Study nixes link between night shift work, breast cancer

  • Jones ME & al.
  • Br J Cancer
  • 29 May 2019

  • curated by Miriam Davis, PhD
  • Univadis Clinical Summaries
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Takeaway

  • A large cohort study finds that night shift work is unrelated to breast cancer onset.

Why this matters

  • This is among the largest and longest studies to date.
  • Findings may prompt the International Agency for Research on Cancer to revise its determination that night shift work is a probable carcinogen.

Study design

  • The UK Generations Study is a prospective cohort of women without breast cancer (n=102,869 recruited in 2003-2014) who were followed for up to 10 years.
  • Funding: Breast Cancer Now; The Institute of Cancer Research.

Key results

  • Median follow-up was 9.5 years.
  • No increased risk for breast cancer was seen with night shift work within the last 10 years (vs no night shift work; HR, 1.00; 95% CI, 0.86-1.15).
  • A significant trend was seen with average hours of night work per week (P=.035), but no increased risks were found for:
    • Hours worked per night.
    • Nights worked per week.
    • Average hours worked per week.
    • Cumulative years of employment.
    • Cumulative hours.
    • Time since cessation.
    • Type of occupation.
    • Age starting night shift work.
    • Age starting in relation to first pregnancy.
    • Receptor status of breast cancer (estrogen receptor-positive, progesterone receptor-positive, or human epidermal growth factor receptor 2-positive).

Limitations

  • Observational design.
  • Findings may not apply to other ethnicities.

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