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

Long-term night shift work for ≥30 years is associated with a 2.21 times higher risk of breast cancer.

• Approximately one-third of both breast cancer cases and controls reported ever working night shifts.
• No significant relationship was found between night shift work and breast cancer for durations of 0-14 or 15-29 years.
• The association between long-term night shift work and breast cancer risk is consistent across various definitions of prolonged shift work.
• Increased breast cancer risk associated with long-term night shift work is observed in both health and non-health care workers.
• Findings suggest that the risk is not limited to specific occupations like nursing, which were the focus of earlier studies.

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