It doesn’t matter whether you get eight hours of sleep or six and a half – as long as that’s normal for where you live. At least, that’s according to a new study by researchers at the University of Victoria and the University of British Columbia, in Canada.
The paper argues that cultural norms shape your sleep needs, so recommendations should be tailored to each country – rather than following a universal eight-hour rule.
“Sleep is shaped by more than just biology – it’s influenced by culture, work schedules, climate, light exposure, social norms and other factors,” lead author Dr Christine Ou, an assistant professor at Victoria’s School of Nursing, told BBC Science Focus. “What’s considered ‘enough’ sleep in one country might feel too much or not enough in another.”
Ou’s team analysed sleep habits and health data from nearly 5,000 people who completed an online questionnaire in 20 different countries across North America, South America, Europe, Asia and Africa.
Using this alongside additional data from 14 previous studies, the scientists analysed whether life expectancy and rates of heart disease, obesity and diabetes were linked to how long people slept.
They discovered that the amount of sleep the participants were getting varied widely across the 20 countries. At the top were the French participants, who slept for an average of seven hours and 52 minutes the night before filling out the questionnaire. The shortest sleepers, meanwhile, were in Japan, where participants had slept an average of just six hours and 18 minutes.
The worldwide average was seven hours and 15 minutes. In the UK, respondents slept for seven hours and 33 minutes; in the United States, for seven hours and two minutes.
Ou’s team also made a surprising discovery: there was no ‘ideal’ amount of sleep across all the countries that led to good health. In other words, her team found no evidence that people in countries with shorter average sleep durations had worse health as a result, compared to individuals in countries where people slept for longer each night.
One answer was common across the board, though. Participants were asked what they thought was the optimum sleep hours for good health was – in Costa Rica, for example, this averaged at eight hours and three minutes, whereas it was just seven hours and 16 minutes in South Korea. And, in every country, most participants felt they were between were one hour and an hour and 40 minutes short of this target.
Yet those whose sleeping hours were closest to their country's optimum were most likely to be in good health. In other words, if you're in the US and you're sleeping for around seven hours and two minutes every night, you're more likely to be healthy.
“Our study found that people tend to be healthier when their sleep aligns with what’s typical in their culture," said Ou. “Recognising cultural context can help people focus on what actually supports their health, rather than chasing a fixed number.”
Within each country, the scientists found that deviating too much from the cultural sleep norm was associated with worse health outcomes – whether that meant getting too little sleep or too much.
The point at which too much sleep started to lead to worse health outcomes also varied. This point was highest in the UK, where participants getting over 10 hours and 26 minutes of sleep started to lose the health benefits of getting enough sleep. The lowest, meanwhile, was in the US, where participants could only slumber for eight hours and 13 minutes before this started to happen.
Sleep psychologist Dr Daljinder Chalmers, of Keele University, told BBC Science Focus: “Sleep is really complex, and there’s no evidence to support the idea that we should all sleep for eight hours per day.”
Chalmers, who was not involved with this research, added that in countries where people sleep less during the night they may be napping more during the day, or they may just need less sleep.
She said: “When you’re looking at sleep and health, you need to consider culture.”
The researchers behind the study controlled for factors like the nutrition, wealth, inequality and geography of each country – but this was still only an observational study, so they couldn't make conclusions about the direct effect that sleep had on participants' health.
Read more:
- The 8 science-backed secrets to a more restful night's sleep
- How hidden 'overtiredness' is ruining your sleep – and how to fix it
- Always tired? A fixed bedtime matters more than sleep duration, study finds
About our experts
Dr Christine Ou is an assistant professor at the University of Victoria's School of Nursing, in Canada. Having begun her career as a paediatric registered nurse, she continues to support children and families with a programme of research focused on the sleep and psychosocial wellbeing of families with infants and children. Ou is an active Canadian Perinatal Mental Health Collaborative national committee member and has been recognised as a University of British Columbia Public Scholar and Applied Sciences Rising Star.
Dr Daljinder Chalmers is a lecturer in health psychology at Keele University, specialising in sleep. She has extensive experience working in academia, the civil service and the NHS. Chalmers gained her BSc in psychology from Bedfordshire University, her MSc in health psychology from Derby University and her PhD from Portsmouth University.
