What Is The Optimal Amount Of Sleep? A 20-Country Study Shows It’s More Complicated Than You Think

Quick Summary

• The ideal amount of sleep for optimal health isn't the same everywhere; a large-scale international study shows that it varies significantly from country to country.

• Researchers found no evidence that countries with shorter average sleep durations suffer from worse national health outcomes like higher rates of heart disease or shorter life expectancies.

• Your personal health may be linked to how well your sleep habits align with your culture's norms, a concept known as "cultural fit." People whose sleep duration was closer to their country's perceived ideal reported better overall health.

The Optimal Amount Of Sleep For Health

For decades, we’ve been told that eight hours is the magic number for a healthy night's sleep. It’s a simple, memorable rule that has become a defacto global standard for good sleep health, despite it likely being a myth. But what if the ideal amount of sleep isn't a one-size-fits-all prescription?

A major study challenges this long-held belief, suggesting that our sleep needs might be more flexible and deeply influenced by the culture we live in. The research, published in the Proceedings of the National Academy of Sciences, explored sleep patterns and health outcomes across dozens of countries (Ou et al., 2025).

So what did the researchers find about sleep quantity and health across countries?
First, if there is a standard human sleep need, is there an optimal amount of sleep that shows up across all countries?

Does Everyone Around The World Get The Same Amount Of Sleep?

No, research shows that average sleep times vary significantly between countries, sometimes by more than 90 minutes a night. These differences have been shown time and again using a wide variety of methods, from self-report surveys to data from activity monitors and smartphone apps (Ou et al., 2025; Walch et al., 2016).

The 2025 study by Ou and colleagues confirmed this pattern by surveying nearly 5,000 people across 20 different countries. They found a wide range in average sleep duration, from 7 hours and 52 minutes in France on the high end, down to just 6 hours and 18 minutes in Japan on the low end.

That’s a difference of one hour and 34 minutes every single night.

Rank	Country	Average Sleep Duration
1	France	7 hours, 52 minutes
2	Spain	7 hours, 45 minutes
3	Australia	7 hours, 43 minutes
4	UK	7 hours, 40 minutes
5	Canada	7 hours, 38 minutes
6	Belgium	7 hours, 35 minutes
7	Germany	7 hours, 32 minutes
8	Sweden	7 hours, 30 minutes
9	USA	7 hours, 28 minutes
10	Netherlands	7 hours, 25 minutes
11	Italy	7 hours, 22 minutes
12	Poland	7 hours, 18 minutes
13	Mexico	7 hours, 15 minutes
14	Brazil	7 hours, 12 minutes
15	Singapore	7 hours, 05 minutes
16	Hong Kong	6 hours, 55 minutes
17	China	6 hours, 45 minutes
18	South Korea	6 hours, 35 minutes
19	Taiwan	6 hours, 30 minutes
20	Japan	6 hours, 18 minutes

This trend, where countries in East Asia tend to report the shortest sleep durations and those in Western Europe and Oceania report the longest, has been observed in many previous studies and even appears in infants and children, suggesting these patterns are established early in life (Mindell et al., 2010).

But if people in some countries are sleeping so much less, are they less healthy as a result?

Do Countries With Shorter Sleep Have Worse National Health?

Surprisingly, no. The research by Ou et al (2025) found that countries with shorter average sleep durations do not have higher rates of heart disease, diabetes, or shorter life expectancies.

To investigate this, researchers conducted a detailed review, where they gathered the results of 14 previous large investigations on sleep, which included data from 71 different countries. They then compared these national average sleep times with several key measures of a nation's health:

• Mortality rates from ischemic heart disease, a condition where the heart doesn't get enough blood.

• National obesity rates.

• National diabetes rates.

• Average life expectancy.

After controlling for other important factors like national wealth, nutrition, and inequality, the results were unexpected. There was no significant link between a country's average sleep time and its rates of heart disease, diabetes, or life expectancy.

Even more curiously, the study found that countries where people slept longer actually had higher rates of obesity. This is the exact opposite of the relationship typically found within countries, where shorter sleep is often linked to a higher risk of obesity.

It's important to approach this kind of country-level comparison with a bit of caution due to a potential statistical pitfall known as the ecological fallacy. This is the assumption that a trend seen in a large group (like a country) must also be true for the individuals within that group. For example, just because the average wealth of a city is high, it doesn't mean every person who lives there is wealthy. So the country-level data gives us a fascinating clue, but it doesn't tell the whole story.

So, to get a clearer picture, what happens when you look at individuals within different countries?

What Is The Relationship Between Sleep Duration and Health For Individuals?

