A child sleeps on the shoulder of a woman in Jinan, capital of east China's Shandong Province, March 16, 2015. March 21 is the 15th World Sleep Day. (Xinhua/Guo Xulei)
Social pressure is forcing people to sleep less than needed, contributing to a "global sleep crisis," scientists said in a new study based on data collected from a smartphone app.
Researchers from the University of Michigan have tracked sleep patterns of some 6,000 people in 100 countries and analyzed connections with age, gender, daily natural light exposure as well as cultural pressures.
"The effects of society on sleep remain largely unquantified," said the study published Friday in the journal Science Advances.
"We find that social pressures weaken and/or conceal biological drives in the evening, leading individuals to delay their bedtime and shorten their sleep."
Lack of sleep is mostly affected by the time people go to bed, the study found.
Middle-aged men get the least amount of sleep, less than the recommended seven to eight hours. And age is the main factor determining the amount of sleep.
The research is based on data collected through the free smartphone app Entrain, launched in 2014 to help users fight jetlag.
Sleep is driven by an internal "circadian" clock, a cluster of 20,000 nerve cells the size of a grain of rice located behind the eyes, and adjusted according to the amount of light captured, especially natural light.
People in Singapore and Japan have the least amount of sleep -- with an average amount of seven hours 24 minutes, while those in Netherlands have the most with an average of eight hours 12 minutes of sleep, the study found.
Although a difference of 48 minutes may seem inconsequential, a lack of sleep for half an hour can have significant effects on cognitive function and health, the researchers said.
"Impaired sleep presents an immediate and pressing threat to human health," the study said.
