BEIJING, Feb. 21 (Xinhuanet) -- How much sleep do teenagers need? The more, the better? Not really.

Researchers from Brigham Young University found that seven-hour sleepers do better academically than their 9-hour counterparts, even though guidelines recommend nine.

This study was published in The Eastern Economics Journal.

Eric Eide and economics professor Mark Showalter aim to determine what impact sleep duration and quality might have on people's education and health. This study report is the first in a series.

They gathered data on 1,724 primary and secondary pupils across the United States. They believed that theirs was a nationally representative sample of schoolchildren.

"We're not talking about sleep deprivation. The data simply says that seven hours is optimal at that age," said Eric Eide.

Apparently, test performance results depend on several factors, but as far as sleep is concerned, more does not necessarily mean better.

The study found that sleep schoolchildren require drops with age:

· 10-year olds. The optimal amount is 9-9.5 hours each night

· 12-year-olds. The optimal amount is 8-8.5 hours each night

· 16-year-olds. The optimal amount is 7 hours each night