The Impact of Sleep Deprivation on Sickness Incidence Among College Freshmen: A Review

Introduction

Incoming freshmen entering college seem to get sick at higher rates than upperclassmen. This phenomenon is colloquially referred to as the “freshman flu,” a general term for contracting general illnesses or exhibiting symptoms such as a cough or runny nose. This phenomenon could be partly due to a lack of sleep. 

College students are at risk for sleep deprivation, with up to 70% of college students experiencing poor sleep quality, and among them, freshmen have the highest incidence of poor sleep quality compared to upperclassmen. The average recommended sleep duration for 18-year-olds, the typical age of college freshmen, is 8 to 10 hours. However, on average, most college students receive approximately 416.5 ± SD 68.6 minutes of sleep (less than 7 hours) on a typical night. Sleep can be exacerbated by factors such as overnight studying before exams or late-night social activities. 

Surveys done by Li et al. have shown that freshmen have poorer sleep quality and higher rates of excessive sleepiness, which increases the risk of mental disorders and worsens physical health.  A stratified cluster sample of 6,284 college students surveyed using the Pittsburgh Sleep Quality Index (PSQI) revealed that freshmen have poorer sleep quality and higher rates of excessive sleepiness compared to upperclassmen, which worsen both physical and mental health. In addition to the higher incidence of poor sleep quality, freshmen were also found to have less high quality sleep than any other grade as well, with seniors having more than 5% “good sleep” than freshman, which was statistically significant (P=.002).

A study of 5,692 participants by Kolla found that 18-year-olds had the highest prevalence of excessive sleepiness, followed by college students, who experienced greater rates than employed individuals.  Excessive sleepiness was also linked to an increased risk of mental health issues, including anxiety, behavior, mood, and substance use.” 

Sleep deprivation among college freshmen can be detrimental to immune, cardiovascular, and neurological health. This review aims to explore the negative health effects of sleep deprivation and clarify the ‘freshman flu’ phenomenon.

Results

The search yielded studies examining the impact of sleep deprivation on immune, neurological, and cardiovascular health through cross-sectional surveys, longitudinal studies, and experimental research. Notably, these findings are especially relevant to college freshmen, who experience some of the worst sleep quality among all college demographics. Given their transition into a new environment, shared living spaces, and elevated academic and social pressures, freshmen are particularly vulnerable to both sleep deprivation and increased exposure to pathogens. The physiological effects of sleep deprivation—such as reduced natural killer cell activity, increased inflammation, impaired neurological processing, and cardiovascular strain—may explain why freshmen are more prone to general sickness. These mechanisms provide biological plausibility for the “freshman flu” phenomenon, in which poor sleep contributes directly to reduced immunity and higher incidence of illness in this specific population.

Sleep Deprivation and the Immune System

Sleep deprivation impairs immune function by reducing natural killer (NK) cell activity and increasing inflammatory proteins, such as IL-6, which can lead to an improper immune response and a higher incidence of sickness. In addition, sleep deprivation also leads to a decrease in CD4 T Cells, neutrophil phagocytic activity, and reduced stimulated production of interleukin 2 and 12 (IL-2 and IL-12), all of which contribute to a higher incidence of sickness and a diminished immune response.

Sleep deprivation also impairs immune function and host defense. This impairment is partly due to the role of non-specific lymphocytes such as natural killer cells and prostaglandins (PGs). NK cells are responsible for destroying potentially harmful cells in early stages, while PGs primarily regulate certain parts of the immune system. Specifically, prostaglandin E is involved in generation of T suppressor cells, which helps maintain homeostasis and regulate immune responses. Studies show that participants in the sleep-deprived group (88 hours) experienced increased generalized body pain, physical discomfort, headache, stomach and muscle pain compared to those with a regular sleep schedule, suggesting that PGE2 may mediate the pain-enhancing effects of sleep loss. Overall, the downregulation of both NK cells and PGs due to sleep deprivation significantly impairs immune function and the body’s ability to fight off sickness.

Sleep Deprivation and Neurological Health

Sleep deprivation disrupts critical brain functions, particularly those related to stress regulation, cognition, and emotional stability. It decreases slow-wave activity (SWA), which is essential for memory consolidation and physical recovery, and it increases circulating cortisol levels, contributing to anxiety and mood instability. These changes impair the brain’s ability to manage both mental and physical stress, which can reduce academic performance and further weaken the immune system.

For college freshmen, who are already adapting to new social, academic, and environmental pressures, these neurological disruptions can be especially damaging. The inability to concentrate, retain information, or regulate emotions makes students more vulnerable not only to stress-related disorders but also to physical illness due to the close connection between brain function and immune regulation.
Animal studies further demonstrate the dangers of prolonged sleep loss. In a landmark rat study, Rechtschaffen and Bergmann (2002) found that total sleep deprivation over two to three weeks resulted in severe physiological deterioration, including increased circulating stress hormones, ulcerative skin lesions, and eventual death. These effects were linked to the loss of restorative NREM sleep, highlighting the critical role of deep sleep in maintaining systemic health.

Sleep Deprivation and Cardiovascular Health

Sleep deprivation also impacts cardiovascular health. A study done by Yang and colleagues (2018) investigated the relationship between sleep deprivation and excess heart age (EHA), defined as the difference between heart age and chronological age. The study found that the mean EHA, adjusted for cardiovascular risk factors such as smoking or high cholesterol, was lowest in adults who reported sleeping 7 hours per night, and increased as adults reported sleeping fewer hours. In simple terms, the less sleep an individual gets, the older their heart appears.

