Association of Evening Chronotype with Poor Control of Type 2 Diabetes: Roles of Sleep Duration and Insomnia Level

Background: Evening chronotype is usually associated with insomnia and short sleep duration. Objectives: To investigate the independent association of chronotype with diabetes control. Methods: In this cross-sectional study, 140 patients with type 2 diabetes were studied. The insomnia score was examined by a 7-item questionnaire. Also, chronotype was assessed by a 19-item questionnaire, and using the questionnaire, the patients were divided into three groups of morning, intermediate, and evening. This questionnaire has been developed for evaluating the preference for performing mental and physical activities at a special time of day. The Multivariate hierarchical analysis was applied for investigating the independent association of chronotype and glycated hemoglobin (HbA1c). Results: The fasting blood glucose and HbA1c levels were significantly different across all the three chronotype groups such that it had the highest value in the evening group and the lowest value in the morning group (FBS = 164.5 ± 34.1 mg/dL and HbA1c = 8.7% ± 1.7, in the evening group, and FBS = 132.7 ± 23.1 mg/dL and HbA1c = 6.9% ± 0.4 in the morning group, P < 0.001). The morning group had longer sleep duration and less insomnia than other groups. Results of the hierarchical regression analysis showed that the chronotype explained 28.4% of the variance of HbA1c. Results of the final model demonstrated that the chronotype had a relationship with HbA1c, independent of body mass index (BMI), time of going to bed, and insomnia score. Conclusions: Evening chronotype is associated with poorer control of diabetes, independent of BMI and sleep variables.