TUESDAY, July 2 (HealthDay News) — Prolonged night shift work (for 30 years or more) is associated with a significantly increased likelihood of breast cancer, according to a study published online July 1 in Occupational & Environmental Medicine.

Anne Grundy, from Queen’s University in Kingston, Canada, and colleagues examined the correlation between night shift work and breast cancer among a cohort involving 1,134 breast cancer cases and 1,179 age-matched controls.

The researchers found that about one-third of cases and controls were ever employed in night shift work. There was no association observed for 0 to 14 or 15 to 29 years of night shift work and breast cancer. There was evidence of a significant association for 30 or more years of night shift work and breast cancer (odds ratio, 2.21). This correlation was robust to various definitions of prolonged shift work. Similar results were seen for health and non-health care workers.

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“In summary, an association between ≥30 years of night shift work in diverse occupations and breast cancer is supported here, consistent with other studies among nurses,” the authors write. “As shift work is necessary for many occupations, understanding of which specific shift patterns increase breast cancer risk, and how night shift work influences the pathway to breast cancer is needed for the development of healthy workplace policy.”

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