RESUMO
BACKGROUND/OBJECTIVES: Later chronotype has been associated with poorer glycemic control in type 2 diabetes. It is unclear whether this is a direct relationship, or if personality factors or social jetlag ([SJL], ie, chronic circadian misalignment reflecting the discrepancy between the entrained phase of the circadian clock and socially-determined behavioural cycles) play a role. This study aimed to determine the relationships among chronotype, SJL, personality factors and glycemic control in type 2 diabetes, independently of sleep disturbances and daily caloric distribution. METHODS: In sum, 252 type 2 diabetes patients attending an annual review outpatients' clinic completed questionnaires, including the Munich Chronotype Questionnaire to assess chronotype and SJL, the Pittsburgh Sleep Quality index (PSQI), the Big Five Personality Inventory and the Center for Epidemiologic Studies Depression Scale. Chart review provided information on diabetes duration, Hemoglobin A1c (HbA1c), body mass index (BMI) and other clinical variables. Caloric intake was assessed via 24-h dietary recall. RESULTS: Hierarchical linear regression revealed that SJL, but not chronotype or personality factors, was a significant predictor of HbA1c levels (ß = 0.16, p < 0.05). There was a significant relationship between later chronotype and HbA1c levels, but only in patients who had more than 90 min SJL (r = 0.51, p = 0.002). Younger age was associated with a higher HbA1c (r = -0.23, p < 0.001), and this effect was partially mediated through SJL (Pm = 0.22). CONCLUSIONS: We identify SJL as a novel factor that may impact on glycemic control in type 2 diabetes. Further study is needed to determine whether interventions aimed at reducing SJL may lead to improvements in glycemic control.