How sleep patterns differ by sex, age and country revealed by app

Smartphone app data hint at how societal pressures to sacrifice sleep contribute to a "global sleep crisis," a new study suggests.

Researchers created a free, no-ad app to fight jetlag, and asked people aged 15 and older to send them a treasure trove of anonymous sleep, wake-up and lighting data. Now the mathematicians and computational medicine experts have explored how cultural pressures can override our natural circadian rhythms at bedtime.

"It is middle-aged men that seem to be getting a remarkably little amount of sleep, and we think that is very significant," the study's lead author, math Prof. Daniel Forger of the University of Michigan in Ann Arbor, said in an interview. "They are behind the wheel driving trucks, driving airplanes and when they do it with so little sleep, that can pose risks to themselves and also to society."

In Friday's issue of the journal Science Advances, Forger and colleagues Olivia Walch and Amy Cochran analyzed data from about 6,000 people in more than 100 countries. Their findings included:

• Middle-aged men often get less than the recommended seven to eight hours of shut-eye.
• Women schedule about 30 more minutes of sleep on average by going to bed earlier and waking up later.
• Age is the main driver of sleep timing. Sleep schedules were more similar among those 55 and older than those younger than 30. As people get closer to retirement, the researchers suspect our bodies will only let us sleep at certain times of the day, Forger said.

"If you have very little sleep, you can perform just as well as when you are drunk, so not getting much sleep is indeed a global crisis right now," he said, based on previous studies.

What's "normal" for one country differs, the researchers found. The data showed Canadians tend to wake up after 7 a.m., a sleep pattern more similar to those in Britain than in the U.S., Forger said. For total sleep time, Canadians averaged more than 7.9 hours. 

'Bad habits' blamed

Jason Coulls of Toronto said he averages six hours a night, but would ideally like seven to 7.5 hours.

"Between kids, bad habits such as staying up on the iPad, looking at Facebook too much, all those types of things," he said of why he doesn't get the amount of sleep he wants.

Carol LeFleur said she mostly gets enough sleep, about seven hours. "I try as much as possible to get enough sleep so I can go through the day without feeling stressed out."

Pat Hastings said she tends to get eight hours a day, but sometimes has trouble getting to sleep or waking up in the middle of the night.

Not sleeping well can affect what she does the next day, such as trying to catch up on sleep as a passenger. "My husband drives [us] down to the subway station and I get to sleep."

The researchers found the Dutch reported the most sleep at about 8.1 hours.

Those in Japan and Singapore reported the least hours of sleep, about 7.5 hours. 

In Japan, subway commuters often sleep on the train and feel safe doing so, said Dr. Jun Kohyama, a CEO of Tokyo Bay Urayasu/Ichikawa Medical Center and an expert on sleep.

"They have to nap because they are very, very sleep deprived," Kohyama said.

Japanese people may be irritable from lack of sleep, and workers often retire early because of depression and mood disorders, he said.

"Sleep loss leads to a decrease in function of the brain's prefrontal cortex," which is responsible for logical thinking, Kohyama said. He speculates that the effects of lack of sleep on logical thinking could then spiral into an inability to change lifestyle.

The study's authors plan to release a version of the Entrain app to collect sleep quality data as well so they can further explore why people sleep differently.

While sleep labs remain the gold standard in research, Forger estimates it would have cost more than $200 million U.S. to do the same experiment that way compared with almost no cost to develop the app.  

The study was funded by the U.S. Army Research Laboratory, the Air Force Office of Scientific Research and the National Science Foundation.