Most students focus on studying harder when their grades slip, but research shows that what you eat, how you sleep, and whether you exercise may matter just as much as the hours you put into your books. A peer-reviewed study published in PeerJ examined over 600 university students and found clear links between everyday health behaviors and self-reported GPA.
What the Study Found
While the terms “academic performance” and “academic success” are widely used, there is no easy or universally acknowledged definition of either term. In the United States and many other countries, grades and GPA are used as the primary measures of academic success. Researchers at a public university in southwest Florida surveyed 614 undergraduate students over two years, asking about 28 health behaviors across five categories: sleep, work, physical activity, diet, and substance use. Students self-reported their current GPA, and statistical models were used to find which habits made a measurable difference. The average GPA across all participants was 3.39 out of 4.0.
Although adherence to appropriate health behaviors can facilitate a healthy lifestyle in adulthood, the transition to college is often accompanied by an increase in unhealthy behaviors. According to the Office of Disease Prevention and Health Promotion, students who follow public health recommendations achieve higher GPAs. Health-promoting behaviors such as regular sleep, adequate physical activity, and frequent breakfast intake are positive predictors of GPA. On the contrary, unhealthy behaviors such as smoking, drug use, fast food consumption, and working long hours have been identified as negative predictors of academic performance.
Sleep and GPA
Getting the right amount of sleep is one of the most important things a student can do for their grades. Sleep is not only a biological necessity but a vital component for memory consolidation, decision making, and learning. Sleep quality and quantity are among the most researched health behaviors in connection with academic performance, and there is a strong consensus that both affect students’ grades.
The study found that students who slept 4 hours or less per night had significantly lower GPAs than those who slept 6, 7, or 8 hours. Interestingly, sleeping too much also hurt performance — students who averaged 9 or more hours per night had lower GPAs than those who slept 8 hours. Freshmen at risk for a sleeping disorder or infrequent restful sleep received lower grades, and four out of ten college freshmen reported chronic sleep deprivation in a related study.
The timing of sleep — whether students went to bed early or late — did not matter as much as the total number of hours slept. Some earlier studies claimed that sleep timing is a better predictor of academic performance than actual hours slept, but this study found that a student who went to bed at 2 AM and still got 8 hours of sleep performed just as well. Both sleep amount and quality play a role, and students should prioritize consistent, sufficient rest above all.
Key takeaway for sleep:
7 to 8 hours per night is the sweet spot for academic performance
Both under-sleeping and over-sleeping are associated with lower GPAs
Bedtime does not matter as long as total sleep is sufficient
Work Hours and GPA
Because of the rising costs of attending university, there has been a sharp increase in the number of students relying on income from working while in college. Seven out of ten students work during the semester, and nearly half average over 20 hours per week. There is a strong consensus among published studies that the number of hours full-time students work negatively affects their academic performance.
Students who worked 20 or more hours per week reported noticeably lower GPAs. Students who did not work at all or worked up to 10 hours per week reported average GPAs above 3.45, whereas those working 10 or more hours had GPAs of 3.38 or less. A separate study confirmed lower GPAs for students working more than 11 hours per week, and students working over 31 hours had the lowest GPAs of all.
Work hours vs. GPA at a glance:
Physical Activity and GPA
One in six students in the study reported being completely physically inactive. Basic cognitive functions related to attention and memory are enhanced by physical activity, according to the Institute of Medicine. More frequent use of a university’s recreation center was also associated with higher GPAs in a related study.
Both aerobic exercise and strength training were positively associated with higher GPAs. Students who did strength training on four or more days per week reported a GPA of 3.51, compared to 3.28 for students who did no strength training at all. Higher levels of physical activity are positively associated with a higher GPA across multiple studies, though the strength of the effect varies by study design.
Eating Habits and GPA
Healthy eating habits have been shown to positively influence academic performance in research from multiple countries. Diet quality appears to be the main factor for this effect — students with lower overall diet quality are significantly more likely to perform poorly on assessments. A healthy diet is effective in improving cognitive functioning and academic performance, though not all studies agree on which specific habits matter most.
A review of seven studies found that five reported higher academic achievement with increased fruit intake, while other studies including Reuter, Forster & Brister (2020) did not find that association. Three eating habits, however, stood out clearly:
Breakfast: Students who ate breakfast every day had significantly higher GPAs than those who skipped it. The positive effect of eating breakfast regularly has been reported across different countries, and breakfast consumption had one of the highest effect sizes of all 28 behaviors tested.
Fast food: As fast food consumption increased, GPA went down. As fast food intake increased, GPA successively decreased, and this was confirmed by Deliens et al. (2013) as well.
Energy drinks: Students who consumed energy drinks had lower GPAs. Energy drink consumption has a significant negative association with GPA, and this was supported by multiple other studies as well as Buchanan & Ickes (2015).
