Taking a nap during the day is “somewhat controversial,” according to Hassan Saeed Dashti, PhD, RD, of the Massachusetts General Hospital (MGH) Center for Genomic Medicine. It has been the subject of new research by Dashti and Iyas Daghlas, a medical student at Harvard Medical School (HMS) in collaboration with a team at the University of Murcia.

Dashti notes that some countries where daytime naps have long been part of the culture (such as Spain) it is now discouraged. At the same time , some companies in the United States now promote napping as a way to boost productivity.

The team has identified genes associated with sleep duration, insomnia, and the tendency to be an early riser or “night owl.”

To gain a better understanding of the genetics of napping, Richa Saxena and team at MGH and Marta Garaulet, PhD, of the department of Physiology at the University of Murcia, performed a genome-wide association study (GWAS), which involves rapid scanning of complete sets of DNA, or genomes, of a large number of people.

The goal of a GWAS is to identify genetic variations that are associated with a specific disease or, in this case, habit.

For this study, the MGH researchers and their colleagues used data from the UK Biobank, which includes genetic information from 452,633 people. All participants were asked whether they nap during the day “never/rarely,” “sometimes” or “usually.”

The GWAS identified 123 regions in the human genome that are associated with daytime napping.

A subset of participants wore activity monitors called accelerometers, which provide data about daytime sedentary behavior, which can be an indicator of napping. This objective data indicated that the self-reports about napping were accurate.

The researchers independently replicated their findings in an analysis of the genomes of 541,333 people collected by 23andMe, the consumer genetic-testing company. Also, a significant number of the genes near or at regions identified by the GWAS are already known to play a role in sleep. One example is KSR2, a gene that the MGH team and collaborators had previously found plays a role in sleep regulation.

Digging deeper into the data, the team identified at least three potential mechanisms that promote napping:

• Sleep propensity: Some people need more shut-eye than others.
• Disrupted sleep: A daytime nap can help make up for poor quality slumber the night before.
• Early morning awakening: People who rise early may “catch up” on sleep with a nap.

Hassan Saeed Dashti explained:

“This tells us that daytime napping is biologically driven and not just an environmental or behavioral choice. “

Some of these subtypes were linked to cardiometabolic health concerns, such as large waist circumference and elevated blood pressure, though more research on those associations is needed.

Several gene variants linked to napping were already associated with signaling by a neuropeptide called orexin, which plays a role in wakefulness. This is linked to rare sleep disorders such as narcolepsy.

The study led by investigators at Massachusetts General Hospital (MGH) is published in Nature Communications