The study by lead author Pamela Thacher at St. Lawrence University in Canton, N.Y., and co-author Serge Onyper found not only did later class start times predict more drinking and sleeping, but also modestly lower grades, overall.
"Later class start times seemed to change the choices students make: They sleep longer, and they drink more," Thacher says in a statement.
Thacher and Onyper say their study involved 253 college students who completed cognitive tasks and a one-week retrospective sleep diary, as well as questionnaires about sleep, class schedules, substance use and mood.
"The effects of later class start times might include more sleep," Thacher says. "But this might be offset by lower quality sleep, which in turn might affect their ability to engage, intellectually, with their coursework."
Thacher speculated drinking more alcohol, known to disrupt sleep, may reduce the benefits of getting more sleep.
The 25th Anniversary Meeting of the Associated Professional Sleep Societies LLC in Minneapolis.