Night Shift Work Increases the Risks of Multiple Primary Cancers in Women: A Systematic Review and Meta-analysis of 61 Articles

A growing number of studies have examined associations between night shift work and the risks of common cancers among women, with varying conclusions. We did a meta-analysis to identify whether long-term night shift work increased the risks of common cancers in women. We enrolled 61 articles involving 114,628 cases and 3,909,152 participants from Europe, North America, Asia, and Australia. Risk estimates were performed with a random-effect model or a fixed-effect model. Subgroup analyses and meta-regression analyses about breast cancer were conducted to explore possible sources of heterogeneity. In addition, we carried out a dose–response analysis to quantitatively estimate the accumulative effect of night shift work on the risk of breast cancer. A positive relationship was revealed between long-term night shift work and the risks of breast [OR = 1.316; 95% confidence interval (CI), 1.196–1.448], digestive system (OR = 1.177; 95% CI, 1.065–1.301), and skin cancer (OR = 1.408; 95% CI, 1.024–1.934). For every 5 years of night shift work, the risk of breast cancer in women was increased by 3.3% (OR = 1.033; 95% CI, 1.012–1.056). Concerning the group of nurses, long-term night shift work presented potential carcinogenic effect in breast cancer (OR = 1.577; 95% CI, 1.235–2.014), digestive system cancer (OR = 1.350; 95% CI, 1.030–1.770), and lung cancer (OR = 1.280; 95% CI, 1.070–1.531). This systematic review confirmed the positive association between night shift work and the risks of several common cancers in women. We identified that cancer risk of women increased with accumulating years of night shift work, which might help establish and implement effective measures to protect female night shifters. Cancer Epidemiol Biomarkers Prev; 27(1); 25–40. ©2018 AACR .