How much sleep do you really need? It appears to depend on your culture

New research published in the Proceedings of the National Academy of Sciences raises questions about the common belief that everyone needs the same amount of sleep to stay healthy. By analyzing sleep and health data from thousands of people across multiple countries, the researchers found that the amount of sleep linked to better health varied between cultures. The findings suggest that people might be healthier when their sleep patterns align with the expectations and norms of their cultural environment—even if those norms differ across societies.

The research team, led by Steven Heine at the University of British Columbia, was motivated by a long-standing question: Why do people in different countries sleep so differently, and what does that mean for their health? While many sleep guidelines recommend a standard eight hours of sleep per night, cross-national studies consistently show that average sleep duration varies dramatically.

“I’ve lived in Japan for several years and it was always striking how little people seemed to be sleeping there. On the other hand, Japan has the longest average lifespan in the world, so it seemed surprising that they didn’t seem to be suffering from their short sleep durations,” explained Heine, a professor of social and cultural psychology at the University of British Columbia and author of Start Making Sense.

To explore this puzzle, the researchers conducted two separate investigations. The first study analyzed national averages of sleep duration from 14 previous cross-cultural studies. These studies used a variety of methods, from sleep-tracking apps to national surveys, and included data from over 70 countries. In total, the researchers gathered 353 national sleep averages, which were then compared with national health statistics, such as rates of heart disease, obesity, diabetes, and life expectancy.

Importantly, the researchers accounted for other factors that might affect health outcomes, including national wealth, income inequality, nutritional status, and a country’s latitude. These controls allowed them to test whether sleep duration itself could predict health outcomes at the national level.

Surprisingly, they found that average national sleep duration was not a reliable predictor of health. Countries with shorter average sleep times, like Japan, did not have higher rates of heart disease or lower life expectancy than countries where people sleep longer. In fact, longer sleep durations were associated with higher national obesity rates—a result that runs counter to what studies within individual countries have typically shown.

These findings raised the possibility that relationships between sleep and health might look different when zooming out to the national level. To test this further, the researchers designed a second study that focused on individual-level data collected across 20 countries. They surveyed nearly 5,000 adults between the ages of 25 and 60 about their sleep patterns, physical and mental health, and their perceptions of what constitutes an ideal amount of sleep in their culture. The survey was conducted during the week of the autumnal equinox to help control for daylight variation.

Participants were asked both how long they slept the night before and how much they typically sleep each day, including naps. They also reported on a range of health indicators, including body mass index, depression, chronic health conditions, and overall well-being. The survey also included several control variables such as age, gender, income, smoking, drinking, and the latitude of each participant’s location.

The researchers found that individual sleep duration was positively associated with better health. People who reported sleeping longer the night before tended to have fewer chronic health conditions, better mental health, and lower levels of depression. However, there was a turning point: too much sleep was also linked to worse health, creating a U-shaped curve. This pattern was consistent with earlier studies showing that both short and long sleep durations can be linked to negative health outcomes.

The amount of sleep associated with optimal health varied across countries. In each of the 20 countries studied, the optimal sleep duration—that is, the point on the curve where health was best—was different. These turning points were always higher than the average sleep duration reported in each country, suggesting that most people sleep less than what would be ideal for their health. But the “ideal” varied from place to place, supporting the idea that sleep needs are not fixed across cultures.

Another key finding was that people who slept closer to what they believed was their culture’s ideal sleep duration tended to report better health. This idea, known as cultural fit, suggests that aligning with local norms—even for something as private as sleep—may offer psychological or physiological benefits. It is possible that people feel healthier when they believe they are behaving in socially appropriate ways, or that being out of sync with social routines, such as public transportation schedules or work start times, creates stress that impacts health.

Interestingly, the researchers did not find that country-level sleep averages predicted better or worse individual health. This finding, which mirrors the results of the first study, challenges the assumption that countries with shorter average sleep durations must be less healthy. It also highlights the risks of drawing conclusions from national averages—what holds true for individuals within a country may not hold true between countries, a concept known as the ecological fallacy.

The findings provide evidence that “the amount of sleep that is associated with good health varies substantially across cultures,” Heine told PsyPost. “People who sleep closer to their own cultural norms tend to have better health. We were expecting these findings, given some of our previous research, but we were still struck by just how much variation there is in sleep duration. In our sample, French people slept more than an hour and a half longer than Japanese people.”

Although the study provides new insights into how culture shapes sleep and health, it comes with limitations. Most of the data on sleep and health were self-reported, which can be influenced by social desirability or cultural expectations. People may also misreport their sleep habits, particularly in countries where long sleep is frowned upon. And while they controlled for several key variables, it’s likely that many other cultural and environmental factors influence both sleep and health in ways that were not captured by the study.

Looking ahead, the researchers hope to better understand how cultural practices affect not just how long people sleep, but how they sleep. They are particularly interested in whether different cultural patterns are associated with different distributions of sleep stages, such as deep sleep and rapid eye movement (REM) sleep, which could help explain how people maintain health with varying amounts of sleep.

“If Japanese can get enough sleep despite sleeping 90 minutes less than the French, then this suggests that they must spend different amounts of time in the different stages of sleep,” Heine said. “We’re hoping to be able to compare how the sleep cycle through the various stages of sleep are shaped by culture.”

“I find it curious that people are affected by their cultural norms for sleep because sleep is a relatively private aspect of our lives. Perhaps we learn our cultural norms from how society is structured, such as when offices are open and when public transit starts.”

The study, “Healthy sleep durations appear to vary across cultures,” was authored by Christine Ou, Nigel Mantou Lou, Charul Maheshka, Marc Shi, Kosuke Takemura, Benjamin Cheung, and Steven J. Heine.