To the best of our knowledge, this is the first study to explore the relationship between sedentary behavior and depressive symptoms in Japanese medical students during the COVID-19 pandemic. The cumulative number of COVID-19 cases in Japan was 1 708.742 as of October 11, 2021,19 with cases still increasing more than a year after the first infection. Our findings in such a situation emphasized that the COVID-19 pandemic heightened the depressive symptoms of Japanese medical students. That is, they were less physically active and more depressed than non-medical students. Additionally, we found that medical students with depression had more sedentary lifestyles than those without depression.
According to the analysis of Model 1, medical students were less physically active than non-medical students. Medical students are under a great deal of daily mental stress due to pressure to maintain excellent academic performance.20 Moreover, medical students have little time for regular physical activity due to their demanding studies.21 Thus, this was a reasonable finding. Overlapping with this, the forced confinement due to the COVID-19 pandemic may have led them to living a more sedentary lifestyle. Similar to previous studies that showed that the COVID-19 pandemic was linked to sedentary behavior and psychological distress in university students,3,22 our results suggested that medical students with longer sedentary time had worse depressive symptoms.
The analysis of Model 2, which focused on medical students, revealed that depressive symptoms were more prevalent among females than males. In general, it is known that a gender difference exists in the prevalence of depression.23 The fact that gender was not detected as a determinant of depression in our multiple logistic analysis supports previous studies on medical staff during the COVID-19 outbreak.24 Thus, gender may not have been a deciding factor in the development of depression among Japanese medical students during the COVID-19 pandemic. Additionally, longer sedentary behavior and screen time for leisure impacted depressive symptoms in medical students. In contrast, no statistical difference was found for physical activity, which included total physical activity, vigorous activity, moderate physical activity, and walking, between medical students with and without depression.
The causal association between confinement due to the COVID-19 pandemic and depressive symptoms could not be examined in this study. However, the results indicated that sedentary behavior exacerbated depressive symptoms as a result of decreased physical activity due to restrictions on going out. In medical students with depression, the sedentary behavior and screen times were 480.0 and 270.0 minutes per day, respectively. These figures were comparatively higher than those of a recent systematic review that involved 125 studies on university students globally (437.4 minutes per day of sedentary time, 135.6 minutes per day of screen time on smart phones, and 122.4 minutes per day of screen time on computers and video games).25 In a 2014 meta-analysis of the general population, the relative risk of depression was found to be 1.31 (95% CI 1.16-1.48) for sedentary behavior. Additionally, long-term TV viewing and computer or Internet use were cited as factors that increased this risk.26 A previous meta-analysis also suggested that Internet addiction was significantly associated with depression (OR = 2.77).27 This suggests that Japanese medical students should reconsider their behavior at home during confinement to mitigate depression. Moreover, a recent study indicated that prolonged sedentary time was more important than total sedentary time.28 Therefore, there may be a need to manage recreational screen time among medical students.
In Japan, online classes were launched at universities with the issuance of the first emergency declaration in 2020. Since then, online learning has become more common among university students. In ordinary situations, increasing opportunities for outdoor social interaction may help reduce depressive symptoms. However, during an emergency such as the current pandemic, improving mental problems through online interventions at home should be a priority. In recent years, web-based cognitive behavioral therapy has been highlighted as a way to improve psychiatric symptoms among university students.29 Notably, university students use the Internet daily.30 Therefore, future studies on web-based cognitive behavioral therapy interventions and their impact on depression are expected to provide medical students with health promotion and prevention strategies that they can easily use at home.
This study has some limitations. First, the presence or absence of depression was not determined based on a clinical examination. However, the PHQ-2 has been proven to be valid tool for depression screening.17 Second, as all the items were self-reported, recall bias and the respondent’s social setting may have affected the results. Third, as this study had a cross-sectional research design, we were unable to conduct a longitudinal study on the occurrence of depression and sedentary lifestyles. Additional research is necessary to investigate the long-term effects of the sedentary lifestyles of Japanese medical students on depressive symptoms in a large population.