Shiftwork in Canadian industries: A probable cancer risk factor

Status: completed


Our goal is to raise awareness of shiftwork as a probable cancer risk factor, and identify practical interventions that can be used in workplaces to reduce the negative health effects of shiftwork.


Night-time shiftwork has been classified as ‘probably carcinogenic to humans’ by the International Agency for Research on Cancer and was identified as a research priority by Occupational Cancer Research Centre stakeholders. Approximately 18.5% of the working population in Canada, or nearly 2.8 million workers, work a regular evening shift, regular graveyard shift, or a rotating (both days and nights) shift. Understanding which industries employ shiftworkers and the types of shifts that they work helps us to design research studies, predict health impacts, and target prevention efforts.


The Occupational Cancer Research Centre is undertaking a variety of activities related to shiftwork to assess knowledge and needs within the stakeholder community and create a venue for ongoing discussion and research.

The health effects of shiftwork

The first symposium, held in April 2010 in conjunction with the Institute for Work and Health, focused on the health effects of shiftwork. This meeting brought together the research, employer, labour, and workers’ compensation communities to discuss and evaluate the state of scientific evidence on shiftwork and human health. Presentations from international experts focused on the prevalence of shiftwork, biological mechanisms that may explain how shiftwork affects health, the results of animal studies, and the impact of shiftwork on worker injury, heart disease, fertility and cancer. All of the day’s presentations can be viewed here. The Occupational Cancer Research Centre has also prepared an Ontario Cancer Fact that summarizes the health effects of shiftwork and the major industries affected.

The classification of shiftwork as a carcinogen

The Occupational Cancer Research Centre held a “Classification of Carcinogens” workshop in February 2012 to outline the process that the International Agency for Research on Cancer (IARC) used to evaluate carcinogenicity, using shiftwork as the example. This workshop provided a background on the evidence of the health effects of shiftwork, including animal studies and epidemiologic studies, and showed why shiftwork was classified as a ‘probable’ carcinogen.

Interventions to reduce the health effects of shiftwork

Recognizing the need to extend this evaluation to interventions that reduce the potential risks of injury and disease among shiftworkers, the Occupational Cancer Research Centre and the Institute for Work and Health held a symposium on November 6, 2012, titled “Interventions mitigating health risks of shift work: Current knowledge and workplace practices”. In order to plan for this symposium, the OCRC and the Institute for Work and Health determined stakeholder needs and current knowledge via a web-based survey about workplace practices to prevent injury and illness due to shiftwork. The survey assessed knowledge of risk associated with shiftwork, identified types of interventions that have been proposed and/or implemented, determined who are the key players involved in shiftwork-related interventions, and collected information on what is needed to protect the health of shiftworkers. Survey respondents included workers, unions, employers, researchers, and policy-makers, among others. The survey results are now available. An Ontario Cancer Fact on interventions to reduce the health effects of shiftwork has been published, as well as a manuscript titled “Health-related interventions among night shift workers: a critical review of the literature.”

Results and other resources:

Future work includes investigating the link between shiftwork and cancer by using a database linking the 1991 Canadian census to the Canadian Cancer Registry.


Altogether, these efforts helped us develop a comprehensive picture of current knowledge and workplace practices for the prevention of injury and disease related to shiftwork. We have raised awareness of both the health effects of shiftwork and practical interventions among the stakeholder community.


Cam Mustard (Institute for Work and Health)
Kristan Aronson (Queen’s University)
Paul Demers (Occupational Cancer Research Centre and Cancer Care Ontario)
Desre Kramer (Occupational Cancer Research Centre)
Manisha Pahwa (Occupational Cancer Research Centre)
Anne Harris (Ryerson University)


Carolyn Gotay (Canadian Cancer Society-University of British Columbia Cancer Prevention Centre)
Sarah Neil (University of British Columbia)
Ron Saunders (Institute for Work and Health)