For individuals, the relationship between sleep and health is typically U-shaped, meaning both sleeping too little and sleeping too much are linked to worse health. This pattern has been well-established in sleep science for years.

Numerous large studies have found that people at the extremes of sleep duration, those getting very few hours and those getting very many, have higher risks for poor health, including a higher risk of death (Gallicchio & Kalesan, 2009; Cappuccio et al., 2010).

Think of it like a "Goldilocks" effect: there’s a sweet spot in the middle that is "just right" for optimal health.

The research by Ou and colleagues (2025) confirmed this U-shaped curve was present in all 20 countries they surveyed. They created a composite health score for each participant, which combined measures of mental health, depression, subjective health, and the number of chronic health conditions. In every single country, this health score was highest for people sleeping a moderate amount and lower for those sleeping the least and the most.

This suggests that the fundamental U-shaped link between sleep duration and individual health is a consistent pattern across cultures.

But if the U-shaped curve is potentially universal, does that mean the "sweet spot" for sleep is the same for everyone?

Is There An Optimal Amount of Sleep That Is Universal Across Cultures?

No, the specific amount of sleep linked to the best health outcomes, the "sweet spot" at the bottom of the U-shaped curve, is different in each country. This is one of the most important findings from the research.

Researchers calculated the precise point on the curve where health was at its peak before it began to decline with more sleep. They called this the "turning point." When they compared these turning points across the 20 countries in their study, they found a significant variation.

In other words, the amount of sleep associated with the best health in Japan was different from the amount associated with the best health in France or Canada.

This suggests that while the pattern of the sleep-health relationship is universal (the U-shape), the specifics of what makes up an ideal amount of sleep are shaped by local, cultural factors.

Interestingly, the study also revealed another consistent pattern: in every single one of the 20 countries, the average person slept less than their country's calculated "optimal" amount. This indicates a common tendency for people to get slightly less sleep than what might be best for their health, regardless of their cultural background.

If the ideal amount of sleep isn't a fixed biological number, what else could be influencing its connection to our health?

What Is 'Cultural Fit' And How Does It Affect Sleep And Health?

"Cultural fit" refers to how closely an individual's behaviors match the habits and expectations of their culture, and the 2025 study suggests that people whose sleep duration is closer to their country's perceived ideal report better health.

To measure this, the researchers asked participants not only how much they slept, but also how much sleep they believed was considered ideal in their country. They then calculated the difference between a person's actual sleep time and this perceived cultural ideal. The smaller the difference, the better their "cultural fit."

The results showed a clear connection: people whose sleep habits were more in line with their local cultural norms had higher composite health scores.

This introduces an interesting new layer to our understanding of sleep. It’s not just about the absolute number of hours you get; it’s also about how your sleep patterns compare to the unwritten rules and expectations of the society around you.

Why would this be the case? The researchers suggest a few possibilities:

• Subjective Well-being: People may simply feel psychologically better and healthier when they believe their behaviors are normal and socially appropriate.

• Reduced Social Friction: Being in sync with your culture's sleep-wake schedule can reduce practical stress. For example, if you sleep much later than is typical in your culture, you might experience more stress related to commuting, morning appointments, or work start times.

• Underlying Factors: It's also possible that a third factor is at play. For instance, people who are less healthy to begin with might find it harder to conform to their society's ideal sleep patterns.

While exactly how this works is still unclear, this finding strongly suggests that cultural context is a key, and previously overlooked, ingredient in the recipe for healthy sleep.

What does this all mean for the common advice we hear about getting eight hours of sleep?

So, How Much Sleep Do I Really Need?

This research suggests there isn't one single number that's right for everyone, as our sleep needs appear to be flexible and are influenced by our cultural environment. The 7 - 9 hours can be a useful starting point, but it should be seen as a general guideline, not an unbreakable law.

The key takeaway is that the relationship between sleep and health is more complex than we thought. Cultural norms appear to shape not only how much we sleep, but also the very definition of what a "healthy" amount of sleep is in a particular place.

This adds to a growing body of evidence suggesting that our need for sleep is not a rigid requirement but a flexible system that adapts to our environment (Fjell & Walhovd, 2024).

Ultimately, the best amount of sleep for you is the amount that allows you to wake up feeling rested and function well throughout the day. This research empowers us to look beyond a single number and consider the broader context of our lives, including our culture, in understanding our personal sleep needs.

Where To From Here?

