Objectives Previous epidemiological studies have indicated that solar ultraviolet B radiation (UVR) may have a protective effect on breast cancer. However, the evidence remains inconclusive. Despite the fact that outdoor work history may be considered a reliable measure of long-term UVR exposure, objective information on lifetime employment has not been included in previous investigations focusing on breast cancer. To address this issue, we explored the association between occupational UVR exposure and female breast cancer, including subtypes.
Methods A total of 38 375 women under the age of 70 years were identified with primary breast cancer using the Danish Cancer Registry. Five female controls born on the same year, alive and free of breast cancer at the time of diagnosis of the index case, were randomly selected from the Danish Civil Registration System. The Danish Supplementary Pension Fund Register was used to retrieve full employment history, and a job exposure matrix was used to assess occupational UVR exposure. Conditional logistic regression with adjustment for important confounders was used to estimate the OR.
Results We observed no overall association between occupational UVR exposure and breast cancer. After the age of 50 years, longer duration of UVR exposure (≥20 years: OR=0.83, 95% CI 0.75 to 0.92) and highest cumulative exposure (OR=0.89, 95% CI 0.83 to 0.95) were inversely associated with risk. Our results did not reflect any notable risk difference by oestrogen receptor status.
Conclusions This study indicates an inverse association between long-term occupational UVR exposure and late-onset breast cancer. This finding needs further attention in future occupational studies.
- occupational health
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Contributors JEP contributed substantially to the conception of the study, performed the analyses, interpreted the results and wrote the manuscript. KS-L and MA contributed to the conception of the study, interpreted the results and revised the manuscript critically. JH was a key contributor in the design process of the study and the analyses that were undertaken, and revised the manuscript critically for important intellectual content. All authors have approved the final version to be published and are accountable for all aspects of the work.
Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.
Competing interests None declared.
Patient consent for publication Not required.
Ethics approval The research has been notified to the Danish Data Protection Agency and it has been carried out in concordance with the requirements relating to the use of non-sensitive data about participants. As an ethical approval for undertaking purely register-based research is not needed in Denmark, this was not attained.
Provenance and peer review Not commissioned; externally peer reviewed.
Data availability statement No data are available.
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