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Epidemiology
Research
A cross-sectional study of breast cancer biomarkers among shift working nurses
  1. Annie R Langley1,2,
  2. Charles H Graham2,3,
  3. Anne L Grundy1,2,
  4. Joan E Tranmer1,4,
  5. Harriet Richardson1,2,
  6. Kristan J Aronson1,2
  1. 1Department of Community Health and Epidemiology, Queen's University, Kingston, Canada
  2. 2Division of Cancer Care & Epidemiology, Queen's Cancer Research Institute, Queen's University, Kingston, Canada
  3. 3Department of Anatomy and Cell Biology, Queen's University, Kingston, Canada
  4. 4School of Nursing, Queen's University, Kingston, Canada
  1. Correspondence to Dr Kristan J Aronson; aronson{at}queensu.ca

Abstract

Objectives In 2007, the International Agency for Research on Cancer classified long-term shift work as a probable carcinogen, with the strongest evidence for breast cancer. One proposed mechanism involves night-time light exposure and decreases in melatonin, a circadian rhythmic hormone. It is hypothesised that melatonin influences patterns of sex hormone production that in turn influence breast cancer risk. This study sought to investigate the relationships of shift work history, 6-sulfatoxymelatonin (aMTs-6, the primary melatonin metabolite) and sex hormone levels among shift working nurses.

Design This is a cross-sectional biomarker study.

Setting 94 premenopausal nurses who work a full-time rotating shift schedule at one Ontario hospital were recruited for this study; 82 completed follow-up.

Primary and secondary outcome measures Study participants provided morning void urine and fasting blood samples for the assessment of aMTs-6 and sex hormone (oestradiol, oestrone, progesterone, prolactin) levels, respectively. These data were collected at two time points (summer and winter) such that relationships between melatonin and sex hormones could be assessed with respect to two time frames of interest (acute and cross-seasonal).

Results An inverse relationship between aMTs-6 and oestradiol was suggested in the winter (β=−0.18, p=0.04), but this result was not statistically significant in multivariate modelling that adjusted for age, body mass index and menstrual cycle. Likewise, while oestradiol, oestrone and progesterone levels increased with greater years of shift work history (all p<0.05), these associations were attenuated after confounder adjustment.

Conclusions These results do not support the proposed relationship between melatonin and sex hormone levels as biomarkers on the pathway of shift work and breast cancer but emphasise the importance of adjusting for confounders in modelling.

This is an open-access article distributed under the terms of the Creative Commons Attribution Non-commercial License, which permits use, distribution, and reproduction in any medium, provided the original work is properly cited, the use is non commercial and is otherwise in compliance with the license. See: http://creativecommons.org/licenses/by-nc/2.0/ and http://creativecommons.org/licenses/by-nc/2.0/legalcode.

https://doi.org/10.1136/bmjopen-2011-000532

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    Footnotes

    • To cite: Langley AR, Graham CH, Grundy AL, et al. A cross-sectional study of breast cancer biomarkers among shift working women. BMJ Open 2012;2:e000532. doi:10.1136/bmjopen-2011-000532

    • Funding This study was funded by the Workplace Safety and Insurance Board of Ontario and Breast Cancer Action Kingston.

    • Competing interests None.

    • Ethics approval Ethics approval was provided by Queen's University Research Ethics Board.

    • Contributors This manuscript presents results from an observational study (‘Occupational and other factors as determinants of melatonin levels among rotating shift nurses’) lead by Dr KJ Aronson (PI) and co-investigators Drs H Richardson, JE Tranmer, CH Graham, I Janssen and G Jones. The investigation of sex hormone levels among these nurses was completed as a substudy to the original work, lead by Dr KJ Aronson, AR Langley and A Grundy. ARL completed the statistical analyses, interpretation of results and manuscript writing with editorial support and intellectual input from all co-authors. All authors approved the final version of this manuscript.

    • Provenance and peer review Not commissioned; externally peer reviewed.

    • Data sharing statement There is no additional data available.