Shifting Perspectives: Multidimensional Insights into Exposure to Night-Shift Work

The increasing prevalence of night-shift work across various industries poses significant health risks due to its disruption of the circadian rhythm, which is essential for regulating bodily functions. This disruption elevates the risk of sleep disorders and chronic diseases, including obesity, diabetes, and cardiovascular conditions. Night-shift workers often engage in unhealthy behaviors, such as substance abuse and physical inactivity, compounding these risks. The International Agency for Research on Cancer (IARC) classifies shift work that disrupts circadian rhythms as probably carcinogenic, underscoring the need for precise cohort studies to clarify the health implications of shift work. This thesis aims to enhance the characterization of shift work disruption, identify intervention targets, and provide insights to mitigate adverse effects, ultimately improving the quality of life for shift workers. Chapter 1 introduces a theoretical framework for assessing shift work exposure, aligning with the IARC's recommendations, and presents the Klokwerk study, focusing on female healthcare workers categorized into night-shift and day workers. The study employs comprehensive data collection methods, including blood sampling, questionnaires, and sensor monitoring, to investigate the health effects of shift work. Chapter 2 presents a systematic literature review of the association between shift work and metabolic risk factors, emphasizing the need for high-quality studies to reinforce existing evidence. While the metabolic health consequences of shift work are documented, a systematic synthesis had been lacking. The review found strong evidence linking shift work to increased body weight/BMI and impaired glucose tolerance but insufficient evidence for other metabolic risk factors, attributed to inconsistencies in findings. It highlights the need for further longitudinal studies and suggests investigating the mediating role of lifestyle behaviors. Chapter 3 discusses omics techniques and the mechanisms linking shift work to health, advocating for an integrated exposome approach. Recognizing shift work as a complex mix of factors—such as light exposure and altered sleep patterns—this chapter proposes innovative methods like mobile apps and OMICS platforms to assess these influences. Chapter 4 examines external factors, including lifestyle elements like diet and physical activity among female healthcare workers. The Klokwerk study revealed that night-shift workers had similar physical activity and caloric intake on non-night shifts but increased daylight exposure, particularly at noon. Differences in diet, physical activity, and daylight exposure were primarily attributed to changes in exposure patterns, underscoring the significance of time-resolved measurements in night-shift work research. In Chapter 5, the potential of the biomarker sCD36 as an indicator of chronic circadian disturbance is explored. Despite prior research suggesting its potential, the study found no significant differences in plasma levels between day and night-shift workers, indicating that further investigation in larger cohorts may be necessary. Part III of the thesis examines specific health implications in Chapters 6 and 7. Chapter 6 focuses on the effects of shift work on circulating lipoproteins and metabolites, revealing unfavorable fatty acid profiles in night-shift workers. Chapter 7 analyzes the broader Nightingale cohort study, highlighting that while night-shift work was not significantly linked to self-reported sleep quality, it was associated with higher odds of sleep medication usage. Chapter 8 serves as the general discussion, summarizing key findings and discussing methodological considerations. It emphasizes the need for enhanced exposure assessments and identifying markers of chronic circadian disruption. Understanding the health implications of shift work is crucial for developing effective interventions and improving the quality of life for shift workers, necessitating future research on detailed exposure measurements and the relationship between disrupted circadian rhythms and health outcomes.