Objective To explore the relationship between chronotype preference (morningness-eveningness) and sleep quality among Chinese adolescents.
Methods The data of the study were from National Youth Mental Health Survey conducted by Institute of Psychology of Chinese Academy of Sciences in 2009 in six provinces across China. In the survey, 3 944 sixth grade elementary school students and high school students with a mean age of 15.06 ± 2.49 years and approximately 1 : 1 gender ratio were selected using stratified multistage cluster random sampling and surveyed with Morningness/Eveningness Scale for Children (MECS), Pittsburgh Sleep Quality Index (PSQI) and The Center for Epidemiological Studies Depression Scale (CES-D).
Results There was a significant gender difference in MESC score (t = 2.89, P < 0.01). The MESC score was 32.02 ± 4.61, 29.65 ± 4.21, and 29.13 ± 4.08 for the students aged 10 – 13, 14 – 17, and 18 – 22 years, with a significant difference (P < 0.01).The adolescents with eveningness preference (evening-type) had significantly higher both global PSQI score (6.64 ± 2.68 vs. 3.96 ± 2.40) and seven PSQI component scores than those with morningness preference (morning-type) (all P < 0.05). The evening-type adolescents went to bed later than morning-type adolescents on both school days and weekends (P < 0.05) and they also tended to get up later than morning-type adolescents on weekend (P < 0.05）; the evening-type adolescents had shorter sleep time on school days than morning-type students (P < 0.05). There was no significant difference between evening-type and morning-type adolescents in the weekday wake-up time and weekend sleep time. Hierarchical regression analysis showed that among the adolescents, depression partially mediated the relationship between chronotype preference and sleep quality, with a mediated effect value of 0.13 and the ratio of mediated effect to total effect was 39.6%.
Conclusion Evening-type adolescents have higher PSQI scores, worse sleep quality and suffer more from inadequate sleep in school days; chronotype preference has both direct and indirect effect via depression on sleep quality among adolescents.
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