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Occup Environ Med 70:831-838 doi:10.1136/oemed-2013-101482
  • Workplace
  • Original article

Increased risk of breast cancer associated with long-term shift work in Canada

Editor's Choice
  1. Kristan J Aronson1
  1. 1Department of Public Health Sciences and Queen's Cancer Research Institute, Queen's University, Kingston, Ontario, Canada
  2. 2Department of Environmental and Occupational Health, School of Public Health, Drexel University, Philadelphia, Pennsylvania, USA
  3. 3Department of Cancer Control Research, British Columbia Cancer Agency, Vancouver, British Columbia, Canada
  4. 4Department of Pathology and Molecular Medicine, Queen's University, Kingston, Ontario, Canada
  5. 5School of Population and Public Health, University of British Columbia, Vancouver, British Columbia, Canada
  1. Correspondence to Dr Kristan J Aronson, Division of Cancer Care and Epidemiology, Queen's Cancer Research Institute, 10 Stuart Street, Kingston, Ontario, Canada K7L 3N6; aronson{at}queensu.ca
  • Received 5 March 2013
  • Revised 6 May 2013
  • Accepted 15 May 2013
  • Published Online First 1 July 2013

Abstract

Objectives Long-term night work has been suggested as a risk factor for breast cancer; however, additional studies with more comprehensive methods of exposure assessment to capture the diversity of shift patterns are needed. As well, few previous studies have considered the role of hormone receptor subtype.

Methods Relationships between night shift work and breast cancer were examined among 1134 breast cancer cases and 1179 controls, frequency-matched by age in Vancouver, British Columbia, and Kingston, Ontario. Self-reported lifetime occupational histories were assessed for night shift work, and hormone receptor status obtained from tumour pathology records.

Results With approximately one-third of cases and controls ever employed in night shift work, associations with duration demonstrated no relationship between either 0–14 or 15–29 years, while an association was apparent for ≥30 years (OR=2.21, 95% CI 1.14 to 4.31). This association with long-term night shift work is robust to alternative definitions of prolonged shift work, with similar results for both health and non-health care workers.

Conclusions Long-term night shift work in a diverse mix of occupations is associated with increased breast cancer risk and not limited to nurses, as in most previous studies.