[Independent and joint effect of chronotype and sleep duration on self-rated health in medical students].

Objective: To investigate the independent and joint effects of chronotype and sleep duration on self-rated health in medical students. Methods: A cross-sectional study was conducted in 1 526 medical students selected through proportional stratified cluster random sampling from a medical university in Zhejiang province. A questionnaire survey was conducted to collect the information about their basic demographic characteristics, chronotype, sleep duration, and other lifestyle factors such as midnight snack, sedentary behavior, physical activity, meal time, and self-rated health. The independent and joint effects of chronotype and sleep duration on self-rated health were assessed by logistic regression model after controlling for confounding variables. Results: The numbers of the students with evening chronotype, neutral chronotype, and morning chronotype were 664 (43.5%), 442 (29.0%), and 420 (27.5%), respectively. Among the medical students, 42.8% (653) had poor self-rated health. Compared with those with the morning chronotype, the adjusted ORs for those with neutral chronotype and evening chronotype were 1.69 (95%CI: 1.23-2.31) and 2.43 (95%CI: 1.81-3.26), respectively, trend test P<0.001. Compared with those with sleep duration of 8 h or above per night, the adjusted ORs for those with sleep duration of 7 and ≤6 h per night were 1.40 (95%CI: 1.07-1.84) and 2.38 (95%CI: 1.69-3.37), respectively, trend test P<0.001. In the joint effect, compared with those with the morning chronotype and sleep duration of 8 h or above per night, the adjusted OR for those with evening chronotype and sleep duration of ≤6 h per night was 6.53 (95%CI: 3.53-12.09). Conclusions: Both evening chronotype and insufficient sleep were associated with increased odds of poor self-rated health in medical students, and they had joint effects. Therefore, it is necessary to promote early to bed, early to rise and adequate sleep in medical student to maintain their health.