Daytime napping frequency is partly determined by genetics, according to the largest study of its kind led by researchers at Massachusetts General Hospital (MGH). Collaborating with experts from the University of Murcia in Spain and other institutions, the MGH team identified dozens of gene regions linked to daytime napping. They also found preliminary evidence connecting sleep habits to cardiometabolic health.
“Napping remains controversial,” says Hassan Saeed Dashti, co-lead author alongside Iyas Daghlas, a medical student at Harvard Medical School (HMS). Dashti points out that cultures like Spain, with traditional siestas, are now discouraging them, while some U.S. companies promote naps for productivity. “Understanding the biological drivers behind napping was crucial,” Dashti explains.
Building on prior work, co-senior author Richa Saxena, PhD, from the Saxena Lab at MGH, and her team—including co-senior author Marta Garaulet, PhD, from the University of Murcia's Department of Physiology—conducted a genome-wide association study (GWAS). This analyzed complete genomes from hundreds of thousands to pinpoint genetic variations tied to napping habits. Previously, they've linked genes to sleep duration, insomnia, and chronotypes like early risers or night owls.
Using data from the UK Biobank's 452,633 participants, who self-reported napping as 'never/rarely,' 'sometimes,' or 'usually,' the GWAS pinpointed 123 genomic regions associated with daytime napping. Objective validation came from accelerometers on a subset, tracking sedentary behavior as a napping proxy, confirming self-reports. “This added strong validation to our findings,” Dashti notes.
Results were replicated in 541,333 additional genomes, and many identified genes are known to influence sleep, such as KSR2, previously tied to sleep regulation by the MGH team.
Digging deeper, the researchers identified at least three biological mechanisms driving napping:
Sleep propensity: Some individuals naturally require more sleep.
Disrupted nighttime sleep: Daytime naps compensate for poor prior sleep.
Early rising: Early wake times lead to naps for catch-up rest.
“These insights show napping is biologically driven, not just a lifestyle choice,” Dashti says. Certain napping subtypes correlated with cardiometabolic risks like larger waist circumference and higher blood pressure, warranting further study.
Additionally, napping-linked gene variants involve orexin signaling, key to wakefulness. “While major disruptions cause disorders like narcolepsy, subtler changes may explain napping variations,” Daghlas adds.
