Effects of emotional labor and sleep quality on depression in older apartment security workers in Korea: a cross-sectional study.

Insulin resistance is a pathological condition characterized by inadequate tissue response to normal insulin action, causing impaired glucose uptake and metabolism []. Insulin resistance affects approximately 26.5% of the global adult population [], representing the central pathophysiological mechanism underlying Type 2 diabetes, and substantially increases the risk of cardiovascular diseases, obesity, hepatic steatosis, and metabolic syndrome []. This asymptomatic metabolic dysfunction precedes overt Type 2 diabetes by 10~15 years [], during which progressive beta cell compensation masks deteriorating glucose homeostasis []. In Korea, the adult prevalence of insulin resistance is approximately 23.3% [], while metabolic syndrome affected one-third of the adult population as of 2020, reflecting a 22.5% increase over the past two decades []. Insulin resistance remains clinically silent until complications manifest []; thus, identifying at-risk populations and modifiable predictors is critical for preemptive intervention. Among the occupational factors that may influence insulin resistance risk, shift work has emerged as a significant exposure, affecting approximately 25% of the global workforce and many Korean workers across the manufacturing, healthcare, transportation, and service sectors [,]. Shift work disrupts the alignment between endogenous circadian rhythms and external environmental cues, causing chronic circadian discordance []. This desynchronization triggers multiple pathophysiological pathways that affect diverse health outcomes. At the metabolic level, disrupted suprachiasmatic nucleus signaling impairs vasopressin-mediated glucose uptake, while suppressed nocturnal melatonin secretion reduces pancreatic insulin synthesis []. Beyond glucose metabolism, circadian disruption dysregulates lipid metabolism, promotes systemic inflammation through elevated pro-inflammatory cytokines (TNF-α, IL-6), and impairs vascular endothelial function [,]. These mechanisms collectively increase susceptibility to insulin resistance, cardiovascular diseases, inflammatory disorders, and metabolic syndrome [,]. A recent meta-analysis of over 235,800 participants demonstrated that shift workers exhibited a 30% increased risk of Type 2 diabetes compared with the risk among day workers []. Additionally, an umbrella review has confirmed elevated risks of obesity (25% increase), hypertension (30% increase), and mental health disorders (32%~42% increase), establishing shift workers as a particularly vulnerable occupational group []. Previous research on insulin resistance in shift workers has revealed multiple potential risk factors. Demographic factors such as age and sex have shown varying associations, with some cohorts reporting an elevated insulin resistance risk among women shift workers, whereas others have suggested context-dependent patterns [,]. In addition, lifestyle factors, including poor dietary habits, physical inactivity, and irregular meal timing, are associated with a high prevalence of insulin resistance []. Metabolic parameters, particularly obesity and metabolic syndrome, demonstrate robust associations with insulin resistance; however, the temporal relationships remain debated []. Emerging evidence suggests that psychological stress contributes to the development of insulin resistance [] and depressive symptoms have also been positively associated with increased insulin resistance []. Furthermore, quality of life, as a multidimensional indicator of physical and psychological well-being [], was adjusted for to minimize confounding from general health status.