Year: 2017
Type: article
Abstract: We reported little or no increase in breast cancer incidence associated with night shift work, either in three large UK prospective studies or in a meta-analysis that combined results from the three UK studies with those from seven previously published prospective studies (two in China, two in Sweden, one in the Netherlands, and the two Nurses’ Heath Studies in the United States) (1). Taking all the 10 studies together, the combined relative risks were 0.99 for any night shift work and 1.01 for 20 or more years of night shift work, compared with no night shift work. Restriction of our meta-analysis to findings from prospective studies, queried by Stevens and Hansen in their correspondences, is important when trying to detect or refute moderate hazards because it avoids the moderate biases that can result from retrospective methodology. Studies investigating human breast cancer risk associated with night shift work are not investigating directly the effects of changes in circadian rhythm, as Erren et al. point out in their correspondence. Our aim was specifically to examine the hypothesis that night shift work, and particularly long-term night-shift work, increased breast cancer risk. Since the publication of our findings in 2016 (1), follow-up has been extended to 3.5 years in the Million Women Study and to 4.1 years in EPIC-Oxford. The updated meta-analyses of findings from the 10 prospective studies now yield relative risks of 0.99 (95% confidence interval [CI] = 0.95 to 1.04) for any night shift work and 1.00 (95% CI = 0.92 to 1.09) for 20 or more years of night shift work, still consistent with little or no relation between night shift work and incident breast cancer. Meta-analysis of prospective evidence of breast cancer incidence associated with recent night shift work. Study-specific relative risks are represented by squares (95% confidence intervals as lines). Results were combined using inverse variance–weighted averages of log relative risks in each study, yielding a relative risk and its 95% confidence interval plotted as a diamond. Recent includes night shift work 10 or fewer years ago in the Million Women Study, EPIC-Oxford, and UK Biobank and in the past 1–5 years in the Danish study. In summary, the totality of the published worldwide evidence continues to show little or no increase in breast cancer risk associated with night shift work, including long-duration or recent night work.
DOI: 10.1093/jnci/djx008
Institution: University of Oxford
Language: English
Subfield: Experimental and Cognitive Psychology
Field: Psychology
Domain: Social Sciences
Open Access status: green
Funder: Cancer Research UK
Awards: G4221756634, G6723261869
OpenAlex ID: W4243407436