In a lot of cases, health and lifestyle habits vary considerably from country to country. It's no secret, for example, that Americans approach diet and exercise differently from the French. Here in the States, we intersperse juice cleanses with bloomin' onions and hoof it to spin class, whereas they savor bites of unpasteurized triple-creme brie and walk off their meals with cigarettes in hand (this isn't a generalization at all).
But, trends in sleep habits appear to cross cultural and geographic divides, according to a new study published in the journal Science. Using a smartphone app, researchers from the University of Michigan collected demographic and sleep data from thousands of international users. Across the board, sex and age predicted how much and when people slept. And, Americans are hardly the only people disregarding their circadian clocks before bedtime.
Researchers set out two goals for the study: to show the scientific value of mobile tech and quantify the impact of social factors on sleep schedules. In this case, social factors encompass cultural norms (e.g., siestas, late family dinners) and other lifestyle characteristics affecting sleep, such as one's job schedule, that can't be explained by demographic information (age, sex) or light exposure.
Data for the study came courtesy of a University of Michigan-conceived smartphone app called ENTRAIN, which "recommends optimal lighting schedules for adjusting to new time zones" based on user-provided information about time zones, sleep schedules and exposure to outdoor and artificial light. More than 8,000 users from 20 countries voluntarily submitted their data for researchers to analyze. In the end, 45 percent of users hailed from the US, followed by nine percent from Australia and five percent from Canada. Europeans accounted for 15 percent of participants and the remaining five percent came from China, Japan and Singapore.
As a point of comparison, researchers also created theoretical models that predicted sleep patterns based on sunrise, sunset and light exposure. The models showed what users' sleep schedules would look like in the absence of social factors.
Here are some of their more interesting findings:
- Women reserve more time for sleeping, both through earlier bedtimes and later wake times.
- Average country bedtimes predicted average sleep duration (hour-per-night). Respondents from Australia and New Zealand reported the earliest bedtimes, followed by the US. American respondents said they went to bed around 11 o'clock, woke up at 6:50-ish and logged eight hours of rest. The longest night's sleep went to The Netherlands at 8.2 hours, followed by New Zealand, France and Australia, which all averaged slightly more than eight hours. Singaporeans reported getting the least sleep, at 7.5 hours-per-night, and the second-latest bedtime, at 11:45. Spaniards go to bed the latest.
- Theoretically, wake times should vary more than bedtimes from country to country due to different daily light cycles, but that wasn't the case. Bedtimes differed more, which suggested to researchers that people are hitting the sack later and getting less sleep because they're ignoring "biological clues" at night. "The discrepancies between theory and data," study authors wrote, "argue that solar cues are present but weakened around bedtime, but it's unclear whether weakening is a product of light-exposure modulation" or some other social pressure (e.g., 24/7 job demands or an Insta addiction.
- Starting between ages 20 and 24, people sleep less and go to bed earlier as they age. The effect was more pronounced during middle age, for men and for people who spend a lot of time in indoor lighting.
- Older people also have more consistent bedtimes and wake times than younger adults, who are more likely to change up their sleep schedules. Researchers surmised that older people stick to a schedule because they have a narrower circadian window for getting good sleep.
- Certain populations appear to be more sensitive to changes in timing of sunset and sunrise: women, older people and those who spend more time in outdoor lighting
We can't draw hard conclusions about global sleep habits based on a pool of self-selected users, whose answers may or may not represent the "average" sleeper in their home countries. Still, the findings depict the social factors affecting sleep in an interesting light.