US universities have been given an explanation for students' tendency to seem tired all the time - it's not because they stay up too late but because classes start too early.
The news has moved at least one institution to start morning classes later and has ignited a nationwide debate about whether students are being overworked or coddled.
Duke University has announced that its morning classes will no long start at 8am but at 8.30am or 8.45am. The shift comes as a committee of campus counsellors at Duke warned about lack of sleep and its effect on students'
health and proposed a university-wide "wellness" campaign.
But Duke now says that its concerns about students' lack of sleep and the change in the starting time of morning classes are not related. It blamed the media for misrepresenting the situation.
"Both initiatives are important and should benefit our students, but linking the two together is just not correct," said Judith Ruderman, Duke's vice-provost. "I'm ready for my phone to stop ringing."
Researchers told a recent conference at the University of Michigan that US university students were sleeping an average of six to seven hours a night, down from seven to seven and a half hours a night 20 years ago.
They said the right amount of sleep for people of university age was nine hours a night, and they concluded that sleep deprivation was hurting academic performance and contributing to stress.
The Comprehensive Sleep Disorders Center at Rutgers University goes even further, recommending that students get as much as nine and a half hours of sleep a night. It suggested that less than that could lead to "delayed sleep-phase syndrome", a glitch in the body's biological clock.
There is also growing concern that students are keeping themselves awake longer with not only traditional aids such as caffeine but with prescription drugs meant to treat attention-deficit disorder.
Johns Hopkins University reports that one in five students uses prescription drugs, and a national anti-drug organisation estimates that nearly one in ten, or 2.1 million, university-aged Americans has taken Ritalin or similar drugs without a prescription.
But students and others have dismissed the findings. A large proportion of students, rather than working too hard, avoid morning courses altogether, enrolment patterns show.
Universities have also raised alarms about students forgoing any Friday classes so as to extend their weekends.