Circadian Disruption in Nurses Working Night Shift: What We Know,What We Miss

Walk into a hospital unit at 3 a.m. Bright lights are on and nurses are performing tasks demanding sustained attention and precision. Operationally, the system works. Biologically, it does not. The circadian rhythm responds to a light-dark cycle that anticipates darkness at night. Night-shift work inverts this relationship due to the use of artificial light. Exposure to light-at-night (LAN) shifts and disrupts the circadian timing of key biological processes, making physiological systems inefficient (Salmond et al., 2025). Critically, even after consecutive night shifts, the system adapts only partially, leaving many circadian-dependent bodily processes aligned to daytime, putting nurses in a persistent state of circadian misalignment.

Consequences from circadian misalignment span sleep, occupational performance, and long-term health. Night-shift nurses experience reduced and fragmented sleep and excessive sleepiness (Gu et al., 2024). Due to mismatch between circadian timing and task demands, cognitive performance declines across the night, reducing vigilance, slowing reaction times, and increasing fatigue (Ulupınar, 2025). Beyond acute effects, circadian disruption and LAN has been linked to reproductive dysfunction, metabolic dysregulation, and cancer-related pathways, reflecting its systemic impact across physiological processes (National Toxicology Program, 2021).

A notable barrier to effective interventions is a research gap in how light exposure is measured. Many studies rely on ambient illuminance or self-reported exposure, neither of which captures the biologically relevant stimulus. Circadian responses depend on dosage—intensity, timing, duration, and retinal exposure, not simply room illumination (Murukesu et al., 2025). As a result, inconsistencies in field findings are likely driven by measurement imprecision rather than absence of effect. Standardized personal light dosimetry and biologically meaningful metrics remain a critical unmet need.

Interventions have focused on lighting and behavioral strategies, with mixed but promising results. Bright and spectrally tuned lighting systems can improve alertness and support circadian health, while off-shift behavioral changes, including timed light exposure and meal timing, may help preserve melatonin, improve sleep, and support metabolic regulation (Moreno et al., 2022). However, LAN exposure needs to be accurately quantified, translating that knowledge into both biologically effective and practically deployable interventions. Until then, occupational health nurses can support circadian health by educating management and nurses on LAN exposure, urging nurses and managers to keep shifts between midnight and 5 a.m. to no more than three times per week, teaching use of timed and strategic daylight exposure to support circadian alignment, encouraging shift schedules that support individual sleep preferences, and promoting regular health screenings and overall wellness through good sleep, nutrition, and regular exercise (Hittle & Wong, 2022; National Institute for Occupational Safety and Health, 2015).