Evaluating Weekly Circadian Misalignment and the Role it Plays in Type 2 Diabetes Disease Management

Background Type 2 diabetes (T2D) is a chronic condition and poorer glycemic control in T2D increases the risk of debilitating complications. Sleep and sleep timing have been implicated in both T2D disease risk and management. Chronotype, the behavioural manifestation of phase of entrainment, and social jetlag (SJL), the misalignment between external social time and internal biological time, have been associated with poorer metabolic health. The primary aim of this thesis was to determine how phase of entrainment and living against the circadian clock can influence T2D disease management, with the intention of guiding potential behavioural or educational interventions to improve T2D disease management. Methods and Results Chapter 2 was a cross-sectional study which revealed that SJL predicted poorer glycemic control in participants with T2D, while chronotype and personality factors were not significant predictors. A novel interaction between chronotype, SJL and glycemic control was identified; a positive association between later chronotype and HbA1c was only identified in those with the most SJL. Chapter 3 assessed additional measures of sleep timing variability and metabolic health. This work demonstrated that many measures of circadian misalignment may not measure the same construct. SJL and sleep end variability were moderately associated; however, variability in midsleep, sleep onset and actual sleep duration were not associated with SJL. Furthermore, variability in midsleep, sleep onset and actual sleep duration showed an inverse association with HbA1c in a group of people with well controlled diabetes, suggesting that lower variability was associated with higher HbA1c levels. Why exactly this occurs is unknown, it may be reliant on the characteristics of the sample. Chapter 4 included two studies which investigated the association between SJL and stress. Study 1 was a cross-sectional study which revealed that SJL was not a significant predictor of general perceived stress or work-related psychosocial stress. Study 2 was an experimental study which demonstrated that SJL did not result in greater reactivity to a physiological stressor. These studies combined suggest that stress does not mediate the effect of SJL on glycemic control or other indicators of metabolic health. Chapter 5 described weekly sleep offset differences in a large sample of UK adults. Interestingly, older participants who were not working displayed weekday to weekend day sleep offset differences, albeit to a lesser degree than younger participants. Chapter 6 qualitatively assessed sleep timing among participants with T2D who were either retired or not currently working. Reducing circadian misalignment may be more feasible among individuals without the daily constraints that come with a regular work schedule. Reflexive thematic analysis of semi-structured interviews revealed that social factors such as quality of TV programs and a desire to maintain a sense of normality when not working led to fluctuating sleeping patterns. Derived zeitgebers from family members also played a role. Those with consistent sleeping patterns had formed healthy habits, had ownership over the environment before bed and good sleep hygiene. They also had some unavoidable curtailments every morning that helped them to form this schedule. Conclusion The current findings highlight how common circadian misalignment is and how it may impact T2D management. The findings also provide some rich information on what factors can influence sleep timing beyond work schedules. This paves the way for developing some behavioural and psychoeducational interventions designed to reduce circadian misalignment among those with T2D. This could then reduce the risk of debilitating complications