Researchers at Brigham Young University in Provo surveyed 184 of the school's freshmen and found that the later students slept in the morning, the lower their grades tended to be.

Out of all the factors studied, weekday and weekend wakeup times had the strongest association with students' GPAs. Each hour over the average that students slept in on weekdays was associated with a 0.13-point drop on the GPA (0.0-4.0 scale). A similar correlation was found for hours spent in bed on weekends, when many students catch up on sleep.

Eating breakfast each morning was also associated with higher grades, while having a night job was associated with lower grades.

Although many would automatically assume that alcohol consumption was a possible culprit for the connection between late sleeping and poor grades, since heavy drinking has been shown to damage academic performance. But the researchers point out that Brigham Young University is a dry campus where students sign agreements not to drink. "Alcohol-consumption behavior sufficient to cause morning hangover would be difficult to hide in the monitored residence halls of this university," the authors wrote in the report.

Journal of American College Health 2000; 49: 125-130