Exercise, Depression, and Anxiety in Young People: A Cross-Sectional Survey

1  Introduction

To cope with the COVID-19 pandemic, 143 countries imposed nationwide mandatory school closures at all levels starting in March 2020, affecting a total of 43,518,726 learners around the world [1,2]. While these lockdown policies protected the vulnerable population, they also brought negative mental impacts on young people, particularly anxiety and depression [3]. A recent meta-analysis illustrated that the prevalence of anxiety and depression for university students during COVID-19 was 31% and 34%, respectively, which were considerably higher than before the pandemic [4]. Among young adults in the United States (US), the prevalence of depression and anxiety during COVID-19 was 43.3% and 45.4%, respectively [5]. Depression and anxiety could have adverse effects on university students from an individual, family, and social perspective. A cross-sectional study reported that depression predicts less happiness [5], while recent systematic reviews have shown that anxiety and depression are associated with addiction to the Internet and mobile phones among university students [6,7]. Moreover, two studies have proposed that higher levels of anxiety and depression are associated with a diminished quality of life [2,8], while studies from the US and India have reported that university students with high depression and anxiety have a poorer quality of sleep [9,10]. In terms of eating behaviour, previous research has shown that university students are more likely to suffer from eating disorders due to increased depression and anxiety [11,12]. In addition to these lifestyle behaviours, depression and anxiety also predict higher use of alcohol, marijuana, and nicotine [13,14] and greater susceptibility to risky sexual behaviour among university students [15,16]. Furthermore, several studies have even reported a correlation between depression, anxiety, and higher rates of self-harm and parasuicide [17–19]. In terms of academic performance, anxiety, and depression can predict lower grade point averages and a tendency to drop courses among university students [20–22]. Meanwhile, in a study on student-athletes, preseason anxiety was found to predict sports injuries in the prospective season [23]. Anxiety and depression are also interrelated with body image and obesity in general university students [24,25], while previous studies have shown that anxiety and depression are correlated with obesity [26–28].

Multitudinous observational studies have proposed that higher levels of PA or exercise are interrelated with lower levels of depression and anxiety symptoms among university students [29–33]. Moreover, a current meta-analysis demonstrated the effectiveness of exercise intervention, including aerobic exercise, traditional Chinese exercise, mind–body exercise, muscle-strengthening training, and high-intensity interval training, in reducing depression and anxiety symptoms among university students [34–41].

University students are undergoing a distinct phase in their lives, where they are obtaining considerable knowledge and skills while also beginning the huge transition from school to society. Consequently, they differ from adolescents and adults in their physical, psychological, and social perspectives. Previous research has proposed that the prevalence of depression and anxiety in university students is high, and both mental disorders have negative psychological, physical, academic performance, and lifestyle impacts, and even suicidal tendencies, in university students [4–13]. Exercise, as a changeable lifestyle behaviour, has been demonstrated in previous systematic reviews to be highly acceptable and effective in reducing depression and anxiety in university student populations [34–41]. Nevertheless, there is a lack of sufficient observational studies to explore the correlation between exercise and depression and anxiety in the university student population, which would provide reliable evidence for subsequent interventions and policy development. Moreover, previous research on the correlation between exercise and depression and anxiety in university students was conducted in China, Iceland, and other countries, with a lack of representative study samples from the massive population of American university students [29–33]. To the best of our knowledge, the Healthy Minds Study (HMS), which is the largest national study of university student mental health in the US, did not contribute to studies on the correlation between exercise and depression and anxiety [42]. Furthermore, the majority of the present studies have focused on the period after the outbreak of COVID-19, and there is a lack of research on pre-pandemic data [4]. The availability of pre-pandemic epidemiological data could contribute to carrying out pre-and post-COVID-19 comparisons of prevalence.

Accordingly, to contribute to the above research gaps, we identified two specific aims for this present study: 1) investigating the prevalence of exercise, depression, and anxiety and 2) exploring the association between exercise, depression, and anxiety among American university students in the 2018–2019 academic year.

2  Methods

2.1 Study Design

This study, which was cross-sectionally designed, secondarily analysed available data from the HMS 2018–2019 academic year (https://healthymindsnetwork.org/). As an annual, countrywide, cross-sectional survey conducted on the Internet, the HMS investigates physical, mental, and social health domains among university students in the United States [42]. Demographics, mental health status, and mental health survey utilization/help-seeking are three mandatory modules for colleges and universities who voluntarily participate in this survey, while additional optional modules are selected by their institutions. In the 2018–2019 HMS survey, researchers from the University of Michigan and Boston University recruited students aged 18 and higher from 79 small universities without any exclusion criteria via email. A sample of 4000 students was randomly recruited in institutions with >= 4000 learners, and all students were recruited in institutions with <4000 learners. The overall response rate was 16%. This survey was managed by Qualtrics, and the signed online consent form was obtained from all the subjects before participation. Ethical approvals for the HMS were provided by the ethics committees of all involved universities. The present study was exempt from the approval of the ethics committee due to its secondary analysis of anonymous data from HMS, a publicly accessible database.

