Effects of replacing sedentary time with alterations in physical activity or sleep on mood states in Chinese young adults during the pandemic.

Background: Poor mood states pose the most frequent mental health, creating a considerable burden to global public health. Sedentary behavior is an essential factor affecting mood states, however, previous measures to reduce sedentary time in Chinese young adults have focused only on increasing physical activity (PA). Sedentary, PA, and sleep make up a person's day from the standpoint of time use. It is not known whether reallocating sedentary time to different types of PA (e.g. daily PA and structured PA) or sleep during an epidemic has an effect on mood states. Therefore, this study aimed to examine the association between replacing sedentary time with different types of PA or sleep during the pandemic and the mood states of Chinese young adults and to further examine whether this association varies across sleep populations and units of replacement time.

Method: 3,579 young adults aged 18 to 25 years living in China and self-isolating at home during the COVID-19 outbreak were invited to complete an online questionnaire between February from 23 to 29, 2020. Subjects' PA, sedentary time, and mood states were assessed using the International Physical Activity Questionnaire and the Chinese version of the Profile of Mood States, respectively. Participants also reported sleep duration and some sociodemographic characteristics. Participants were divided into short sleepers (< 7 h/d), normal sleepers (7-9 h/d), and long sleepers (> 9 h/d) based upon their reported sleep duration. Relevant data were analyzed using Pearson correlation analysis and isotemporal substitution model (ISM).

Results: Sedentary time was negatively associated with mood states in Chinese young adults during the pandemic (r = 0.140) and correlated strongest among short sleepers (r = 0.203). Substitution of sedentary time with structured PA was associated with good mood states (β=-0.28, 95% CI: -0.49, -0.08). Additionally, substituting sedentary time with daily PA (e.g. occupational PA, household PA) was also associated with good mood states among normal sleepers (β=-0.24, 95% CI: -0.46, -0.02). The substitution of sedentary time with sleep could bring mood benefits (β=-0.35, 95% CI: -0.47, -0.23). This benefit was particularly prominent among short sleepers. Furthermore, for long sleepers, replacing sedentary time with sleep time also resulted in significant mood benefits (β=-0.41, 95% CI: -0.69, -0.12). The longer the duration of replacing sedentary behavior with different types of PA or sleep, the greater the mood benefits.

Conclusions: A reallocation of as little as 10 min/day of sedentary time to different types of PA or sleep is beneficial for the mood states of young adults. The longer the reallocation, the greater the benefit. Our results demonstrate a feasible and practical behavior alternative for improving mood states of Chinese young adults.