OHS Canada Magazine

Study: workers who switch shifts have high injury risk

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November 17, 2014
By Jeff Cottrill

Health & Safety shift work

Workers who switch shifts more likely to be injured than permanent night-shift workers

(Canadian OH&S News) — A longitudinal study by Toronto’s Institute for Work & Health (IWH) has concluded that not only do evening-shift and nightshift workers have a higher injury risk than that of daytime workers, but workers are even more at risk when they switch between shift schedules.

“For better or worse? Changing shift schedules and the risk of work injury among men and women”, published in the September issue of the Scandinavian Journal of Work, Environment & Health and recently summarized in the fall issue of IWH newsletter At Work, used data from Statistics Canada’s Survey of Labour and Income Dynamics. This survey examines occupation-related information from samples of Canadian workers over six-year periods.

Study author and IWH post-doctoral fellow Dr. Imelda Wong reviewed three of the survey periods – 1999-2004, 2002-2007 and 2005-2010 – and noted injuries leading to either more than a week’s absence from work or receipt of workers’ compensation. She also classified workers into four categories: those who worked days only; those who worked only “nonstandard” shifts, i.e. evenings or nights; those who switched from daytime hours to nonstandard shifts; and vice-versa.

“We had hypothesized that people who worked regular daytime shifts would have a more protective environment or might have better sleep habits,” said Dr. Wong, who is a director of the Shiftwork and Working Time Society of the International Commission on Occupational Health, “and so switching from a nonstandard shift to a regular daytime shift may actually reduce the risk of injury.”

The study found that people who worked nonstandard shifts permanently were 1.5 times more likely to be injured than were those who worked day hours permanently – but that number rose when dealing with workers who changed shifts. People who changed from nonstandard hours to daytime hours were 2.4 times more at risk of injury than permanent nine-to-five workers were, and those who switched from day to nonstandard were 2.6 times more at risk.


Dr. Wong said that nothing in the data explained why workers who switched shifts were more at risk. She theorized that health conditions and disrupted cognitive functions might have been contributing factors. “It could be a variety of different things,” she said. “It just opens up a lot of opportunities for future studies to explore this even further.”

The same study also compared the injury rates between men and women, finding that women who worked nonstandard shifts on a permanent basis were at a higher risk of occupational injury than were men on nonstandard shifts. But the risk of injury for those who switched shifts, while still higher, was similar for both genders.

Dr. Wong was limited to speculation when explaining the difference between genders for injury risk in nonstandard shifts. “It could be linked to work-life-balance issues. There, studies have shown that women generally spend more time on household duties, like healthcare, than men,” she noted. “Men and women tend to work in different occupations, so they might have different exposures to different hazardous conditions.” She suggested compensation as another possible factor. “Some studies have shown that women and men have different experiences with the compensation system.”

“For better or worse?” is an extension of a study that Dr. Wong conducted in 2011, when she explored the difference in injury risks between men and women who worked different shifts permanently.

“I’m hoping this paper generates more discussion among employers and employees and policy makers about the risks associated with shift work,” she said. “The results may highlight the need for more occupational health and safety policies and programs.”

The 11-page study is available for download at http://www.sjweh.fi/show_abstract.php?abstract_id=3454.


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