Riassunto

Objectives Human evidence of carcinogenicity concerning shift work is inconsistent. In a previous study, we observed no elevated risk of total mortality in shift workers followed up until the end of 2006. The present study aimed to investigate cancer-specific mortality, relative to shift work.

Methods The cohort consisted of male production workers (14,038 shift work and 17,105 day work), employed at BASF Ludwigshafen for at least 1 year between 1995 and 2005. Vital status was followed from 2000 to 2009. Cause-specific mortality was obtained from death certificates. Exposure to shift work was measured both as a dichotomous and continuous variable. While lifetime job history was not available, job duration in the company was derived from personal data, which was then categorized at the quartiles. Cox proportional hazard model was used to adjust for potential confounders, in which job duration was treated as a time-dependent covariate.

Results Between 2000 and 2009, there were 513 and 549 deaths among rotating shift and day work employees, respectively. Risks of total and cancer-specific mortalities were marginally lower among shift workers when taking age at entry and job level into consideration and were statistically significantly lower when cigarette smoking, alcohol intake, job duration, and chronic disease prevalence at entry to follow-up were included as explanatory factors. With respect to mortality risks in relation to exposure duration, no increased risks were found in any of the exposure groups after full adjustment and there was no apparent trend suggesting an exposure–response relation with duration of shift work.

Conclusions The present analysis extends and confirms our previous finding of no excess risk of mortality associated with work in the shift system employed at BASF Ludwigshafen. More specifically, there is also no indication of an increased risk of mortality due to cancer.

Commento

Nel 2007 l'Agenzia Internazionale per la Ricerca sul Cancro (IARC) ha classificato tutte le tipologie di lavoro che comportano alterazioni croniche del ritmo circadiano come probabilmente cancerogene per l’uomo (gruppo 2A), fornendo spunti di ricerca per numerosi autori in letteratura che hanno recentemente analizzato, nei loro studi, l’impatto del lavoro a turni e notturno sul rischio di insorgenza di diverse tipologie di tumori compresi il cancro del seno, della prostata, della pelle e del sistema emopoietico. I risultati sul tema sono considerati suggestivi ma rimangono tuttavia, ad oggi, non ancora conclusivi.

Nella presente ricerca, in particolare, Yong e collaboratori hanno analizzato tutte le cause specifiche di mortalità in un corposo campione di lavoratori seguiti per un follow up di 9 anni, senza trovare aumenti statisticamente significativi né di mortalità specifica per cancro né di mortalità specifica per altre cause in associazione con il lavoro a turni e notturno.

Keywords

cancer risk, circadian disruption, Health surveillance, Industry-based cohort study, mortality, shift work

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