Are Eight Hours of Sleep Necessary for Good Health?

Sleep researchers have known for years that people in Japan sleep significantly less than people in the United States, Canada, and most European countries. In one study that recorded sleep patterns with a smartphone app, Japanese participants slept 25 minutes less, on average, than Americans and 40 minutes less than Dutch participants (Walch, Cochran, & Forger, 2016). In another study, Japanese infants and toddlers slept one hour less than their Western counterparts (Mindell et al., 2010).

Studies have also found that individuals who sleep less than the recommended eight hours a night are generally less healthy, both physically and mentally. Given this apparent biological fact, we should expect Japanese individuals who sleep six to seven hours a night to be less healthy than their North American counterparts.

But they aren’t. As a group, the Japanese live considerably longer than North Americans. They also have significantly lower rates of obesity, type 2 diabetes, and heart disease (Cheung et al., 2021).

The Sleep-Health Paradox

How can we explain this paradox? In study after study, sleeping eight hours is associated with better health. Yet Americans who sleep eight hours are, on average, less healthy than Japanese who sleep six to seven hours a night. What’s going on?

Let’s begin with the obvious. Americans eat more red meat, dairy products, and high-carb snacks, whereas Japanese eat more fish, fruits, and vegetables. In addition, portion sizes in the U.S. are larger than in Japan. These culturally shaped eating habits explain some of the differences in overall health, but they don’t explain the entire difference. Something else is probably going on.

In the United States, there’s a widespread belief that sleeping eight hours a night is important. When I was in college, I established a scrupulous sleep schedule—at least seven hours every night—even when I had to write a paper or study for an exam. I never once pulled an all-nighter.

The situation in Japan is very different (Cheung et al., 2021). In Japanese culture, a commonly held view is that sleep is a luxury, not a necessity. Japanese high school students preparing for difficult university entrance exams often say, “Yontou, goraku,” which means “You pass with four [hours of sleep] but fail with five.” Confucian teachings state that sleeping less is essential for effective functioning. In Japan, sleep can be—and should be—sacrificed in the pursuit of success.

Do Japanese Students Actually Sleep Less?

A few years ago, a team of Canadian and Japanese researchers led by Benjamin Cheung at the University of British Columbia examined cultural attitudes toward sleep and their relationship to sleep duration (Cheung et al., 2021). They recruited 295 students from universities in Canada and Japan—131 European Canadians, 67 Asian Canadians, and 97 Japanese. Most of the study participants were between the ages of 17 and 27.

The participants wore a special watch that recorded how many hours they slept each day. They also responded to questions about the ideal amount of sleep in their culture, their perception of the relationship between sleep and health, and their own personal health.

The results of the study were unambiguous. On average, the Japanese students slept about six hours a day, significantly less than the Canadian students, who slept about seven hours a day. The Japanese students also reported fewer symptoms of illness, such as headache, stomach pain, and shortness of breath. In short, the Japanese students as a group slept less but were somewhat healthier than the Canadians.

Cultural Differences in Beliefs About Sleep

Benjamin Cheung and his team also uncovered cultural differences in beliefs related to sleep. Specifically, Japanese students said the ideal amount of sleep in their culture is something less than seven hours. They also said there is a weak positive relationship between the amount of sleep and physical health.

Canadian students said the ideal amount of sleep in their culture is about eight hours. In their view, a strong positive relationship exists between the amount of sleep and physical health.

Cheung and his team cleverly designed their study to rule out the possibility that the observed differences were due to biological or genetic differences between Canadians and Japanese. You may recall that one of their three samples consisted of Asian Canadian students. These students were biologically comparable to Japanese but culturally comparable to European Canadians.

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The Asian Canadian students responded very much like their European Canadian counterparts. As a group, they slept about the same number of hours per day (seven) and had similar beliefs about the association between the amount of sleep and physical health.

So, what exactly is the relationship between sleep duration and health? It seems the relationship is moderated by one’s beliefs and cultural background. If you’ve been raised to believe that one needs eight hours a night to stay healthy, you should probably get eight hours a night. But if you’ve been raised to believe that six or seven hours is enough and sleep duration isn’t strongly associated with physical health, then by all means—work more and sleep less.