Scientists warn of 'global sleep crisis'

Social pressures are forcing people to cut back on their sleep, contributing to a "global sleep crisis," according to a new study based on research collected through a smartphone app named Entrain.

It enabled scientists from the University of Michigan to track sleep patterns around the world -- gathering data about how age, gender and the amount of natural light to which people are exposed affect sleep patterns in 100 countries -- and better understand how cultural pressures can override biological rhythms.

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.

The average amount of sleep in the world varies from a minimum of seven hours 24 minutes in Singapore and Japan to a maximum of eight hours 12 minutes in the Netherlands, 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. People who need sleep suffer a reduction in their cognitive abilities without really being conscious of it, the new study says.