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Cancer Epidemiol Biomarkers Prev. 2020 Mar;29(3):687-689. doi: 10.1158/1055-9965.EPI-19-1314. Epub 2020 Jan 8.

Shift Work and Working at Night in Relation to Breast Cancer Incidence.

Author information

1
Epidemiology Branch, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina.
2
Department of Epidemiology, University of North Carolina, Chapel Hill, North Carolina.
3
Epidemiology Branch, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina. alexandra.white@nih.gov.

Abstract

BACKGROUND:

Night shift work has been classified by the International Agency for Research on Cancer as a probable carcinogen in humans. Several studies have assessed night shift work in relation to breast cancer risk, with inconsistent results.

METHODS:

In the prospective Sister Study cohort, current and past occupational history was collected for 48,451 participants. We used Cox proportional hazards models to estimate adjusted HRs and 95% confidence intervals (CI) for the association between baseline work schedule characteristics and incident breast cancer.

RESULTS:

During follow-up (mean = 9.1 years), 3,191 incident cases were diagnosed. We observed little to no increase in risk associated with work schedule characteristics (ever working rotating shifts: HR = 1.04, 95% CI, 0.91-1.20; ever working rotating night shifts: HR = 1.08, 95% CI, 0.92-1.27; ever working at night: HR = 1.01, 95% CI, 0.94-1.10; and ever working irregular hours: HR = 0.98, 95% CI, 0.91-1.06). Although short-term night work (>0 to 5 years vs. never: HR = 1.12; 95% CI, 1.00-1.26) and rotating shift work at night (>0 to 5 years vs. never: HR = 1.30; 95% CI, 1.05-1.61) were associated with increased breast cancer risk, working nights for more than 5 years was not associated with risk.

CONCLUSIONS:

Overall, we observed little evidence that rotating shift work or work at night was associated with a higher risk of breast cancer, except possibly among those who participated in such work for short durations of time.

IMPACT:

This study indicates that if night shift work is associated with breast cancer, the increase in risk is small.

PMID:
31915142
PMCID:
PMC7060110
[Available on 2020-09-01]
DOI:
10.1158/1055-9965.EPI-19-1314

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