2.2 Measures

2.2.1 Exercise

A single-selection question, whose validity and acceptability in previous waves of the HMS survey has been demonstrated [42], was performed as a self-reported measurement to assess exercise among participants. The question was: “In the past 30 days, how many hours per week on average did you spend exercising?”, while the answers were composed of: “Less than 1 h”, “2–3 h”, “3–4 h”, and “5 or more hours”.

2.2.2 Depression

The Patient Health Questionnaire-9 (PHQ-9), which is a self-administrated tool composed of the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV)’s nine criteria for a depressive disorder, was applied to measure depression among participants [43,44]. In the US adult population, the reliability and validity of the PHQ-9 are 0.89 and 0.88, respectively [45]. The PHQ-9 investigates how often participants are troubled over the last two weeks using the nine criteria, such as “Little interest or pleasure in doing things.” Each criterion is rated from “0” (not at all) to “3” (nearly every day). Participants are screened for depression based on their overall scores as either negative (scores 0–9) or positive (scores 10–27) [43,44], thus converting the overall score into a dichotomous variable.

2.2.3 Anxiety

The Generalized Anxiety Disorder 7-Item (GAD-7) scale, which is a self-reported instrument consisting of DSM-IV’s seven criteria for generalized anxiety disorder, was applied to measure anxiety among the participants [45]. The reliability and validity of the GAD-7 in the US adult population are 0.92 and 0.83, respectively [45]. The GAD-7 explores how often participants are troubled over the last two weeks using seven criteria, such as “Trouble relaxing, becoming easily annoyed or irritable, etc.” Each criterion is rated from “0” (not at all) to “3” (nearly every day). Participants are screened for anxiety based on their overall score as either negative (scores 0–9) or positive (scores 10–22) [45], thus converting the overall score into a dichotomous variable.

2.2.4 Covariates

Sociodemographic characteristics, which consisted of age, sexual orientation (male, female, trans male, trans female, genderqueer, and self-identified), international students (Yes or No), race (Black, American Indian or Alaskan Native, Asian, Latino, Native Islander, Middle Eastern, Arab, White, other race), and residence were identified as covariates for further analysis.

2.3 Statistical Analysis

All statistical analyses were performed using SPSS 26.0. The study respondents’ characteristics, independent variables, and outcomes were reported using a descriptive approach. The multivariable logistic regression model was employed to explore the association between exercise and depression and anxiety, controlling for age, gender, race/ethnicity, and international students. All results were presented as an odds ratio (OR) with 95% confidence intervals. All statistical analyses considered a weighted sample. Statistical significance was set as p < 0.05.

3  Results

3.1 Demographic Characteristics

The demographic characteristics of the participants are presented in Table 1. A total of 62,026 participants, of which 65.9% were female, were included in the final analysis during the 2018–2019 academic year. The majority of participants were in the 18-to-24-year-old age group (77.1%) and non-international students (91.8%), while residence status and race were diversely distributed.

3.2 Prevalence of Exercise and Mental Disorders

From Table 2, it can be seen that 24.6% of the participants exercised at least 5 h daily, while the prevalence of depression and anxiety was 25.7% and 22.3%, respectively.

3.3 Association between Exercise and Mental Disorders

We observed that those participants who exercised less were prone to experience depression and anxiety compared with participants who exercised at least 5 h daily. Table 3 shows that exercise times of less than 1 h daily (OR = 1.31 [1.29, 1.33]), 2 to 3 h daily (OR = 1.13 [1.11, 1.15]), and 3 to 4 h daily (OR = 1.04 [1.02, 1.06]) were correlated with greater odds of depression. As for anxiety, it was associated with exercising for less than 1 h daily (OR = 1.23 [1.21, 1.25]) and for less than 2 to 3 h daily.

4  Discussion

To the best of our knowledge, HMS is the largest study on university students in the area of mental health. The present study first explored the correlation between exercise and depression and anxiety in this database. The Results showed that the prevalence of PA is low, while the prevalence of the two mental disorders is high. Prolonged exercise was a protective factor against depression and anxiety, and lower exercise levels were significantly correlated with depression and anxiety. Our study contributes to the growing body of literature investigating the correlation between exercise and mental disorders in university students and provides a reference to compare the prevalence and correlation across countries and time.

As a modifiable lifestyle behaviour, many organizations and countries have promoted PA through the development of PA guidelines due to its benefits to individuals and all of society [28,46]. The 2018 PA Guidelines for Americans recommends that, every week, university students should perform 150 to 300 min of moderate-intensity aerobic exercise, 75 to 150 min of high-intensity aerobic exercise per week, or an equivalent combination of moderate-and high-intensity aerobic exercise [46]. In this study, nearly half of the participants met the recommended PA level, which is higher than the findings in US adolescent population research before the outbreak of COVID-19 [47,48]. One possible explanation for the exercise conflict is that the measurement applied in this study is different from the ones used in other observational studies. In large-scale observational studies, self-reported questionnaires, particularly the international PA questionnaire, are often applied to assess the level of PA, taking into account reliability, validity, and cost-effectiveness [49,50]. IPSQ-SF can explore time costs in different PA intensities and, thus, compare the results with the majority of PA guidelines. On the contrary, the measurement used in this study did not distinguish specific time costs at different PA intensities. Therefore, some participants who exercise 2–3 h a week may not meet the equivalent combination of moderate-and high-intensity aerobic exercise, leading to an overestimation of the prevalence of students meeting PA levels. Moreover, participants may overestimate their PA due to the 30-day-long recall period, as well as the influence of social desirability and social approval [51,52].

