“You better get a good night’s sleep; you have a big exam tomorrow.” It’s a common phrase we hear, but as it turns out we may need more than one good night’s sleep to do well on exams. We’ve always known that good sleep is critical for good academic performance. However, we still don’t have a good understanding of the relationship between sleep and academic performance. How much sleep should we get? Does it matter when we sleep? Can we make up for lost sleep?

In our recently published study we set out to find answers to some of these questions. We distributed 100 Fitbits to college students in one chemistry class and monitored their sleep and class performance during an entire semester. From this dataset, we found that sleep amount, quality, and consistency all play a part in academic performance. *  We found that more hours of sleep, better quality, and higher consistency all contributed to better grades in the course. For example, the average course grades for students averaging seven and a half hours of sleep were 50% greater than students who got one less hour of sleep on average. Similarly, average grades for students who experienced one and a half hours of variability in daily sleep were 45% greater than students who experienced two hours of variability.

More importantly, we found that sleep is critical the night when the learning happens. For instance, if you have an exam that tests what you learned in the last 4 weeks, the amount, quality, and consistency of sleep you get during those 4 weeks is what matters. This ties in nicely with the theory of sleep’s role in memory consolidation. The content that we learn each day is consolidated in our memory though sleep. If you don’t get sleep, we do not have the opportunity to organize and store the content learned in our memory. What surprised us the most was that approximately a quarter of test score variance was explained by sleep measures. That’s more variance than SAT scores account for (It’s been reported that SAT scores account for about 23% of the variance in college grades). We essentially found that sleep measurements can predict academic performance better than SAT scores.

We found interesting gender differences in sleep as well. In general, females tended to get better quality sleep compared to males. It also seemed the females handled day-to-day sleep variance better than males. For instance, when males got variable amounts of sleep from day-to-day, it significantly impacted their sleep quality. This was not the case for females. They tended to be more tolerant to day-to-day changes in sleep schedule and their sleep quality was not affected as much by it. Numerous studies have reported that females generally outperform males in school throughout grade school and college (this contrasts with males outperforming females in standardized tests). Our study again replicated those results, with females significantly outperforming males in overall score in the class. However, when we took sleep differences into consideration, the score differences disappeared. In other words, if males and females got the same amount, quality, and consistency in sleep, their grades would not differ significantly.

Although this study was carried out on college students looking at their academic performance, I think there’s a lot you can take away no matter your age or what your daily life requires you to do. For instance, we found that regardless of the amount of sleep you get, once you pass a certain bedtime, your sleep quality declines. Our bodies have a circadian rhythm and we should follow it in order to get the best quality sleep we can get. It also benefits us to have a consistent sleep schedule. Try to get a consistent amount of sleep every day. The sleep you lost is gone for good, so the best thing to do is focus on resetting and starting a new consistent sleep routine.

*Quality was based on Fitbit’s proprietary algorithm that takes into consideration factors such as sleep duration, movement, and heart-rate variability to calculate the quality of sleep. Consistency was calculated by looking at the variance in sleep amount from day to day. In other words, high consistency meant that people were getting roughly the same amount of sleep each night. Low consistency meant that people were getting 4 hours of sleep one day and 10 hours another day.