Better sleep habits lead to better college grades

Data on MIT students underscore the importance of getting enough sleep; bedtime also matters

October 1, 2019

Science Daily/Massachusetts Institute of Technology

Two MIT professors have found a strong relationship between students' grades and how much sleep they're getting. What time students go to bed and the consistency of their sleep habits also make a big difference. And no, getting a good night's sleep just before a big test is not good enough -- it takes several nights in a row of good sleep to make a difference.

Those are among the conclusions from an experiment in which 100 students in an MIT engineering class were given Fitbits, the popular wrist-worn devices that track a person's activity 24/7, in exchange for the researchers' access to a semester's worth of their activity data. The findings -- some unsurprising, but some quite unexpected -- are reported today in the journal Science of Learning in a paper by MIT postdoc Kana Okano, professors Jeffrey Grossman and John Gabrieli, and two others.

One of the surprises was that individuals who went to bed after some particular threshold time -- for these students, that tended to be 2 a.m., but it varied from one person to another -- tended to perform less well on their tests no matter how much total sleep they ended up getting.

The study didn't start out as research on sleep at all. Instead, Grossman was trying to find a correlation between physical exercise and the academic performance of students in his class 3.091 (Introduction to Solid-State Chemistry). In addition to having 100 of the students wear Fitbits for the semester, he also enrolled about one-fourth of them in an intense fitness class in MIT's Department of Athletics, Physical Education, and Recreation, with the help of assistant professors Carrie Moore and Matthew Breen, who created the class specifically for this study. The thinking was that there might be measurable differences in test performance between the two groups.

There wasn't. Those without the fitness classes performed just as well as those who did take them. "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," Grossman says.

He speculates that the intervals between the fitness program and the classes may have been too long to show an effect. But meanwhile, in the vast amount of data collected during the semester, some other correlations did become obvious. While the devices weren't explicitly monitoring sleep, the Fitbit program's proprietary algorithms did detect periods of sleep and changes in sleep quality, primarily based on lack of activity.

These correlations were not at all subtle, Grossman says. There was essentially a straight-line relationship between the average amount of sleep a student got and their grades on the 11 quizzes, three midterms, and final exam, with the grades ranging from A's to C's. "There's lots of scatter, it's a noisy plot, but it's a straight line," he says. The fact that there was a correlation between sleep and performance wasn't surprising, but the extent of it was, he says. Of course, this correlation can't absolutely prove that sleep was the determining factor in the students' performance, as opposed to some other influence that might have affected both sleep and grades. But the results are a strong indication, Grossman says, that sleep "really, really matters."

"Of course, we knew already that more sleep would be beneficial to classroom performance, from a number of previous studies that relied on subjective measures like self-report surveys," Grossman says. "But in this study the benefits of sleep are correlated to performance in the context of a real-life college course, and driven by large amounts of objective data collection."

The study also revealed no improvement in scores for those who made sure to get a good night's sleep right before a big test. According to the data, "the night before doesn't matter," Grossman says. "We've heard the phrase 'Get a good night's sleep, you've got a big day tomorrow.' It turns out this does not correlate at all with test performance. Instead, it's the sleep you get during the days when learning is happening that matter most."

Another surprising finding is that there appears to be a certain cutoff for bedtimes, such that going to bed later results in poorer performance, even if the total amount of sleep is the same. "When you go to bed matters," Grossman says. "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 also mattered, not just quantity. For example, those who got relatively consistent amounts of sleep each night did better than those who had greater variations from one night to the next, even if they ended up with the same average amount.

This research also helped to provide an explanation for something that Grossman says he had noticed and wondered about for years, which is that on average, the women in his class have consistently gotten better grades than the men. Now, he has a possible answer: The data show that the differences in quantity and quality of sleep can fully account for the differences in grades. "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.

More research will be needed to understand the reasons why women tend to have better sleep habits than men. "There are so many factors out there that it could be," Grossman says. "I can envision a lot of exciting follow-on studies to try to understand this result more deeply."

"The results of this study are very gratifying to me as a sleep researcher, but are terrifying to me as a parent," says Robert Stickgold, a professor of psychiatry and director of the Center for Sleep and Cognition at Harvard Medical School, who was not connected with this study. He adds, "The overall course grades for students averaging six and a half hours of sleep were down 50 percent from other students who averaged just one hour more sleep. Similarly, those who had just a half-hour more night-to-night variation in their total sleep time had grades that dropped 45 percent below others with less variation. This is huge!"

Stickgold says "a full quarter of the variation in grades was explained by these sleep parameters (including bedtime). All students need to not only be aware of these results, but to understand their implication for success in college. I can't help but believe the same is true for high school students." But he adds one caution: "That said, correlation is not the same as causation. While I have no doubt that less and more variable sleep will hurt a student's grades, it's also possible that doing poorly in classes leads to less and more variable sleep, not the other way around, or that some third factor, such as ADHD, could independently lead to poorer grades and poorer sleep."

https://www.sciencedaily.com/releases/2019/10/191001083956.htm

Teens get more sleep with later school start time

December 12, 2018

Science Daily/University of Washington

In 2016, Seattle Public Schools pushed back start times for its 18 high schools by 55 minutes. Researchers have now announced that, as a result, teens at two Seattle high schools got more sleep on school nights -- a median increase of 34 minutes of sleep each night -- and showed improved attendance and grades.

