Abstract

In the epidemiological context, ‘exposure’ to shift work encompasses a variety of social, workplace, and individual characteristics. This complexity lends itself to coarse exposure assessment and assignment, which increases misclassification error and often reduces contrast between comparison groups. In early epidemiological studies of shift work, broad exposure assignment, such as ‘day’ versus ‘night’ worker, was commonly used; a technique that ignored various characteristics (e.g., shift intensity, timing, and work history) with potential impacts on long-term health risks.

In 2007, The International Agency for Research on Cancer classified ‘shift work that involves circadian disruption’ as a probable human carcinogen (Group 2A), on the basis of limited human evidence and sufficient evidence in experimental animals. In this evaluation, a major limitation of the epidemiological studies reviewed was the definition of shift work. A subsequent workshop convened by IARC considered how shift work should be assessed and quantified to improve the validity of future shift work and cancer studies. Since the publication of this working group’s recommendations in 2011, the role of strong exposure assessment as a vital component of informative epidemiological studies of shift work has increasingly been recognized.

As part of a proposed symposium on the importance of exposure assessment in epidemiology for hazard identification and risk characterization, this presentation will summarize progress to date in the adoption of stronger exposure assessment methodologies in epidemiological studies of shift work, and offer ideas for next steps. A particular focus will be placed on the refinement of measurement techniques to assess long-term exposure to shift work (e.g., roster-based assessment and validity studies), and on quantitative considerations of important co-exposures (e.g., light-at-night).