I was always an early riser, but having to be at the hospital by 5 or so AM refined that predisposition. A new study of sleep shows that when we go to bed, how long it takes to fall asleep, and countless other measures of our biological need to sleep are part genetic and part cultural.
We all need sleep; it is a biological imperative right up there with eating and reproducing. A recent study I reported indicated that we sleep 9.1 hours a day. But the amount varied by age and geography. A meta-analysis of sleep studies involving twins suggests that roughly 45% of our sleep quality and duration is determined by our genes. The rest from our daily activities and, if this new paper is to be believed, our culture – at least at the country level.
The data comes from sleep data involving over 220,000 individuals based on a wearable, the Qura ring. As with other wearables, like an Apple Watch or Fitbit,
“Sleep was inferred using proprietary algorithms that consider motion, heart rate variability and body temperature, combined with a circadian factor that incorporates expected sleep timing.”
You may apply uncertainty as you wish.
Another limitation we should specify at the outset is that these trackers can be expensive, and the population sample tends to be from higher socioeconomic groups who are also more tech-savvy, health-conscious, and young. That said, there is no reason to believe that these generalities about the population differ from country to country. Additionally, some data was collected during the COVID pandemic, when individuals “were under some degree of movement restriction.”
Oura collected over 50 million nights of sleep across 35 nations over one year , 2021. The population's average age was 44, with the majority “working-age adults between approximately 30 and 55 years old.” 60% were male, and each individual contributed roughly 240 nights of sleep data. The aggregate sample working age adults
- Women sleep longer than men by roughly 25 minutes—seven hours to men’s six and two-thirds hours.
- People in Asia slept 45 minutes less than the rest of the world, tending to fall asleep and awake later. Europeans were in the middle, while those individuals in North America slept the most, going to sleep and waking earlier.
- Sleep efficiency was a calculation of the time “in bed that is actually spent asleep.” Shorter sleep times were associated with lower sleep efficiency – more tossing and turning. While the range of sleep efficiency varied based on effect size, it was most pronounced based on country and gender. At 87%, women were slightly more efficient than men at 84%. Slovakia had the most efficient sleepers (87%), Japan the least (84%)
- The time spent in bed included the time necessary to fall asleep, roughly 11 minutes, and the time spent awake after falling asleep, approximately 43 minutes - termed wake after sleep onset or WASO. WASO was the more significant contributor to sleep efficiency and showed geographic variation; Europeans tossed and turned the least; Asians, an average amount, but coupled with shorter sleep periods, it resulted in less sleep efficiency.
- There was, as might be expected, variability in individual sleep times. This variability was greatest for people in Asia least for Europeans, with North Americans somewhere in between. Higher variability was associated with shorter sleep.
It is widely believed that we “catch up on our sleep” on the weekends when we no longer have work requirements. This sleep extension on weekends or days off work has been termed “social jetlag.” Because some party hearty on the weekends, resulting in going to bed later, sleep duration is the best measure of our “sleep debt.”
“…weekend sleep extension should be greater in both individuals and countries where weekday sleep is shorter.”
That was only partially true.
People generally slept longer, fell asleep, and woke up later on weekends. The total sleep during the week had the greatest impact on weekend sleep extension, so we do catch up. But other factors were at play.
We tend to catch up less as we age, and countries, as a measure of culture, also impact us.
While the researchers note that many socio-cultural factors influence our sleep,
“work itself and work culture (in particular, the distinction between work and non-work time) may play a considerable role in the cross-country differences in sleep patterns.”
Our workload, in terms of hours, varies. The average in the US is 1729 hours, 43 40-hour work weeks annually; in Asia, 2076 hours, 52 40-hour work weeks annually. Europe leads the way in “work-life” balance issues with labor protections concerning work and non-work time. . The researchers feel these differences in cultural norms of that division of work and life account for some of the differences in weekend sleep extension.
Getting a good night’s rest is just as standard a recommendation as watching between-meal treats or eating a balanced diet. But determining an optimum number of hours, that Goldilocks amount that reduces our risk of poor health to a minimum but still leaves us with time to enjoy all that extra life, remains elusive.
Last word to the researchers,
“Our results are consistent with recent research suggesting that socio-cultural factors account for over 50% of the variance in sleep quality and quantity across 11 high-income countries. The present findings are also consistent with research demonstrating that what is considered ‘normal sleep’ differs around the world, and that it should not be defined solely according to norms or ideals derived from Western sleep research.”
 “People at higher latitudes sleep longer in the winter than in the summer because of changes in photoperiod length; therefore, we analyzed data across a whole year to minimize the impact of seasonal variation.”
 The Oura users in Europe worked only 1 40-hour week less than those in the US, suggesting either the idea that Europeans work far less than us is untrue or that we are looking at a very work-driven study population.
Source: Country differences in nocturnal sleep variability: Observations from a large-scale, long-term sleep wearable study Sleep Medicine DOI: 10.1016/j.sleep.2023.08.010