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Objective The Corona Virus Disease-19 (COVID-19) pandemic has evolved into the largest public health event in the world. Earlier COVID-19 studies have reported that the pandemic caused widespread impacts on mental health and sleep in the general population. However, it remains largely unknown how the prevalence of mental health problems and sleep disturbance developed and interacted in adolescents at different times in the epidemic. Methods 831 teenagers (aged 14–19) underwent a longitudinal follow-up study to evaluate the prevalence of mental health problems and sleep disturbance among adolescents before, during, and after the COVID-19 breakout in China and to explore the interaction between mental health and sleep across the three measurements. The chronotype, anxiety and depression level, sleep quality, and insomnia were investigated during each measurement. Results The adolescents had delayed sleep onset and sleep offset time, longer sleep duration during the quarantine than before and after the epidemic, whereas their chronotype tended to morning type during the epidemic. Yet, the highest prevalence of anxiety, depression, poor sleeper, and insomnia symptoms were observed before but not during the COVID-19 breakout. The females and adolescents who were eveningness type showed significantly higher anxiety and depression levels, poorer sleep quality, and severe insomnia status than the males and the intermediate and morning types. Sleep disturbance was positively associated with mental problems among three measurements. Pre-measured depression level significantly predicted sleep disturbance level at follow-ups. Conclusion These findings suggested that adolescents' high prevalence of mental health and sleep problems occurred before the COVID breakout and decreased during and after the epidemic. Gender and chronotype were significant risk factors associated with affective and sleep disturbances. Depression positively predicted later sleep problems, but not vice versa.

This study examines whether the benefits of a short midday nap on habitual nappers' mental performance depend on the cognitive domain and the task difficulty. Eighteen healthy college students with the long-term habit of a midday nap (13:00-14:00 hours) participated in a nap-deprivation study. On two separate days with at least 3 days in between, participants either took a nap or remained awake, and were subsequently tested on a simple sustained attention task (Psychomotor Vigilance Test), two more complex attention tasks (Go/No-Go and Flanker task) and one working memory task (2-back). For each task, an easy and a difficult version were administered. The time course of subjective sleepiness and mood were also measured in both napping conditions. The results revealed that short midday nap deprivation significantly impaired participants' performance on both the easy and difficult versions of the Psychomotor Vigilance Test task, as well as accuracy but not reaction speed in the Go/No-Go task. Accuracy in the difficult version of the Flanker task and the 2-back task was also lower in the no-nap condition, while reaction speed in the 2-back task but not the Flanker task was reduced without a nap in both the easy and difficult versions. Moreover, subjective sleepiness was significantly increased after nap deprivation, but moods remained unaffected in the no-nap condition. These findings contribute to current research suggesting that effects of a midday nap on task performance depend on the cognitive domain as well as task difficulty. Our study highlights the importance of considering task characteristics to evaluate the benefits of a regular midday nap in practical working life.