By default, sleep is controlled by biology. Bedtime and wake time is regulated by one�s circadian clock, which is in turn controlled by exposure to light. But in modern industrialized society, people spend a lot of time indoors, away from natural light. At night, they use artificial light to stay awake long past dusk, and truncate sleep in the mornings with alarm clocks and smartphones.
As a result, sleep patterns are now affected by cultural factors, not just biological ones�and sleep culture varies considerably from one country to the next. So what do the data say about sleep habits around the world?
By analyzing data from users of a smartphone app designed to help people combat jet lag and adjust to new time zones, researchers have obtained accurate information about sleep habits around the world[1].
Over the course of a year, the study found that the Dutch get the most sleep, averaging 8 hours and 12 minutes�almost an hour more than in Singapore and Japan, where people sleep 7 hours and 24 minutes a night on average.
Wake times around the world don�t vary nearly as much as bedtimes do, the study found. In fact, differences in total sleep duration from one country to the next were explained almost entirely by differences in bedtime, not wake-up times. That is, the later the bedtimes, the less sleep people got.
An even bigger predictor of sleep duration is a person�s sex, the study found. Throughout the world and in almost every age cohort, women get more sleep, both going to bed earlier and waking up later than men.
Wake times are affected by sunrise and sunset, the study found, but bedtimes are affected much more strongly by societal factors. Biological cues around bedtime are ignored for social reasons, leading people to delay their bedtime and get less total sleep as a result.
Other comparative data about sleep patterns comes from Sleep Cycle, an app that uses the accelerometers on smartphones to monitor users� movements in bed and track their sleep and wake times. Between June 2014 and March 2015, Sleep Cycle gathered data from 941,000 users between 18 to 55 years old in 47 countries around the world[2].
The data showed that South Africans wake up earliest, averaging a wake time of 6:09am. Of the countries included, Brazil woke up the latest. Australians had the earliest bedtime; Spaniards the latest.
People wake up earliest on Monday�no surprise there. But as a result, people throughout the world sleep less on Sunday nights than they do on any other night of the week. In most parts of the world, the �best� night of sleep�that is, the calmest and deepest sleep, determined by monitoring movements in bed�happens Wednesday night, meaning people are most well-rested on Thursdays. And almost everywhere, the longest night of sleep happens Saturday night.
The app also allows users to record their mood when they awake. People are grumpiest on Tuesday mornings, the data showed, not Mondays. Americans and Canadians wake up happiest on Saturday morning, the data found, though most of the rest of the world is happiest Sunday morning.
?References
1. Walch, O.J., Cochran, A., & Forger, D.B. (2016). A global quantification of �normal� sleep schedules using smartphone data. Science Advances, 2.
2. Sleep Cycle (2015). How the world sleeps: Days of the week.
