our gray matter.
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