OBJECTIVES: This review examines how nighttime noise and irregular schedules influence circadian and endocrine regulation. It introduces a conceptual multilevel model to explore how these exposures may accumulate over time and contribute to long-term health risks.
METHODS: A scoping narrative review was conducted following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses principles in PubMed, Scopus, Web of Science and Embase (1992-2024), including human studies on nighttime noise and shift work. Eligible studies involved adults and reported circadian, hormonal, metabolic or chronic disease outcomes. Twenty-five studies were synthesised using direction-based vote counting due to heterogeneity because meta-analysis was not feasible. The tally reflected the direction of effects rather than statistical significance. Risk-of-bias assessments informed interpretation, but not exclusion. Findings were integrated into a multilevel model integrating exposure, physiological mediation and cumulative effects.
RESULTS: Nighttime noise and rotating night duties shifted melatonin timing and reduced sleep continuity. Studies reported increased fasting glucose, decreased insulin sensitivity and unfavourable lipid profiles in groups exposed to these work periods. Several investigations described an increase in cardiometabolic load amongst long-term night-duty workers. In the simulation scenarios, the model followed these findings and produced circadian and metabolic changes that increased across repeated exposure cycles.
CONCLUSIONS: This review proposes and illustrates a dynamic framework for understanding how nighttime noise and shift work may contribute to circadian and metabolic disruption over time. Its exploratory nature reflects heterogeneous evidence and a scoping design. The findings should be interpreted without causal inference.
