There is no ideal amount of sleep
- World Half Full
- Jun 18
- 3 min read
Updated: 8 hours ago
LIFESTYLE/HEALTH
In Japan, late nights are a way of life. The final trains of the night are often packed with people travelling home in the wee hours from work or a night out. In fact, studies consistently show that people living in Japan get far fewer winks per night than people living in other parts of the world. And yet, the Japanese enjoy the longest average lifespan of any of the world’s most economically advanced countries.
This presents a paradox. Sleep research has consistently shown that people who sleep fewer hours suffer poorer health and have shorter lives. So how can Japanese people sleep so little and still seem to thrive into old age?
Christine Ou, an assistant professor at the University of Victoria School of Nursing in Canada, together with husband Steven Heine, a professor of cultural psychology at the University of British Columbia, decided to look into how culturally distinct differences in hours of sleep affect health. So they studied 5,000 people from 20 different countries and asked, “Is there a universal amount of sleep that’s healthiest for everyone, or does that ideal vary by country?And do people feel healthier when their sleep matches what’s typical or expected of a culture?”
It turns out eight hours’ sleep is not the magic number. Sleep time varies widely from 6 hours and 18 minutes a night for Japan to 7 hours and 52 minutes a night for France; Australia is towards the high end at about 7 hours and 30 minutes hours a night.
But when Ou and Heine looked at the relationship between individuals’ health and their sleep habits, controlling for factors such as smoking and nutrition, they found the amount of sleep needed for optimal health was lower for people from countries with shorter average sleep times. They also found that people from countries that slept fewer hours on average didn’t have shorter lifespans, nor higher rates of heart disease or diabetes. These short-sleeping cultures actually had lower rates of obesity than people living in countries with longer average sleep times.
“This suggests we are learning how to sleep from our culture, and that is shaping the processes of our sleep,” says Heine.
The researchers also found that people were healthier if their sleep habits closely matched the norms of where they were living than if they diverged. This aligns with other research, they say, that shows when people fit in culturally with others where they are living — in what they eat or how they show emotions — their health is better overall.
It’s not just a matter of genetics. The behaviour, and the physiological response to it, may well be learned, they suggest. Having a sleep schedule that’s aligned with that of others in one’s community could help reduce stress related to scheduling, they suggest. “Our basic physiological needs are shaped by how we interact with our cultures,” says Ou.
A person’s needs can also shift when they move to a new area with a distinct culture. An earlier study showed university students in Japan slept an hour less than university students in Canada — but still felt less sleepy and had better health — while East Asian Canadian students had sleep behaviours and attitudes that were more similar to those of European Canadians.
Heine says the findings hit on a broader phenomenon. “The way we get our sleep needs met is shaped by cultural learning,” he says. “There’s no single ideal amount of sleep that’s best for everyone. So you can’t use eight hours as a magic number.”
The team is next planning to look into variations in the different sleep stages people go through over the course of a night — such as deep sleep versus lighter sleep. For example, Heine wonders if cultures that sleep fewer hours may enter deep sleep faster than others and speculates that “French people probably are spending more time in some of the lighter stages of sleep than, say, Japanese people.”
The research was published in the journal PNAS in May.
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