A further effect of sleep deprivation involves the autonomic regulation of cardiac function. It was found that sleep-deprived individuals have significantly lower exercise capabilities and higher systolic BP.14 Both of these factors indicate the effect sleep deprivation has on heart health, and more specifically, the recovery of heart rate, which was demonstrated in a study by Cincin et al. (2014). The researchers found that, compared to individuals who had a normal night of sleep, sleep-deprived participants showed significantly lower exercise capacity, higher peak systolic blood pressure, and impaired heart rate recovery. Specifically, exercise capacity declined from 11.71 ± 1.30 METs after regular sleep to 10.96 ± 1.01 METs following sleep deprivation (p = 0.002), indicating reduced physical performance. METs, or Metabolic Equivalents of Task, are a standard unit used to estimate the amount of energy the body uses during physical activity. 1 MET is defined as the energy you use when you’re at rest (sitting quietly), which is approximately 3.5 mL of oxygen per kilogram of body weight per minute.

Additionally, peak systolic blood pressure increased from 166.2 ± 9.9 mmHg to 173.8 ± 16.3 mmHg (p = 0.019), showing increased cardiovascular strain.14 Most notably, heart rate recovery at 30 seconds (HRR30) dropped from 17.66 ± 5.46 bpm to 12.74 ± 6.19 bpm (p = 0.003), and at one minute (HRR1), it decreased from 36.10 ± 7.78 bpm to 31 ± 6.49 bpm (p = 0.004). These findings emphasize the negative impact of sleep deprivation on the cardiovascular system, especially in terms of exercise response and recovery, even in healthy young adults.

Sleep deprivation is associated with arterial stiffness in young adults, a marker of cardiovascular aging that increases the risk of heart disease and mortality. In a study by Sunbul et al. (2014), 30 healthy young adults were subjected to one night of total sleep deprivation and compared to a control group with normal sleep. The results showed that the sleep-deprived group had a significantly higher pulse wave velocity (PWV)—a direct indicator of arterial stiffness—measuring 6.9 ± 1.1 m/s compared to 6.2 ± 0.9 m/s in the control group (p < 0.01). Additionally, augmentation index (AIx), another marker of vascular stiffness, was elevated in the sleep-deprived group (17.1 ± 6.8% vs. 13.2 ± 6.1%, p < 0.05). These findings demonstrate that even short-term sleep deprivation can cause measurable vascular changes that reflect early cardiovascular aging.

Discussion

Summary of Evidence: The reviewed studies indicate that sleep deprivation has numerous adverse effects on health, negatively impacting immune, neurological, and cardiovascular functions. As freshmen have been shown to be generally more sleep deprived, these factors may collectively contribute to a higher incidence of sickness, known as the “freshman flu.”

It is critical for students to have a robust immune response in densely populated environments such as dormitories, shared bathrooms, and college classrooms, in which students are frequently exposed to new pathogens due to the diverse student populations. Inadequate sleep leads to an increased inflammatory state and poorer responses to pathogens. College students, especially freshmen, need to be in peak neurological and physical health to handle the demands of academics, social adjustments, and exposure to new environments. Unfortunately, sleep deprivation disrupts the body’s entire regulatory system. It weakens the immune system, making it harder to fight off pathogens. Sleep deprivation also disrupts neurological processes such as slow-wave activity and stress regulation, increasing levels of cortisol and reducing resilience to both physical and mental stressors.

This chain reaction contributes directly to the phenomenon commonly referred to as the “freshman flu.” A weakened immune response means that students are more susceptible to viruses circulating in close-contact environments like dorms and lecture halls. At the same time, impaired neurological regulation makes it harder to manage stress and concentrate, further reducing the body’s ability to recover. Cardiovascular strain adds to the burden, with increased heart rate, arterial stiffness, and fatigue—all of which amplify the toll on a student’s health.

In this way, the body acts as a connected system: when sleep deprivation knocks one part out of balance, the effects ripple outward. A tired brain can’t properly manage the immune system; a stressed cardiovascular system can’t support recovery. The result is a feedback loop of stress, sickness, and poor academic performance—a cycle that defines the freshman experience for many.

Addressing sleep deprivation in college freshmen is crucial for improving their overall health and reducing the incidence of sickness. Colleges/universities should promote good sleep habits and highlight the risks of sleep deprivation, as interventions to improve sleep hygiene and increase sleep duration could enhance the overall health of the student bodies. Colleges and universities should promote good sleep habits and highlight the risks of sleep deprivation, as interventions to improve sleep hygiene and increase sleep duration could enhance the overall health of the student body. Many students struggle with irregular sleep schedules, excessive screen time, and academic stress, all of which contribute to poor sleep quality. By encouraging consistent sleep routines, limiting caffeine intake, and promoting relaxing pre-sleep activities, institutions can help students develop healthier habits. Additionally, educating students about the negative effects of sleep deprivation—such as impaired memory, reduced academic performance, and increased risk of mental and physical health issues—can motivate behavior change. Implementing wellness programs, offering workshops on sleep hygiene, and creating environments that support rest can lead to better sleep and, in turn, improved academic success and overall well-being.

Limitations: The review is limited by the variation in study designs, sample sizes, and measurement techniques used across the included studies. Additionally, most studies rely onself-reported sleep data, which may introduce bias.

Conclusion

The overarching cause for the “freshman flu” can be partially attributed to sleep deprivation. Poor sleep may lead to various health issues, including a diminished immune response and functioning of NKs or CD4 T cells. These factors, coupled with a decrease in neurological, cardiovascular health, and exposure to diverse pathogens from tight-knit environments, can lead to a heightened prevalence of general sickness among freshmen. University leaders can promote sleep health and raise awareness about the dangers of sleep deprivation, which has become increasingly prevalent. Such efforts could improve the health of freshmen and contribute to healthier campuses overall.