If you've ever felt that the standard "8-hour rule" doesn't quite work for you, or that your sleep needs seem different from those of people around you, this research shows you might be onto something. The connection between our sleep, our health, and our cultural environment is real and complex. Trying to force a single rule onto your own body can be frustrating and, as this study suggests, may not even be the right goal.

Understanding these small but important differences is the first step, but applying them to your own life can be challenging. This is where working with a specialist can be invaluable. A Behavioral Sleep Medicine provider moves beyond one-size-fits-all advice. They work with you to develop a personalized plan that focuses on the specific reasons for your sleep issues.

This process involves looking at your unique biology, your daily behaviors, your thought patterns around sleep, and as we now see, even the broader cultural context you live in. The goal is not to make you fit a generic sleep schedule, but to help you discover and consistently achieve the sleep that leaves you feeling your best.

Frequently Asked Questions About Optimal Amount Of Sleep And Culture

Q1:  Is 8 hours of sleep a universal rule for good health?

A1: No, the idea that everyone needs exactly eight hours of sleep is not a universal rule. New research shows that the "perfect" amount of sleep for optimal health varies significantly from one country to another, suggesting our sleep needs are flexible and influenced by our culture (Ou et al., 2025). While the 7 - 9 hour recommendation can be a useful starting point, it should be treated as a general guideline, not a strict requirement for everyone.

Q2: How much do people sleep in different countries?

A2:  Average sleep times differ substantially around the world, often by more than 90 minutes per night. For example, a large international study found that people in France slept an average of 7 hours and 52 minutes, while people in Japan averaged just 6 hours and 18 minutes (Ou et al., 2025). This pattern, with East Asian countries reporting shorter sleep times and Western European countries reporting longer ones, has been confirmed by many studies using different methods (Walch et al., 2016).

Q3: Are people in countries with less sleep less healthy?

A3:  Surprisingly, no. A major analysis found no evidence that countries with shorter average sleep durations have worse national health. Researchers compared national sleep data to rates of heart disease, diabetes, and life expectancy and found no significant link (Ou et al., 2025). In fact, they found that countries where people slept longer tended to have higher rates of obesity, which is the opposite of the trend seen in individuals.

Q4: What is the "U-shaped" relationship between sleep and health?

A4: The "U-shaped" relationship describes how both sleeping too little and sleeping too much are linked to worse health outcomes. The healthiest individuals are typically those who sleep a moderate amount - the "sweet spot" at the bottom of the "U." This pattern has been confirmed in numerous studies and was found to be consistent across all 20 countries in a recent major study (Ou et al., 2025; Gallicchio & Kalesan, 2009).

Q5: Is the "optimal" amount of sleep the same for everyone?

A5: No, the optimal amount of sleep for the best health is not the same for everyone. While the U-shaped pattern is universal, the specific "sweet spot" for sleep duration varies between countries. For instance, the amount of sleep linked to the best health in Japan is different from the amount linked to the best health in Canada (Ou et al., 2025). This suggests that cultural factors help shape what a healthy amount of sleep looks like in different parts of the world.

Q6: What does "cultural fit" mean for sleep and health?

A6: "Cultural fit" refers to how well your personal habits match the norms and expectations of your culture. In the context of sleep, people whose sleep duration was closer to what is considered ideal in their country reported better overall health (Ou et al., 2025). This suggests that our health isn't just affected by the absolute number of hours we sleep, but also by how well our sleep patterns align with the society around us.

References

Cappuccio, F. P., D’Elia, L., Strazzullo, P., & Miller, M. A. (2010). Sleep duration and all-cause mortality: A systematic review and meta-analysis of prospective studies. Sleep, 33(5), 585–592.

Fjell, A. M., & Walhovd, K. B. (2024). Individual sleep need is flexible and dynamically related to cognitive function. Nature Human Behaviour, 8, 422–430.

Gallicchio, L., & Kalesan, B. (2009). Sleep duration and mortality: A systematic review and meta-analysis. Journal of Sleep Research, 18(2), 148–158.

Mindell, J. A., Sadeh, A., Wiegand, B., & How, T. H. (2010). Cross-cultural differences in infant and toddler sleep. Sleep Medicine, 11(3), 274–280.

Ou, C., Lou, N. M., Maheshka, C., Shi, M., Takemura, K., Cheung, B., & Heine, S. J. (2025). Healthy sleep durations appear to vary across cultures. PNAS, 122(19), e2419269122.

Walch, O. J., Cochran, A., & Forger, D. B. (2016). A global quantification of “normal” sleep schedules using smartphone data. Science Advances, 2(5), e1501705.

Written By Dan Ford, Sleep Psychologist

Published By The Better Sleep Clinic