Cohort study to investigate cancer incidence among shift workers at BASF

Status:

completed 09/2013

Aims:

In industrialized countries, about 15-20 % of the working population is involved in night working regimens. The International Agency for Research on Cancer (IARC) classified "shift-work that involves circadian disruption" as probably carcinogenic to humans in 2007 (IARC 2010). The rationale for this decision was summarized in by Straif et al. (Straif et al. 2007). While there is sufficient evidence for the carcinogenicity of chronodisruption from animal studies, the epidemiological evidence is limited. Epidemiological studies include large cohort studies of nurses and flight attendants, and the most evidence exists for breast cancer. Recent results suggest that chronodisruption may cause cancer in men, especially prostate cancer. However, the evidence is still limited. We conducted an epidemiological cohort study to investigate the incidence of cancer in male production staff employed at the BASF SE Ludwigshafen production site.

Activities/Methods:

Since several years, the Medical Service of the BASF intensively investigates the health of this cohort of 14 128 employees working in shifts and 17218 day workers. Since 1995, information on potential confounders such as age, smoking status, job level and job duration is available electronically. Cancer cases in the sub-cohort of employees living in Rhineland-Palatinate in the period 2000-2009 were determined by record linkage to the Cancer Registry of Rhineland-Palatinate. We compared the incidence of cancer in the cohort with that of the Rhineland-Palatinate population using standardized incidence ratios. We compared the cancer incidence risk in shift workers with that of day workers using Cox regression.

Results:

In the observation period, 518 and 555 incidental cases of cancer were observed (except non-melanoma skin tumors) under alternating shift workers and day workers, respectively, including 146 and 191 prostate cancer cases. The incidence of cancer in the total cohort des not greatly differ from that in of general population (SIR = 1.08 and 0.94). However, the incidence of prostate cancer was higher (SIR = 1.44 and 1.51) . Compared to day workers, shift workers had no increased risk of cancer overall (HR = 1.08; 95% CI: 0.93-1.26) or prostate cancer (HR = 0.96, 95% CI: 0.73-1.25) , but a non-significantly increased, risk of non-Hodgkin's lymphomas and leukemias, based on few cases. The results remain qualitatively the same when assuming different latency periods for cancer induction.

In this cohort, no increased risk for the incidence of cancer overall or prostate cancer for workers in rotating shift system was observed compared to day workers. In terms of cancer prevention in shift work, results from the present study suggest that no action is needed. Further research is needed to better determine the impact of individual chronotype, human metabolism and different shift work schedules on cancer risk.

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