When Seattle Public Schools announced that it would reorganize school start times across the district for the fall of 2016, the massive undertaking took more than a year to deploy. Elementary schools started earlier, while most middle and all of the district's 18 high schools shifted their opening bell almost an hour later -- from 7:50 a.m. to 8:45 a.m. Parents had mixed reactions. Extracurricular activity schedules changed. School buses were redeployed.

And as hoped, teenagers used the extra time to sleep in.

In a paper published Dec. 12 in the journal Science Advances, researchers at the University of Washington and the Salk Institute for Biological Studies announced that teens at two Seattle high schools got more sleep on school nights after start times were pushed later -- a median increase of 34 minutes of sleep each night. This boosted the total amount of sleep on school nights for students from a median of six hours and 50 minutes, under the earlier start time, to seven hours and 24 minutes under the later start time.

"This study shows a significant improvement in the sleep duration of students -- all by delaying school start times so that they're more in line with the natural wake-up times of adolescents," said senior and corresponding author Horacio de la Iglesia, a UW professor of biology.

The study collected light and activity data from subjects using wrist activity monitors -- rather than relying solely on self-reported sleep patterns from subjects, as is often done in sleep studies -- to show that a later school start time benefits adolescents by letting them sleep longer each night. The study also revealed that, after the change in school start time, students did not stay up significantly later: They simply slept in longer, a behavior that scientists say is consistent with the natural biological rhythms of adolescents.

"Research to date has shown that the circadian rhythms of adolescents are simply fundamentally different from those of adults and children," said lead author Gideon Dunster, a UW doctoral student in biology.

In humans, the churnings of our circadian rhythms help our minds and bodies maintain an internal "clock" that tells us when it is time to eat, sleep, rest and work on a world that spins once on its axis approximately every 24 hours. Our genes and external cues from the environment, such as sunlight, combine to create and maintain this steady hum of activity. But the onset of puberty lengthens the circadian cycle in adolescents and also decreases the rhythm's sensitivity to light in the morning. These changes cause teens to fall asleep later each night and wake up later each morning relative to most children and adults.

"To ask a teen to be up and alert at 7:30 a.m. is like asking an adult to be active and alert at 5:30 a.m.," said de la Iglesia.

Scientists generally recommend that teenagers get eight to 10 hours of sleep each night. But early-morning social obligations -- such as school start times -- force adolescents to either shift their entire sleep schedule earlier on school nights or truncate it. Certain light-emitting devices -- such as smartphones, computers and even lamps with blue-light LED bulbs -- can interfere with circadian rhythms in teens and adults alike, delaying the onset of sleep, de la Iglesia said. According to a survey of youth released in 2017 by the U.S. Centers for Disease Control and Prevention, only one-quarter of high school age adolescents reported sleeping the minimum recommended eight hours each night.

"All of the studies of adolescent sleep patterns in the United States are showing that the time at which teens generally fall asleep is biologically determined -- but the time at which they wake up is socially determined," said Dunster. "This has severe consequences for health and well-being, because disrupted circadian rhythms can adversely affect digestion, heart rate, body temperature, immune system function, attention span and mental health."

The UW study compared the sleep behaviors of two separate groups of sophomores, all enrolled in biology classes at Roosevelt and Franklin high schools. One group of 92 students, drawn from both schools, wore wrist activity monitors all day for two-week periods in the spring of 2016, when school still started at 7:50 a.m. The wrist monitors collected information about light and activity levels every 15 seconds, but no physiological data about the students. In 2017, about seven months after school start times had shifted later, the researchers had a second group of 88 students -- again drawn from both schools -- wear the wrist activity monitors. Researchers used both the light and motion data in the wrist monitors to determine when the students were awake and asleep. Two teachers at Roosevelt and one at Franklin worked with the UW researchers to carry out the study, which was incorporated into the curriculum of the biology classes. Students in both groups also self-reported their sleep data.

The information obtained from the wrist monitors revealed the significant increase in sleep duration, due largely to the effect of sleeping in more on weekdays.

"Thirty-four minutes of extra sleep each night is a huge impact to see from a single intervention," said de la Iglesia.

The study also revealed other changes beyond additional shut-eye. After the change, the wake-up times for students on weekdays and weekends moved closer together. And their academic performance, at least in the biology course, improved: Final grades were 4.5 percent higher for students who took the class after school start times were pushed back compared with students who took the class when school started earlier. In addition, the number of tardies and first-period absences at Franklin dropped to levels similar to those of Roosevelt students, which showed no difference between pre- and post-change.

The researchers hope that their study will help inform ongoing discussions in education circles about school start times. The American Academy of Pediatrics recommended in 2014 that middle and high schools begin instruction no earlier than 8:30 a.m., though most U.S. high schools start the day before then. In 2018, California lawmakers nearly enacted a measure that would ban most high schools from starting class before 8:30 a.m. In 2019, Virginia Beach, home to one of the largest school districts in Virginia, will consider changes to its school start times.

https://www.sciencedaily.com/releases/2018/12/181212140741.htm