Theoretical and Empirical Analysis of Circadian Rhythm Disruption as a Mediator of Cardiometabolic Disease Risk in Urban Nigerian Night Workers

Circadian rhythm disruption has emerged as a theoretically coherent but empirically under-examined mechanism linking night shift work to cardiometabolic disease, particularly in African urban populations whose occupational epidemiology differs from Western counterparts. This study theoretically grounded and empirically tested a circadian disruption mediation model of cardiometabolic risk among night workers in two Nigerian cities, Abuja and Lagos, making an original theoretical contribution to chronobiology-cardiometabolic physiology. A cross-sectional design with mechanistic depth recruited 100 permanent night workers and 100 day workers matched by age, sex, and body mass index from hospital, security, and transportation sectors. Circadian rhythm disruption was objectively characterised by wrist actigraphy over fourteen days and salivary melatonin onset timing. Cardiometabolic risk indices included 24-hour ambulatory blood pressure, fasting glucose, insulin resistance, lipid profile, and high-sensitivity C-reactive protein. Cortisol diurnal profiles and core body temperature rhythms were assessed. A theoretically derived mediation model was tested using structural equation modelling. Results confirmed that circadian rhythm disruption fully mediated the association between night work and elevated blood pressure, while partially mediating insulin resistance and dyslipidaemia associations. Melatonin timing misalignment was the strongest circadian marker predicting cardiometabolic outcomes. The effect was amplified in workers above age 40. This study provides original theoretical and empirical evidence for a circadian-cardiometabolic mechanism in Nigerian night workers. Chronobiologically informed shift scheduling policies are recommended. Keywords: circadian rhythm, night shift, cardiometabolic risk, melatonin, Nigerian workers.