Institute of Cancer Epidemiology, Danish Cancer Society, 2100 Copenhagen, Denmark.
Eur J Cancer. 2012 Jul;48(11):1722-9. doi: 10.1016/j.ejca.2011.07.005. Epub 2011 Aug 16.
Working outside normal daytime hours is increasing worldwide and is now one of the most widespread potential carcinogenic occupational exposures. There is sufficient evidence in experimental animals that light exposure during the biologic night increases tumour growth and limited epidemiologic evidence that night shift-work cause breast cancer. Existing studies had crude definitions of shift-work and did not discriminate between shift-work systems (e.g. permanent versus rotating or evening versus night).
We performed an interview based nested case-control study within a nationwide cohort of Danish nurses, including detailed information on lifetime shift-work and potential confounders. Cases of primary breast cancer (n=310) were identified from the nationwide Danish Cancer Registry. Four control nurses were selected for each case by incidence density sampling. Odds rations (ORs) and 95% confidence intervals (CIs) were estimated by conditional logistic regression, with adjustment for potential confounders.
Overall, nurses who worked rotating shifts after midnight had a significantly increased OR (1.8; CI 1.2-2.8) for breast cancer compared to nurses with permanent day work. No association was found in a small group of nurses with evening work and no night work (OR=0.9; 0.4-1.9). The subgroup of nurses with periods of permanent night shift in addition to rotating night and day shifts experienced an OR of 2.9 (1.1-8.0). For nurses working after midnight compared to nurses never ending work before midnight, OR in the third tertile of cumulative number of shifts was 2.2 (1.5-3.2). In an analysis of different rotating shift systems, the highest OR (2.6; 1.8-3.8) was observed for long-term day-night rotating shifts.
The results provide further evidence that night shift-work may increase the risk for breast cancer and suggest that the largest impact on risk is associated with the most disruptive shifts.
Danish Cancer Society and National Programme of Environmental Health Research.
全球范围内，工作时间超出正常日间时间的情况日益增多，这现已成为最普遍的潜在致癌职业暴露因素之一。实验动物中有充分的证据表明，生物夜间的光照会增加肿瘤生长，且有限的流行病学证据表明，倒班工作会导致乳腺癌。现有研究对轮班工作的定义较为粗略，且未区分轮班工作制度（例如，永久性轮班与倒班轮班或上夜班与上晚班）。
我们在丹麦全国范围内的护士队列中开展了一项基于访谈的巢式病例对照研究，其中包括关于终生轮班工作和潜在混杂因素的详细信息。通过全国性丹麦癌症登记处确定原发性乳腺癌病例（n=310）。通过发病率密度抽样，为每个病例选择 4 名对照护士。通过条件逻辑回归估计比值比（OR）和 95%置信区间（CI），并调整潜在混杂因素。
总体而言，与从事永久性白班工作的护士相比，午夜后从事倒班工作的护士发生乳腺癌的 OR（1.8；95%CI 1.2-2.8）显著增加。对于很少一部分从事晚班工作且无夜班工作的护士，未发现相关性（OR=0.9；95%CI 0.4-1.9）。此外，除了倒班上夜班和白班之外，还有固定夜班的护士亚组，其 OR 为 2.9（95%CI 1.1-8.0）。与从不午夜前结束工作的护士相比，午夜后工作的护士，累计轮班次数处于第三 tertile 的 OR 为 2.2（95%CI 1.5-3.2）。在不同倒班系统的分析中，观察到最高的 OR（2.6；95%CI 1.8-3.8）是长期的日夜倒班轮班。
这些结果提供了进一步的证据，表明夜间轮班工作可能会增加乳腺癌的风险，并表明对风险的最大影响与最具破坏性的轮班有关。
丹麦癌症协会和国家环境健康研究计划。
