Seven hours of sleep a day enough for teens: Study

London: Want to do well at school? Then, cut down on your lie-ins, as teenagers do not need more than seven hours of sleep a day, scientists say.

A team at the Brigham Young University in Utah found that teenagers performed better academically if they had more regular sleep patterns limited to just seven hours.

It`s believed that a typical 16-year-old needs nine hours of sleep a night, but the optimum amount is just seven hours, said lead study author Eric Eide.

"We are not talking about sleep deprivation. The data simply says that seven hours is optimal at that age," Eide is quoted as saying by the Daily Mail.

The researchers said the right amount of sleep decreases with age, while the optimum amount of sleep for a ten-year-old is around nine hours, it is eight hours for 12-year-olds.

For their study, published in the Eastern Economics Journal, the researchers looked at 1,724 primary and secondary school students across the US, assessing how much sleep they got and how they scored in standardised tests.

The impact of sleep on test scores depended on a number of factors, such as how educated the child`s parents were.

"Most of our students at BYU, especially those that took early-morning seminary classes in high school, are going to realise that nine hours of sleep isn`t what the top students do," said study co-author Mark Showalter.

A University of Chicago study, published in the Journal of the American Medical Association, had found those who sleep for less than five hours a night for periods of longer than a week have significantly lower levels of testosterone than those who get a full night`s rest.

And with testosterone affecting men`s libido and energy levels, the researchers pointed out that those who miss out on sleep are much more likely to be put off sex. The affect is so drastic it reduces the hormone to levels more akin to someone 15 years older, they had noted.

Another of thousands of women had found significantly fewer cases of cancer, including breast cancer, among those who were the most physically active. But sleeping less than
seven hours a night wiped out the benefits of exercise and increased the risk of cancer, it had found.