No link between night shifts and breast cancer, study concludes

Despite an assessment in 2007 that night shift work was probably carcinogenic, data from three new studies and a review of currently available evidence indicate that night shift work has little or no effect on breast cancer incidence. The work was led by Oxford University and is published in the Journal of the National Cancer Institute . In its 2007 review, the World Health Organization's International Agency for Research on Cancer categorised shift work that involves disruption of the circadian rhythm, people's internal 'body clock', as a probable carcinogen. This was based on evidence about breast cancer in animal studies. At the time, there was only limited evidence about breast cancer risk in humans. To examine whether night shift work could increase women's risk of developing breast cancer, Dr Ruth Travis and colleagues from the Cancer Epidemiology Unit at Oxford followed a total 800,000 women in three large UK studies and estimated the relative risks of breast cancer among women who reported night shift work versus no night shift work. Overall, 522,246 participants from the Million Women Study, 22,559 EPIC-Oxford participants, and 251,045 UK Biobank participants answered questions on shift work and were followed for incident cancer.