Participants were asked how often they napped during the day and were given three choices – never/rarely, sometimes or usually. Some were also asked to wear an activity monitor, or accelerometers, to make sure they reported their snoozes accurately.

GWAS identified 123 regions in the human genome, which were associated with having a sleep during the day. A large number of these regions were already associated with snoozing, which reassured scientists they were on the right track.

Digging deeper into the data, they identified three potential napping mechanisms. The first two, dubbed “disrupted sleep” and “early morning awakening” refer to people who nap because they haven’t had enough shut eye the night before, or because they get up very early in the morning.

Dr Dashti said: “This tells us that daytime napping is biologically driven and not just an environmental or behavioural choice.”

Some of the genetic traits identified were also linked to health concerns, including obesity and high blood pressure. Meanwhile, several of the napping gene variants were associated with orexin, a neuropeptide, linked to wakefulness.

Co-author graduate student Iyas Daghlas from Harvard Medical School said: “This pathway is known to be involved in rare sleep disorders like narcolepsy, but our findings show that smaller perturbations in the pathway can explain why some people nap more than others.”