A new study finds, that our internal biological clocks may not exactly determine when we go to sleep but they affect when we wake up in the morning.
The biological clock, sometimes called the circadian clock, has been thought to be the primary driver of human sleep schedules and is affected by environmental cues, such as sunlight. The new findings show that “bedtime is more under the control of society, and wake time is more under the control of the [biological] clock,” Olivia Walch, a graduate student at the University of Michigan and a co-author of the study said.
In the study conducted, more than 8,000 people in 100 countries were used by researchers to collect sleep data through a smartphone app that helps travelers adjust to new time zones. To use the app, you enter your typical sleep schedule, as well as the times when you are normally exposed to light. Using this information, the app suggests custom schedules of light and darkness to help you adjust to a new time zone. In other words, the app suggests that you be exposed to bright light at one point during the day and to darkness at another point.
Singapore and Japan were found to have the least amount of sleep, with an average of about 7 hours and 24 minutes per night, whereas people in the Netherlands got the most sleep, with 8 hours and 12 minutes, on average.
Though the difference in average sleep duration between these countries may not seem huge, every half-hour of sleep can greatly affect people’s cognitive function and long-term health, the researchers said.
The researchers saw that countries that are geographically and culturally close to each other, such as Japan and Singapore, tended to have similar sleep patterns.
The researchers also looked at how sleep times varied among people of different ages and between genders. They found that middle-age men got the least sleep — often less than the recommended 7 to 8 hours per night, according to the study.
When the researchers compared sleep times in the men versus the women, they found that the women in the study scheduled 30 minutes more sleep than men per night, on average. Women went to bed earlier and woke up later than men, the study found.
Moreover, the researchers found that people’s sleep schedules seemed to become more similar to the habits of their peers as they got older. For example, there were more similarities among the sleep schedules of people older than 55, compared with those younger than 30. One possible explanation for this is that older people tend to have a narrower window of time within which they can fall and stay asleep, according to the study.
The new findings are a reminder that sleep is more important than many people may realize, the researchers said. Even if someone is getting 6 hours of sleep per night, which is less than the recommended 7 to 8 hours, that person is still building up a sleep debt, Walch said in a statement. Sleep debt is the effect that sleep deficiency has on the body, which may lead to physical and mental fatigue. “It doesn’t take that many days of not getting enough sleep before you’re functionally drunk,” she said.