Rotating Night-Shift Work and Lung Cancer Risk Among Female Nurses in the United States

The risk of lung cancer among night-shift workers is unknown. Over 20 years of follow-up (19882008), we documented 1,455 incident lung cancers among 78,612 women in the Nurses Health Study. To examine the relationship between rotating night-shift work and lung cancer risk, we used multivariate Cox proportional hazard models adjusted for detailed smoking characteristics and other risk factors. We observed a 28 increased risk of lung cancer among women with 15 or more years spent working rotating night shifts (multivariate relative risk (RR) 1.28, 95 confidence interval (CI): 1.07, 1.53; P-trend 0.03) compared with women who did not work any night shifts. This association was strongest for small-cell lung carcinomas (multivariate RR 1.56, 95 CI: 0.99, 2.47; P-trend 0.03) and was not observed for adenocarcinomas of the lung (multivariate RR 0.91, 95 CI: 0.67, 1.24; P-trend 0.40). Further, the increased risk associated with 15 or more years of rotating night-shift work was limited to current smokers (RR 1.61, 95 CI: 1.21, 2.13; P-trend 0.001), with no association seen in nonsmokers (P-interaction 0.03). These results suggest that there are modestly increased risks of lung cancer associated with extended periods of night-shift work among smokers but not among nonsmokers. Though it is possible that this observation was residually confounded by smoking, our findings could also provide evidence of circadian disruption as a second hit in the etiology of smoking-related lung tumors.