MORE THAN HALF OF TEENS ARE SLEEPING LESS HOURS NOWADAYS

The findings are from the University of Michigan's annual 'Monitoring the Future' national surveys of youth behaviour, which involved nearly 300,000 teenagers questioned between 1991 and 2012.

The results, published today in the journal Pediatrics, showed more than half the 15- to 19-year-olds surveyed in 2012 said they didn't even get seven hours each night, far less than the 10 hours experts recommend.

Declines in nightly sleep were seen in youths of all ages during the two decades, but the biggest drop was among 15-year-olds. Just over half the respondents this age reported at least seven hours nightly in 1991, versus less than 43 percent in 2012.

Also, about 30 percent of 15-year-olds reported getting what they considered enough sleep in 1991, versus 24 percent in 2012. Reports were slightly better for younger teens and worse for the oldest teens.

In most surveys, girls and non-whites were the least likely to report seven hours of sleep.

Reasons for the trend are uncertain but lead author Katherine Keyes, a Columbia University public health researcher, said factors that might have contributed include increasing use of social media, smartphones and other electronics, and rising rates of obesity, which has been linked with sleep deprivation.

Another research has suggested that early school start times play a role and advocates have been pushing for later times for teens.

Kids who don't get enough sleep are at risk for mood problems, depression, memory and learning difficulties and poor grades, said psychologist Daniel Lewin, a sleep specialist at Children's National Medical Center in Washington, D.C.

He said about 40 per cent of U.S. high schools start classes before 8 a.m. — early morning hours that are teens' 'optimal sleep period.'

The researchers say improving teens' understanding of how much sleep they need, and the consequence of not getting enough, could help.

They also say reversing the trend will require public health efforts to raise awareness about the importance of sleep for teens.

Read more: dailymail