Smartphones show us how the world sleeps

A study, led by University of Michigan mathematicians, used a free smartphone application that reduces jet lag to collect reliable sleep data from thousands of people in 100 different countries. The study of worldwide sleep patterns combines math modeling, mobile applications and huge data to analyze the effects of biology and society on how a person sleeps. The researchers examined how age, gender, amount of light and home country affect the amount of shut-eye people around the globe get, what time they go to bed, and when they wake up.

The study revealed that women aged 30-60 worldwide are sleeping more than men, about 30 minutes more on average. Middle aged men are the ones getting the least sleep and are quite often getting less than the recommended 7-8 hours of daily sleep. The smartphone application based study also showed that people who are getting some exposure to sunlight on a daily basis get more sleep and tend to go to bed earlier than the ones who spend most of their time indoors.

Across the board, it appears that society governs bedtime and one’s internal clock governs wake time, and a later bedtime is linked to a loss of sleep,” said Daniel Forger, a faculty member of the mathematics department at the University of Michigan College of Literature, Science, and the Arts, and in the Medical School’s Department of Computational Medicine and Bioinformatics. “At the same time, we found a strong wake-time effect from users’ biological clocks–not just their alarm clocks. These findings help to quantify the tug-of-war between solar and social timekeeping.”

Sleep is more important than a lot of people realize. Even if you get six hours a night, you’re still building up a sleep debt,” said Olivia Walch, a doctoral student in the mathematics department. “It doesn’t take that many days of not getting enough sleep before you’re functionally drunk,” Walch noted, adding that the researchers have figured out that being overly tired can have that effect. What is terrifying at the same time is that people think they are performing tasks way better than they are despite less sleep. “Your performance drops off but your perception of your performance doesn’t,” the authors emphasized.

Our internal and biological clocks are circadian rhythms, that are fluctuations in bodily functions and behaviors that are tied to the planet’s 24-hour day and cultural pressures can alter our natural circadian rhythms, with the effects most noticeable at bedtime. Even though morning responsibilities like work, kids and school play a role in wake-time, the researchers say these are not the only factor that affect our sleep cycles. These circadian rhythms are regulated by a rice grain sized cluster of some 20,000 neurons behind the eyes and are set by the amount of light, especially sunlight, that our eyes take in.

National averages of sleep duration ranged from a minimum of around 7 hours and 24 minutes of sleep for residents of Singapore and Japan to a maximum of 8 hours and 12 minutes for those living in the Netherlands. It’s not a huge window, but the researchers state that every half hour of sleep makes a big difference in terms of cognitive function and long-term health.

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