College students who regularly get a good night’s sleep are more likely to have better grades, according to a small but intriguing study by researchers at the Massachusetts Institute of Technology (MIT).
The study is intriguing because it didn’t start out as research on sleep. It was designed instead to see what impact physical exercise has on academic performance.
But to the surprise of its authors, lack of sleep, not lack of exercise, emerged as the stronger predictor of students’ grades.
“What we found at the end of the day was zero correlation with fitness, which I must say was disappointing since I believed, and still believe, there is a tremendous positive impact of exercise on cognitive performance,” says Jeffrey Grossman, the study’s senior author and a professor of environmental systems at MIT, in a released statement.
The study was published online Tuesday in the journal Science of Learning.
A more objective measuring tool
Sleep is, of course, crucial for good cognitive function. In addition to enabling us to think clearly and make decisions, sleep consolidates our memories — a task essential for helping college students (and the rest of us) remember newly learned information.
Plenty of previous research has looked at — and found — an association between sleep and academic performance, but most of those studies relied on sleep diaries filled out by the students themselves. In this new study, Grossman and his colleagues had 100 students wear fitness trackers, which offer a more objective way of tracking the duration and timing of sleep.
The students, 43 men and 47 women, were in one of Grossman’s introductory chemistry classes and volunteered for the study. They were each given a fitness tracker and asked to wear it throughout the 14-week semester. Eighty-eight of them followed the instructions fully and completed the study.
As already noted, the initial intention of having the students wear the trackers was to record their physical activity and see if that activity was linked to their grades in the course. No such association was found. When the researchers looked at the sleep data on the trackers, however, they did find strong correlations with grades — ones that Grossman says were not at all subtle.
Three key measures
The students who got the most sleep, the better quality sleep and the most consistent sleep tended to receive overall better grades in chemistry class than those who got the least sleep. (Overall grade scores were determined by adding up the students’ scores on 11 quizzes, three midterms and a final exam.)
Together, those three sleep measures — duration, quality and consistency — accounted for about 25 percent of the variance in the student’s overall grade performance, the data revealed.
Consistency was especially important. When Grossman and his colleagues dug down into the data, they found that getting a good night’s sleep only on the night before a big test didn’t make any difference in how well the students did on that test.
“The implications of these findings are that, at least in the context of an academic assessment, the role of sleep is crucial during the time the content itself is learned, and simply getting good sleep the night before may not be as helpful,” Grossman and his colleagues write.
The study also found that there’s a cut-off bedtime for good academic performance: 2 a.m. Night owls who stayed up later than that tended to have poorer academic performances, even if their total sleep time was the same as their earlier-to-bed peers.
“When you go to bed matters,” says Grossman. “If you get a certain amount of sleep — let’s say seven hours — no matter when you get that sleep, as long as it’s before certain times, say you go to bed at 10, or at 12, or at 1, your performance is the same. But if you go to bed after 2, your performance starts to go down even if you get the same seven hours. So quantity isn’t everything.”
Quality of sleep did matter, however. The students who were relatively consistent in the amount of sleep they got each night did better in the chemistry course than students whose sleep patterns were more irregular, even if they ended up with the same average amount of sleep.
Gender differences also emerged from the sleep data. Women students tended to experience higher quality and more consistent sleep throughout the semester than their male counterparts.
Grossman notes that this finding may explain something he has observed for years: Women, on average, have done consistently better in his introductory chemistry course than men.
“If we correct for sleep, men and women do the same in class. So sleep could be the explanation for the gender difference in our class,” he says.
Limitations and implications
The study was small and involved young people in one class at one university. The findings may not be applicable to broader, more diverse groups of students.
In addition, as Grossman and his colleagues point out, the relationship between sleep and academic performance may be moderated by factors that affect sleep, such as stress, anxiety, motivation, personality traits and gender roles. Those factors weren’t adjusted for in this study.
And finally — and, perhaps, most importantly — this study is observational, which means it can’t prove cause and effect.
Still, the findings are interesting and certainly in line with other research on this topic. As Grossman says, the study offers yet another strong indication that, when it comes to academic performance, sleep “really, really matters.”
FMI: You can read the study in full on the Science of Learning website.