The prevalence of depression in this study resembles the results of the 2005–2018 HMS academic year, as well as pre-COVID-19 studies among university students in other regions [53–55]. Whilst the PHQ-9 cannot be used as an instrument for the clinical diagnosis of depression, it helps to detect the prevalence of depression at the population level. As part of a national cohort study using the same measurement, the prevalence of depression in the 2005–2018 HMS academic year was similar to the results of this study, which may be due to controlling for inclusion criteria and confounding factors. External factors such as the participants’ geographical location, sociocultural background, and other factors can significantly influence the prevalence of mental disorders at a population level.

In this study, the prevalence of anxiety resembles the results of the 2015–2017 HMS academic year [56], whereas there were increases of 7.0% to 27.0% compared with the prevalence in the 2007 and 2009 HMS academic years [53]. Even considering the growing trend in the prevalence of anxiety disorders in university students [11,57], it is also possible that such considerable growth, even after controlling for inclusion criteria and confounding factors, may be the result of differences in measurement instruments. The anxiety measurements for the 2007 and 2009 HMS academic years were concise screens using the PHQ, whereas this study used GAD-7. However, in the 2015–2017 HMS academic year, which also used the GAD-7, the prevalence of anxiety was similar to that of this study, indicating that different measurement instruments can reduce the comparability of mental disorders.

To the best of our knowledge, this study, which investigated data from the 2018–2019 HMS academic year, is the first to explore the correlation between exercise and depression and anxiety in the HMS. Our study reported that university students who exercise less than five hours a week had a significantly greater risk of depression compared with those who exercise more than five hours per week. As for anxiety, those who exercise less than three hours per week have a significantly higher risk of anxiety compared with those who exercise more than five hours per week. Our findings are consistent with extant meta-analyses that have found that higher levels of exercise correlate with lower levels of depression and anxiety in university students [58,59]. Moreover, the association between more exercise and lower levels of anxiety and depression has also been reported in studies conducted after the COVID-19 outbreak [60]. As a specific group, university students are transitioning from adolescence to adulthood; thus, different mechanism hypotheses may exist to explain the effectiveness of PA intervention on the mental health of university students, such as neurobiological, psychosocial, or behavioural factors [61]. The neurobiological mechanism hypothesis suggests that PA promotes mental health by altering the function and structure of the brain, particularly neuroimaging changes in frontal lobe area activation and electrophysiological parameters [62]. A study by Gondoh showed that exercise training maintains grey matter volume in the left insula of university students and enhances their mental health [63]. Moreover, monoamine and neurotrophin hypotheses have also been proposed [64]. The possible psychosocial mechanisms include positive variations in physical self-concept and the positive effects of acute exercise on transient mood [65,66]. According to the behavioural mechanism hypothesis, PA can contribute to mental health through effective self-regulation and physical self-regulation [61].

4.1 Limitations and Further Recommendations

Several limitations inevitably exist in this study. First, exclusion criteria for participants were not identified (e.g., participants with a physical disability or clinically diagnosed mental disorders), which may introduce bias. Second, the cross-sectional study design was incapable of verifying causal inferences. Third, the exercise measures in this study did not differentiate between different PA intensities, and the correlation between different PA intensities and mental disorders varied. Therefore, the unsegmented exercise measurement may cause bias in this study. Fourth, exercise was subjectively measured based on a long-term recall period of 30 days, which may cause bias due to a social desirability effect and memory error. Finally, depression and anxiety were measured by using standardised questionnaires, which are valid and reliable but are not a substitute for clinical diagnosis. Accordingly, future studies need to identify exclusion criteria for participants, apply longitudinal and retrospective designs, and objectively measure the appropriate variables to provide more precise evidence.

5  Conclusion

The present study suggests that the prevalence of exercising for more than 5 h daily is low among American university students, and the prevalence of depression and anxiety is high. Moreover, within this population, higher levels of exercise may be positively associated with lower levels of depression and anxiety. Community and school interventions should prevent or reduce anxiety and depression by increasing exercise participation among university students, thereby promoting both physical and mental health.

Acknowledgement: Thank all those who have helped us in this research.

Funding Statement: The authors received no specific funding for this study.

Author Contributions: The authors confirm contribution to the paper as follows: study conception and design: Meiling Huo, Zhen Yang; data collection: Meiling Huo; analysis and interpretation of results: Meiling Huo; draft manuscript preparation: Meiling Huo, Zhen Yang. All authors reviewed the results and approved the final version of the manuscript.

Conflicts of Interest: The authors declare that they have no conflicts of interest to report regarding the present study.