Shift work and health: What is the research telling us?

The Institute for Work & Health has scanned the research and called on experts to get the latest word on what we know – and don’t know – about the effects of shift work on employee health. There are certainly areas for concern, so more research on ways to protect shift workers is the logical next step.

Published: April 22, 2010

We live in a 24/7 world. From around-the-clock patient care in hospitals to overnight services in hotels and restaurants, there’s work to be done from sundown to sunrise. For more than a quarter of Canada’s employees, that means working shifts.

Shift work may be a social and economic necessity, but it is not necessarily a benign one. Research on the effects of shift work on health goes back for decades, says Dr. Ron Saunders, a senior scientist at the Institute for Work & Health (IWH). However, some research generated in the last few years – and the International Agency for Research on Cancer (IARC) finding that long-term shift work probably increases the risk of cancer – is really getting people’s attention.

This heightened attention spurred IWH and the Occupational Cancer Research Centre to co-host a symposium in mid-April on the possible health effects of shift work. The invitation-only event brought together experts from Canada, the United States and Europe to review the research evidence linking shift work to illness and injury (see box at right).

The symposium coincided with an upcoming Issue Briefing from IWH. Penned by Saunders, the briefing provides an overview of research findings on shift work as a cause of cancer, cardiovascular disease, gastrointestinal disorders, workplace injuries, sleep disorders and more.

Shift work tied to range of health effects

Shift work – essentially anything other than a regular daytime work schedule – is a reality for 26 per cent of full-time workers aged 19-64, according to Statistics Canada. About two-thirds of protective service workers (police officers, firefighters, security guards), 45 per cent of health workers, 40 per cent of sales and service workers, and 42 per cent of primary industry workers (farm workers, miners, forestry workers, etc.) are engaged in shift work.

As outlined in the Issue Briefing, the latest research points to the following about the health effects of shift work:

  • Long-term night shift workers probably have an elevated risk of breast cancer, and a potentially elevated risk of colorectal cancer. The IARC expert working group concluded that “shift work that involves circadian disruption is probably carcinogenic to humans.”
  • Elevated risks of gastrointestinal disorders, mental health problems (including depression) and preterm delivery during pregnancy are indicated among shift workers.
  • Shift workers, particularly those working nights, face a higher risk of getting hurt on the job than regular day workers. The risk is particularly high in the second hour of a night shift.
  • The association between shift work and heart disease is inconsistent. Although previous studies found a link between the two, a more recent systematic review found only limited evidence.
  • People who work night shifts are likely to sleep less and/or more poorly than regular day workers.

As for ways to reduce these health risks among shift workers, Saunders says the research on such strategies is scant. However, based on what is available, he says promising approaches include restricting the number of evening or night shifts in a row to three, limiting weekend work, moving from backward to forward shift rotations, and using a participatory approach to the design of shift schedules.

We need more research on ways to mitigate the harmful effects of shift work on health, says Saunders. That will require partnerships between workplaces and researchers in testing the potential benefits associated with different interventions.

To download the full Issue Briefing on shift work and health, go to: