Breast cancer and shift work
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Breast cancer and shift work



My presentation at Health and Wellbeing at Work conference, Birmingham.

My presentation at Health and Wellbeing at Work conference, Birmingham.



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  • Increasing incidence over timeUK has higher than average incidence (along with Belgium, Netherlands, France, Ireland)
  • Risk highest in over 70sEarly menarche, early first birth, breast feeding, and lower age of menopause all decrease riskHigher post menopausal levels of oestrogen and testosterone increase riskSmall increase from use of oral contraceptives, but the risk falls off in the ten years following stopping use^BMI ^ risk, ^activity v-riskAlcohol ^ risk and fat in diet ^ riskHeight^ risk – probably a marker for other risk factorsInterest in “light at night” and EMF exposure in relation to breast cancer in the 1980s

Breast cancer and shift work Breast cancer and shift work Presentation Transcript

  • WORKING FOR A HEALTHY FUTUREShift Work and Breast Cancer:What’s the evidence and what can we doto reduce the risks?John CherrieResearch DirectorINSTITUTE OF OCCUPATIONAL MEDICINE . Edinburgh . UK
  • Summary…• Breast cancer in the UK• Shift work involving night work• The epidemiological evidence relating to shift working• Intercontinental flights• Other data• The IARC evaluation• What can we do about this problem?• Other messages…
  • The statistics in the UK…• 49,564 women and 397 men were diagnosed with in breast cancer in 2010• 11,633 deaths from invasive breast cancer• 85% of women survive their invasive breast cancer for five years or more• The lifetime risk of developing breast cancer is estimated to be 1 in 8 for women
  • Risk factors…• Age• Reproductive factors, e.g. age at menarche, age at first birth, parity, breast feeding, age at menopause• Hormones, both endogenous and exogenous• Family history• Body weight and physical activity• Alcohol and diet• Height
  • Prevalence of shift work in the EU… Data for shift work involving night work From the IARC monograph
  • Tends in night shift work… EU15 data
  • The body of evidence for shift work…
  • Three studies published in 2001… Hansen J. Light at night, shiftwork, and breast cancer risk. J Natl Cancer Inst 2001;93:1513–5.
  • A recent systematic review… Risk of breast cancer for “ever” versus “never” night-shift workers Kamdar BB, et al. Night-shift work and risk of breast cancer: a systematic review and meta-analysis. Breast Cancer Res Treat 2013:1–11.
  • A recent systematic review…• Pooled relative risk: • ever night-shift work exposure 1.21 • short-term night-shift workers (<8 years) 1.13 • long- term night-shift workers (>8 years) 1.04• Review highlights flight attendants (with international or overnight work) and nurses working night-shifts long-term were at increased risk of breast cancer
  • Semiconductor workers in Scotland…• An initial cohort analysis showed a small non- significant excess of breast cancer • 20 deaths vs 15 expected• Detailed case-control study and further follow-up • Incidence of breast cancer still not significantly increased Hazard OR (95% CI) Nightshift 1.2 (0.4 – 3.5) Rotating shifts 1.9 (0.5 – 6.9) Circadian disruption 1.2 (0.4 – 3.5) Darnton A, et al. An updated investigation of cancer incidence and mortality at a Scottish semiconductor manufacturing facility with case-control and case-only studies of selected cancers. Occup Environ Med 2012;69:767–9.
  • Flight attendants… (A) Pukkala et al; (B) Haldorsen et al; (C) Rafnsson et al; (D) Reynolds et al; (E) Linnersjö et al; (F) Tokumaru et al. Tokumaru O, Haruki K, Bacal K, Katagiri T, Yamamoto T, Sakurai Y. Incidence of cancer among female flight attendants: A meta-analysis. Journal of Travel Medicine 2006;13:127–32.
  • Understanding the risks… Hansen J, Stevens RG. Case-control study of shift-work and breast cancer risk in Danish nurses: Impact of shift systems. Eur J Cancer. 2011 Aug. 16. 1–8.
  • Understanding the risks…
  • Alternative hypotheses…• Light at night suppresses the production of melatonin• Phase shift – animal studies have shown links between clock gene function and the induction of tumours• Sleep deprivation• Shift workers lifestyles that increase cancer risk,• Shift workers lay have lower vitamin D levels because of less exposure to daylight Fritschi, L. et al., 2011. Hypotheses for mechanisms linking shiftwork and cancer. Medical Hypotheses, 77(3), pp.430–436.
  • The IARC evaluation… Based on “limited evidence in humans for the carcinogenicity of shift-work that involves nightwork”, and “sufficient evidence in experimental animals for the carcinogenicity of light during the daily dark period (biological night)”, the Working Group concluded that “shift- work that involves circadian disruption is probably carcinogenic to humans” (Group 2A). Straif K, Baan R, Grosse Y, Secretan B. Carcinogenicity of shift-work, painting, and fire-fighting. Lancet Oncology 2007.
  • British cancer burden estimates… Men = blue Women = red 5.3% (4.6 – 6.6%) Rushton L, Bagga S, Bevan R, Brown TP, Cherrie JW, Holmes P, et al. Occupation and cancer in Britain. Br J Cancer 2010;102:1428–37.
  • British cancer burden estimates…
  • So what can we do?Ban women from night shifts? ✗Restrict the number of years women work nights ?Haverapidly rotating shifts (1–2 consecutive nights), which ✔causes less disruption of circadian rhythms?Use forward- rather than backward-rotating shifts? ✔Use bright lighting in the workplace? ✗Offer earlier or more intensive mammography screening to ✗female night shift workersMelatonin supplementation? ?Increase awareness and information for female workers ✔ Bonde JP, et al. Work at night and breast cancer – report on evidence-based options for preventive actions. Scand J Work, Env and Health 2012;38:380–90.
  • Any questions?