Chronotype, Unhealthy Lifestyle, and Diabetes Risk in Middle-Aged US Women A Prospective Cohort Study

Background: Evening chronotype may promote adherence to an unhealthy lifestyle and increase type 2 diabetes risk. Objective: To evaluate the role of modifiable lifestyle behaviors in the association between chronotype and diabetes risk. Design: Prospective cohort study. Setting: Nurses' Health Study II. Participants: 63 676 nurses aged 45 to 62 years with no history of cancer, cardiovascular disease, or diabetes in 2009 were prospectively followed until 2017. Measurements: Self-reported chronotype using a validated question from the Morningness-Eveningness Questionnaire. The lifestyle behaviors that were measured were diet quality, physical activity, alcohol intake, body mass index (BMI), smoking, and sleep duration. Incident diabetes cases were self-reported and confirmed using a supplementary questionnaire. Results: Participants reporting a "definite evening" chronotype were 54% (95% CI, 49% to 59%) more likely to have an unhealthy lifestyle than participants reporting a "definite morning" chronotype. A total of 1925 diabetes cases were documented over 469120 person-years of follow-up. Compared with the "definite morning" chronotype, the adjusted hazard ratio (HR) for diabetes was 1.21 (CI, 1.09 to 1.35) for the "intermediate" chronotype and 1.72 (CI, 1.50 to 1.98) for the "definite evening" chronotype after adjustment for sociodemographic factors, shift work, and family history of diabetes. Further adjustment for BMI, physical activity, and diet quality attenuated the association comparing the "definite evening" and "definite morning" chronotypes to 1.31 (CI, 1.13 to 1.50), 1.54 (CI, 1.34 to 1.77), and 1.59 (CI, 1.38 to 1.83), respectively. Accounting for all measured lifestyle and sociodemographic factors resulted in a reduced but still positive association (HR comparing "definite evening" vs. "definite morning" chronotype, 1.19 [CI, 1.03 to 1.37]). Limitations: Chronotype assessment using a single question, self-reported data, and homogeneity of the study population. Conclusion: Middle-aged nurses with an evening chronotype were more likely to report unhealthy lifestyle behaviors and had increased diabetes risk compared with those with a morning chronotype. Accounting for BMI, physical activity, diet, and other modifiable lifestyle factors attenuated much but not all of the increased diabetes risk.