To our knowledge, this is the first research to analyze the trajectory of multiple HRBs in college students, and further analyze its relationship between chronotype, sleep duration. Our study found that the trajectories of multiple HRBs over time can be divided into four patterns: healthy group, increasing group, decreasing group and unhealthy group. Aberrant sleep duration, including short sleep duration and long sleep duration were both associated with high-risk trajectories. The results of the study also identified a significant association between E-types and the trajectory of high-risk trajectories of HRBs.
This research is the first to examine the interdependence trajectories of four HRBs:smoking, alcohol use, low physical activity, smartphone addiction. As expected, the vast majority of people belong to the healthy group (61.0% of sample), while the unhealthy group only account for 7.4% of the total population. Similar percentages of adolescents in high-risk groups were found in the Mobile Youth Study, in which approximately 11% of children aged 12 to 18 exhibited increasing high risk in all three areas, including substance use, conduct problems, and sexual risk taking [26]. However, the study by Zhang et al. through the follow up of 1,974 children aged 7 to 9, the fitting results of four life style (screen time, physical activity, sleep duration and beverage intake) trajectories showed that persistent healthy groups accounted for 39.9%, while 17.7% of children were persistent unhealthy groups [27]. The large differences in grouping may be due to the differences in HRBs included in the studies and the fact that the subjects came from different ages, changing one behaviour will affect the prevalence of others [28].
The study found that about 10.1% of college students reported E-types, which was below the 20.5% of students from 8 major Lebanese universities who reported E-types [29]. Compared with M-type, Evening-type was associated with three high-risk HRBs classes. Children are typically M-types, gradually becoming E-types after entering puberty, and teenagers around the age of 20 sleep at the latest [30]. Some previous studies have found that those with later bedtimes had some lifestyle habits that might delay bedtimes, increase depressive symptoms, and lead to health hazards [31]. During adolescence, there is a shift in biologic preference to later sleep timing, which often conflicts with socially prescribed scheduling demands, such as early school start times [32]. It has been speculated that nocturnal time types may affect gene expression, metabolism, immunoendocrine function, and behavior due to the chronic mismatch between internal physiological time and externally imposed time for work and social activities [33]. Previous studies have found that a later phenotypes may be more associated with externalized behaviors, such as risk-taking and substance use [34]. Since these behaviors are more likely to occur at night times with less parental supervision, and the E-types provides greater opportunities for participation in such behaviors [35], it should not be surprising that the association with E-types and relatively high-risk trajectories. Furthermore, evening chronotype may contribute to HRBs through impairments in emotion regulation, executive function, response inhibition, and decision making [36-37].
Of particular note in this research is the association between sleep duration and the trajectory of HRBs. We observed that about 35.5% of students had short sleep, 7.3% of students reported long sleep, which was different from the detection rate of Shandong Adolescent Behavior and Health Cohort [29]. Using data from the Fairfax County Youth Survey, Owens found that students with sleep insufficiency were significantly more likely than respondents without sleep insufficiency to report drug use and delinquency [38]. Based on data from the Project for the Health of Adolescents in Southern Taiwan, the results indicated that both short and long sleep duration were significantly associated with having suicidal and drinking alcohol every week [39]. Previous studies have mainly found the effect of sleep duration on HRBs through cross-sectional studies. However, our research found that not only short but long sleep also affected HRBs trajectories in a cohort study. Regarding the mechanism that leads to the association between sleep duration and HRBs, based on the evidence from a systematic review, suggests that comparing various sleep duration against an “optimal” sleep duration allows non-linear relationships to be observed. U-shaped relationships between sleep duration and risk-taking where both short and long sleep duration are associated with heightened risk-taking [40]. Epidemiological studies have demonstrated that short sleep and sleep disturbance are associated with subsequent impairment in multiple domains of psychosocial and cognitive functioning, delinquency, impulsivity, substance use, and depression [41-42].
Strengths and limitations/implications and sleep research perspectives
These findings contribute to the literature is that we use a latent class growth model to fit the trajectory of the HRBs among college students. The combined analysis of relationship between multiple HRBs rather than single HRBs and chronotype, sleep duration is more in line with the needs of real-world research, which can reflect the dynamic changes and influencing factors of HRBs in adolescence. Second, we used a cohort study to carry out a follow-up investigation and collected data on various HRBs of college students many times, which makes the results more convincing. As far as we know, this is the first research to report the association between E-types, aberrant sleep duration and longitudinal HRBs. The highlight of this research is to explore the influence of circadian rhythm on multiply HRBs, so as to reveal the influence of circadian rhythm on human health.
Despite the above advantages, there is no denying that this research has limitations in the following aspects: although we have adopted a self-reporting scale that has been fully verified and used, reporting bias is still unavoidable. In addition, this research was conducted in two specific geographic regions of China, and the research results may not be applicable to young people who have been extrapolated to various parts of China, which needs to be verified by national representative research in the future.