Alcohol, Vaping, and Marijuana
The two most commonly abused substances among college students are alcohol and marijuana, and both have been shown to decrease academic performance in multiple studies. Substance use showed consistent negative associations with GPA:
Alcohol: More frequent alcohol consumption is negatively correlated with GPA, and students who had consumed alcohol at least once in their life reported lower GPAs. A national study confirmed drinking as a negative predictor of academic performance, and Souza, Hamilton & Wright (2019) found similar results in Brazilian university students.
Cigarette smoking: Smoking was a negative predictor of cumulative GPA. According to the American Lung Association, smoking among high school students dropped from 38.4% in 1999 to just 8.8% by 2018, which is reflected in the study’s low smoking rates.
Vaping: One-third of students (35.9%) had used electronic vaping products at least once, and those students reported lower GPAs. Induced oxidative stress from e-cigarettes can be linked to cognitive impairment and attention deficit. Leas et al. (2020) reported that almost one-third of young adults had used at least one tobacco product including e-cigarettes.
Marijuana: 44.2% of students had used marijuana at least once, and these students reported lower GPAs. Marijuana use trajectories show that more frequent users have the lowest GPAs. Wallis et al. (2019) and Souza et al. (2019) both confirmed a negative relationship between marijuana use and academic success.
There is also a long history of students using stimulants to improve academic performance, but research shows that stimulant users had lower average GPAs than nonusers, spent less time studying, and skipped class more frequently. Data from the 2017 National Survey on Drug Use and Health confirms that prescription drug misuse among 18 to 25-year-olds aligns with levels found in this study.
Why These Habits Matter (But Are Not Everything)
An important nuance from the study is that while these associations were statistically significant, the effect sizes were relatively small. Sleep alone explained only 5% of the variation in GPA scores across students. This means health habits are one piece of the puzzle — study time, course difficulty, support systems, and motivation all matter too.
A comparison of health-promoting behaviors across seven UK universities found marked differences between student populations, illustrating how regional and institutional culture shapes behavior. Generation Z students — those born after 1996 — show different health behaviors and habits compared to Millennials, making this study especially relevant for today’s college population.
Practical Tips for Students
Based on the research, here are habits that are most likely to support better academic performance:
Sleep 7 to 8 hours every night, regardless of when you go to bed
Eat breakfast daily — even something small counts
Exercise at least 4 days per week, including some strength training
Keep work hours under 10 per week if possible, and never exceed 20 hours
Reduce fast food and avoid energy drinks
Avoid alcohol, vaping, and marijuana — even occasional use is linked to lower grades
Who Was Studied
The study included 614 undergraduate students aged 18 to 25 at a regional public university in Florida. The group was 78.5% female and 21.5% male. Research has shown that female students are more likely to participate in online health surveys in general, which explains the imbalanced gender ratio in the sample. The survey instrument was modeled on the 2017 Standard High School Youth Risk Behavior Survey published by the CDC.
Frequently Asked Questions
Does sleep really affect college GPA?
Yes. The study found that students sleeping 4 hours or less had significantly lower GPAs than those sleeping 7 or 8 hours per night. Sleep supports memory consolidation and cognitive function, both of which are critical for academic success. Norwegian university students showed the same pattern in a separate large-scale study.
How many hours can a student work without it hurting grades?
Working up to 10 hours per week appears safe and may even slightly benefit GPA. Once work exceeds 20 hours per week, a clear negative impact on grades begins to appear. This is backed by multiple published studies across different universities and countries.
Is skipping breakfast bad for academic performance?
Yes. Breakfast consumption had one of the strongest associations with GPA in this study. Students who ate breakfast every day consistently outperformed those who skipped it regularly. This finding has been replicated in studies from multiple countries.
Does exercise improve academic performance?
Yes. Both aerobic exercise and strength training were positively associated with higher self-reported GPA. Students who exercised on 4 or more days per week had notably higher GPAs than those who were inactive. Higher levels of physical activity are positively associated with a higher GPA across several peer-reviewed studies.
How does vaping affect college students’ grades?
Students who had used vaping products at least once reported lower GPAs than those who had never vaped. The study also found vaping use is still increasing among college freshmen. E-cigarettes may cause oxidative stress linked to cognitive impairment, making it an emerging concern for both health and academic performance.
Does marijuana use affect GPA?
Yes. Students who had ever used marijuana reported lower GPAs than those who had not. More frequent marijuana users have the lowest GPAs, and the association was present even when controlling for frequency of use.
Are these effects large enough to matter?
While statistically significant, the individual effect sizes are modest. Sleep explained about 5% of GPA variation. These habits work best when combined — students who sleep well, eat breakfast, exercise, and avoid substances are likely to see a cumulative benefit on their grades. The original study was published in PeerJ in 2021 and is freely available for reference.
