Sleep, circadian disruption and breast cancer risk in working women: A narrative review

Introduction: Circadian rhythms play a key role in regulating hormonal secretion, immune function, metabolism, and cell-cycle control. Disruption of these rhythms due to artificial light at night (ALAN), sleep disturbances, and shift work has been increasingly implicated in breast cancer risk, particularly among working women.
Objective: This narrative review summarizes current evidence on the association between circadian rhythm disruption, sleep disturbances, and breast cancer, with emphasis on biological mechanisms and public health relevance.
Methods: A narrative review of English-language literature published between 2015 and 2025 was conducted using PubMed and Google Scholar. Epidemiological, clinical, and experimental studies examining ALAN exposure, shift work, sleep characteristics, circadian misalignment, and breast cancer outcomes were included.
Results: Most epidemiological studies report a positive association between night shift work, prolonged ALAN exposure, poor sleep quality, and increased breast cancer risk. Proposed mechanisms include melatonin suppression, dysregulation of estrogen signaling, altered clock gene expression, immune dysfunction, and impaired DNA repair. Experimental evidence supports the oncostatic role of melatonin through estrogen receptor modulation, cell-cycle arrest, apoptosis induction, and immune enhancement. However, heterogeneity in study design, exposure assessment, and outcome measures, along with reliance on observational data, limits causal interpretation.
Conclusion: Circadian disruption and sleep disturbances may represent modifiable risk factors for breast cancer, especially in occupational settings involving night work. Strategies to improve circadian hygiene, optimize shift schedules, and reduce ALAN exposure could contribute to breast cancer prevention. Further well-designed longitudinal and mechanistic studies are required to strengthen causal inference and guide targeted chronopreventive and chronotherapeutic approaches.