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

Dr. Kristan Aronson and coworkers recently published a study on long-term night work and risk of breast cancer in the Journal of Occupational and Environmental Medicine. The case-control study found an increased risk of breast cancer in those who worked night shifts for at least 30 years. No association was found for shorter durations of night shift work.


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.


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