Wegrzyn LR, et al. – An inspection was pursued of the rotating night–shift work and the risk of breast cancer. A correlation was brought to light between the long–term rotating night–shift work with a higher risk of breast cancer, especially among women who performed shift work during young adulthood. The analysis of the role of shift work timing on breast cancer risk warranted advanced studies.

Methods

• The information was obtained from 2 prospective cohort studies, the Nurses' Health Study (1988-2012; n = 78,516) and Nurses' Health Study II (1989–2013; n = 114,559).
• This paper comprised of 9,541 incident invasive breast malignancies and 24 years of follow-up.

Results

• In the Nurses' Health Study, women with 30 years or more of shift work did not report a higher risk of breast cancer (hazard ratio (HR) = 0.95, 95% confidence interval (95% CI): 0.77, 1.17; P for trend = 0.63) compared with those who never did shift work, despite the occurrence of follow-up primarily after retirement from shift work.
• Among participants in the Nurses' Health Study II, who were younger than participants in the other cohort, the risk of breast cancer appeared to be considerably higher in women with 20 years or more of shift work at baseline.
• This, in turn, reflected young-adult exposure (HR = 2.15, 95% CI: 1.23, 3.73; P for trend = 0.23).
• It was found to be marginally, notably higher for women with 20 years or more of cumulative shift work when updated exposure information (HR = 1.40, 95% CI: 1.00, 1.97; P for trend = 0.74) was used.