Study investigator Dr. Dorit Koren, a pediatric endocrinologist at The Children's Hospital of Philadelphia, said the study involved 62 obese adolescents with a mean age of 14 at The Children's Hospital of Philadelphia.
The study participants -- white, African-American and Hispanic teenagers -- underwent glucose testing and an overnight sleep study. In addition to measuring total sleep time, the scientists studied "sleep architecture," analyzing stages of sleep such as slow-wave "deep" sleep and rapid eye movement (dream) sleep. The optimal sleep duration was neither too little nor too much -- both insufficient and excessive sleep were linked to higher glucose levels, Koren said.
While sleep stages did not predict glucose levels, lower duration of N3 -- "deep" sleep -- correlated with decreased insulin secretion, the researchers said.
"We already know that three out of four high school students report getting insufficient sleep," Koren said in a statement. "Our study found to keep glucose levels stable, the optimal amount of sleep for teenagers is 7.5 to 8.5 hours per night."
That is consistent with research in adults showing an association between sleep deprivation and increased risk of type 2 diabetes, Koren said.
The study was published online in the journal Diabetes Care.