Nurses” night-shifts doubles breast cancer risk
American Journal of Epidemiology (2017) 186 (5):532–540
Nurses who spend at least 20 years working night shifts are about twice as likely to develop breast cancer as those who never worked shifts, according to research from the USA. The risk is especially marked among nurses who worked shifts in their 20s and 30s.
Researchers used data collected during the Nurses” Health Studies. The Nurses” Health Study followed 78,516 women aged 42-67 years between 1988 and 2012. The Nurses” Health Study II followed 114,599 women aged 25-42 years between 1989 and 2013. During the 24 years follow up across both studies, the women developed 9541 invasive breast malignancies.
In the Nurses” Health Study, women with at least 30 years of shift work did not have a higher risk of developing breast cancer compared with those who never worked shifts. Follow-up, however, occurred mainly after the women had retired from shift work and the researchers assessed lifetime patterns of shift-work once near the end of the nurses” careers. Moreover, the nurses in this study were about 20 years older than those in the second trial.