This review argues that night shift work may raise breast cancer risk through and related biological pathways, while informing more precise risk stratification.
Evidence
This narrative review synthesizes mechanistic hypotheses, putative biomarkers, and case-control and cohort evidence on breast cancer risk in female night shift workers.
Caveat
Because it is a review of heterogeneous observational and mechanistic evidence, exposure misclassification and confounding limit any firm causal conclusion.
Simplified
The increasing prevalence of night shift work (NSW) in our current professional landscape has raised significant public health concerns, particularly regarding its potential role in breast cancer (BC) development among women. Recognized by the International Agency for Research on Cancer (IARC) as a probable human carcinogen, NSW is believed to contribute to carcinogenesis primarily through induced by exposure to light at night. This review explores three key areas: (1) the biological mechanisms potentially linking NSW to BC, including suppression, oxidative stress, immune dysregulation, chronic inflammation, clock gene alterations, epigenetic modifications, telomere shortening, estrogen signaling disruption, vitamin D deficiency, and gut microbiome imbalance; (2) the emergence of novel putative biomarkers with might be relevant to early detection and precision risk analysis; and (3) the latest epidemiological evidence from case-control and cohort studies evaluating BC risk in female night shift workers, while considering the heterogeneity caused by exposure misclassification and other confounding factors. Altogether, these insights underscore the importance of integrating mechanistic, molecular, and epidemiological data, not only to deepen our understanding of the strength and nature of the relationship between NSW and BC, but also to support a precision medicine framework. This integrated approach is essential for improving individual risk stratification, guiding occupational health policies, and developing targeted preventive strategies for high-risk workers.
Key numbers
8.58
Increased Risk of Breast Cancer
Odds ratio for breast cancer risk associated with ≥10 years of night shift work in Mexican women.
53%
Significant Association
Percentage of studies reporting a positive association between night shift work and breast cancer risk since 1996.
↑ 8-OH-dG
Elevated Oxidative Stress
Marker of oxidative DNA damage found higher in night shift workers compared to day shift workers.
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Circadian Biology