Better quality of sleep is strongly associated with better academic performance in college


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.”

Even relatively small differences in the duration, timing, and consistency of students’ sleep may have significant effects on course test results, a new MIT study shows.

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 team also included technical assistant Jakub Kaezmarzyk and Harvard Business School researcher Neha Dave.

Funding: The study was supported by MIT’s Department of Materials Science and Engineering, the Lubin Fund, and the MIT Integrated Learning Initiative.

Physiologic and cognitive function in humans varies considerably during the day along the circadian rhythm. The sleep and wakefulness cycle is extensively regulated through intrinsic neural mechanisms (e.g., suprachiasmatic nucleus) [1].

However, the timing and expression of sleep and wakefulness are highly influenced by environmental factors [2]. Sleep deprivation of varying occasions and durations can substantially impair physical, cognitive, and emotional functions.

Medical students and house medical staff work for long hours daily, and this continuous shifting without recuperation time has raised concerns about the severe effects of poor sleep quality in student training, medical errors, and patient safety [2].

Many factors alter sleep habits including coffee and tea intake, overuse of the internet and other social media, and the use of sleep medications.

Furthermore, various medical problems profoundly disrupt sleep, including obstructive sleep apnea, depression, chronic sleep deprivation, narcolepsy, cataplexy, and idiopathic hypersomnia [34].

While these various factors all contribute to sleep quality, the relationship of the academic achievement to sleep habits is a key issue, especially for medical students [2]. Poor sleep quality has been associated with reduced academic achievement [5], and sleep quality has also been reported to be related to negative effects on health, emotional feelings and well-being in college students [6].

Sleep quality affect medical student physical, mental health, and working capacity [7], which in turn influence the community in the form of accidents and medical error. No data are currently available regarding the effect of sleep quality on medical student performance in Sudan.

Sudan is one of the largest countries in Africa, taking about 2 % of the earth’s surface, so the previous studies may not generalize to Sudan, due to environmental conditions, social conditions, and school environment.

Therefore, we conducted the current study to understand the sleep habits of Sudanese medical students and whether they like those in Western countries had poor sleep quality.

In the current study, we examined the relationship between the sleep quality and academic performance among medical students by comparing groups with different levels of academic performance. Measures to improve both living condition and sleep quality are recommended.

Subjects and methods

Study design

This case–control study based on academic performance was conducted at two universities (University of Omdurman and Bahri) in Khartoum, Sudan.


This study aimed to encompass all the students in the fifth and sixth classes who score A (excellent) and C (pass) in the previous semester (they were selected from the total number of 300 medical students registered for these classes), those with score B (good) and score D (fail) were excluded from the study. One hundred sixty-five, medical students responded to the questionnaire, response rate 81.6 % (165/202). Twenty-five medical students who did not record their grades were also excluded. School performance was stratified as A, (excellent), B (good), C (pass), and D (fail).

An orientation meeting was arranged with the participants, and they were orally briefed by two of the researchers (HM, and MA) about the research objectives and how to fill the questionnaire. Group leaders from all the semesters helped to distribute the questionnaire. Participation was voluntary and unpaid. All the participants signed a written informed consent form.

Subjects were asked to maintain a diary documenting sleep and wake times for 2 weeks and then they completed the Pittsburgh Sleep Quality Index (PSQI). This instrument has been previously validated for college students in sub-Saharan Africa [8] and was shown to be consistent with objective measures [9].

The PSQI contains seven components, each with a score from 0 to 3 with 3 indicating the greatest dysfunction. The global sleep quality score ranged from 0 to 21, and candidates with PSQI of more than 5 were labeled as having poor sleep quality, and those with PSQI of less than or equal 5 as good sleep quality [10].

The PSQI ( measures sleep-related habits in the past month including sleep latency, sleep duration, sleep efficiency, sleep disturbance, subjective sleep quality, daytime dysfunction, and sleep medication use. Sleep efficiency is the ratio of time spent in sleep (total sleep time) to the amount of time spent in bed.

The bedtime delay is the (weekday bedtime-weekends bedtime), and wake-up time delay is the (wake-up time during weekdays-wake-up time during weekends) A sleep time difference of more than an hour between weekdays and weekends was considered irregular bedtime [11].

Data were collected at times other than examination days to avoid stress during the preparation for exams. Approval for the study was provided by the ethical committees of Omdurman and Bahri Universities.

Statistical analysis

Data were analyzed by using statistical software (SPSS version 20), Descriptive statistics was reported as means and frequencies ANOVA was used for testing the significant difference between study groups. The results were considered statistically significant when p ≤ 0.05.


165 medical students were enrolled in the study, and 25 incomplete questionnaires were not included. The two groups consisted of 65 excellent (A) and 75 average (C) grade students.

Out of 140 medical students, female dominance was evident: (72.4 %) among the excellent group, and 73.3 % among the average group, with no statistical difference between the two groups (P = 0.73). Bad sleep quality was detected in 24 (36 %) of the excellent group, and 71 (94.6 %) of the passing group, with a significant difference seen between groups (p < 0.001). Bedtime later than midnight was detected in 55.3 % in the excellent group and 85.3 % in the average group with statistical significant difference between the two groups (p < 0.001), other student’s characteristics are shown in Table 1. Table 2 illustrates sleep characteristics from the PSQI for the two groups in which, the mean age was 22.5 ± 1.8 for the excellent group and 22.6 ± 1.9 for the average group with no statistical difference between the groups (P = 0.823). The overall sleep quality was 4.03 ± 3.3 for the excellent group and 10.6 ± 3.8 for the average group with a significant statistical difference between the two groups (p < 0.001) and F = 118.2. The mean sleeping hours at night was 7 ± 1.9, among the excellent group, and 6.3 ± 1.9 among the average group, (p < 0.05) and F = 4.018. Sleep latency in minutes was 14.8 ± 15.2 in the excellent group, and 30.8 ± 28.5 in the average group (p < 0.001) and F = 15.334. Subjective sleep rating was 0.63 ± 0.92 for the excellent students and 1.5 ± 0.95 for the average students (p < 0.001) and F = 29.3. Table 3 showed weekdays and weekends bedtime and wake-up times: the excellent group weekdays and weekend bedtime were 11.54 pm ± 1.54 h and 12.54 am ± 3.36 h respectively, while in the average group they were 1.12 am ± 1.42 h and, 2.48 am ± 2.12 h respectively, with significant statistical difference between the two groups (P < 0.001) and F = 15.628 and 14.271 respectively. No significant statistical difference was evident between the two groups as regards weekdays wake- up time (P = 0.209) and F = 1.592. Regarding weekend wake-up time, it was 8.24 am ± 2.54 h in the excellent group and 10.48 am ± 3.33 h in the average group, with a significant statistical difference between the two groups (P < 0.001) and F = 19.711.

The bedtime delay during weekends was 1.2 ± 1.8 h in the excellent group and 1.6 ± 1.7 in the average group, with no significant difference between the groups (P = 0.232) and F = 1.441. Regarding wake-up delay during weekend it was 2.1 ± 2.0 in the excellent group, and 3.8 ± 2.2 in the average group, with statistical difference between the two groups, (P < 0.001), and F = 25.031.

Media Contacts:
David L. Chandler – MIT
Image Source:
The image is credited to MIT.

Original Research: Open access
“Sleep quality, duration, and consistency are associated with better academic performance in college students”. Kana Okano, Jakub R. Kaczmarzyk, Neha Dave, John D. E. Gabrieli & Jeffrey C. Grossman.
npj Science of Learning doi:10.1038/s41539-019-0055-z.


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