The evening type was associated with higher levels of depression during the school day but not during the summer vacation
Authors: Wan Zhenyu , Xiao Ling , Wang Gaohua 
Published: March 2023

Abstract
With the increasing prevalence of sleep problems and depression, the bidirectional relationship between sleep and depression has been widely concerned by researchers. People can be divided into different chronotypes according to individual differences, and their risk of depression also varies significantly due to the different sleep habits of different chronotypes. Morning type is a better lifestyle pattern and has been advocated as a protective factor for depression. However the evening type is associated with a higher risk of depression, either possibly due to their significantly delayed bedtime or due to the large misalignment between social rhythms and evening type's biological rhythms during the workday, which affects the evening type's sleep behavior and leads to a higher risk of depression. However, the characteristics and differences of sleep behavior and depression degree among different chronotypes under different social rhythms, and whether the evening type has higher depression degree under different social rhythms are rarely investigated.
Objective:
The purpose of this study was to explore the relationship between evening and morning types and depression and anxiety under different social rhythms, the differences and changes of sleep behaviors and levels of depression and anxiety in different chronotypes
under different social rhythms were also described.
Participants and methods:
The follow-up study was conducted one month after the start of the summer vacation in 2021 (from August 1 to August 8). We randomly selected a university in the area, survey invitations were distributed to students outside their graduation year through WeChat and OICQ, and they were free to choose the form of online interview or questionnaire. A total of 1048 people clicked on the survey link to learn about the research content, and 608 people agreed to be surveyed and participate in the follow-up study. A total of 450 people completed the first survey, after the inclusion and exclusion criteria were applied, 412 individuals were left in the study group. An online questionnaire invitation was sent to 412 students 3 months later (Two months after school started), and 391 students completed and were finally included in the statistical analysis.
Results:
There were 178 males (45.5%) and 213 females (54.5%) with an average age of 20 years. Morning type 58 (14.8%), intermediate type 262 (67.0%), evening type 71 (18.2%). During the summer vacation: there were significant differences in levels of depression and anxiety (p <0.001, p <0.001), bedtime (p <0.001), sleep onset latency (p <0.001) and sleep debt (p <0.001) among different chronotypes. But there were no significant differences in sleep duration (p=0.126) and daytime sleepiness (p=0.053). After a pairwise comparison, we found that morning type had the earliest bedtime (p =0.003, p <0.001) and significantly lower levels of depression (p <0.001) and anxiety (p <0.001) than other chronotypes. The evening type had the latest bedtime (p <0.001, p <0.001), but the levels of depression and anxiety was not significantly different from that of the intermediate type (p =0.086，p =0.64). During school: There were significant differences in depression and anxiety levels (p <0.001, p <0.001), bedtime (p <0.001), sleep duration (p <0.001), sleep onset latency (p <0.001), sleep debt (p <0.001) and daytime sleepiness (p <0.001) among different chronotypes. After a pairwise comparison, we found that compared with other chronotypes, morning type had the earliest bedtime (p <0.001, p <0.001), the longest sleep duration (p <0.001, p <0.001), and the lowest daytime sleepiness (p <0.001, p <0.001). They also had the lowest levels of depression (p <0.001, p <0.001) and anxiety (p <0.001, p <0.001). On the contrary, evening type had the latest bedtime (p <0.001, p <0.001), the shortest sleep duration (p <0.001, p <0.001), and the highest daytime sleepiness (p <0.001, p <0.001) compared with other chronotypes. They also had the highest levels of depression (p <0.001, p =0.004) and anxiety (p <0.001, p <0.001).
Conclusion:
Under the two common social rhythms, morning type has better sleep behavior, lower levels of depression and anxiety, which is worthy of further promotion. The evening type was significantly associated with higher levels of depression and anxiety during the school but not during the summer vacation. Postponing the social start time of workdays may effectively prolong the sleep duration of evening types and reduce the risk of depression and anxiety.