Risk of work injury linked to night, evening shifts still high after switching to days

IWH study finds those who move into or out of shift work face the highest risks of work-related injury

Published: November 10, 2014

Tammy loves helping troubled youth, but working nights and weekends at a group home for youth had been hard on her family. The job meant missing out on homework time with her son, family outings on weekends, not to mention regular sleep. That’s why she can’t be happier to get a day job at the school board. She sees it as a chance to broaden her skills and improve well-being in her home life.

Trading in shift work for a nine-to-five job may mean a better quality of life for Tammy and her family. But it doesn’t necessarily mean a lower risk of work-related illness and injury, a recent study has found. Instead, Tammy’s risk of work-related injury may even increase shortly after she changes her work schedule into days, according to the study by Dr. Imelda Wong at the Institute for Work & Health (IWH).

Evidence shows that people working evening, night or rotating shifts face a higher risk of work-related injury than those who work days. But Wong’s study, published in the September issue of the Scandinavian Journal of Work, Environment & Health (doi:10.5271/sjweh.3454), now shows that the ones facing the highest risks are those who change from day jobs into shift work, as well as those who, like Tammy, change out of shift work into days. (Note that these refer to permanent or indefinite shift changes, not those linked to rotating shift work.)

This is surprising because we expected that moving into a daytime job may improve sleep and create a better work-life balance, thereby reducing the risk of work-related injury, says Wong, a Mustard post-doctoral fellow at IWH and lead author of the study. But we found that people who switch from nights to days are still two-and-a-half times as likely to get injured as those who have always worked days.

Six-year follow-up surveys

The researchers used Statistics Canada’s Survey of Labour and Income Dynamics, which examines the labour market activity of Canadians. A representative sample of Canadians is surveyed annually over six years, and with the permission of the respondents, income information is gathered from tax forms. The information contains such work-related details such as occupation, type of shift worked, weekly hours and number of workers in the establishment.

For this study, Wong used data from three survey periods spanning from 1999 to 2004, from 2002 to 2007, and from 2005 to 2010. Receipt of workers’ compensation or a work injury requiring more than seven days’ absence from work was used as the indicator of work-related injury.

Wong’s analysis looked at four categories of workers: those who only work days; those changing from days to non-standard shifts; those changing from shifts to days; and those working non-standard shifts the entire time. (People whose shifts changed routinely, as part of rotating-shift arrangements, were treated as non-standard shift workers.)

Results show that people who changed shift schedules and people who worked shifts shared many similar characteristics that are generally associated with greater injury risk (such as age, income, schooling level, etc.). But even after taking these factors into account, Wong found greater risks for a work-related injury linked to working shifts at any one point. Compared to day workers, long-term non-standard shift workers were 1.5 times more likely to be injured. However, the risks were even greater for those changing work schedules, whether to or from shift work. Those changing from day shifts into non-standard shifts were 2.6 times more likely to get hurt due to work; those changing into day shifts were 2.4 times more likely.

It’s still too early to say why the risk of sustaining work injury among shift workers remains high even after they change into daytime work. The data used in this study did not have any information that would help shed some light on that question.

It’s an interesting and concerning finding. At this time we can only speculate on what may be contributing to an elevated risk for those who switch from nights to days, says Wong. Still, I think this study tells us we need health and safety policies and programs for people who have made a change in shift schedules. It’s important to pay attention to health and injury risks even after someone has stopped working nights and moved into days.

Comparing risks between men and women

The study also looked at whether men and women face the same risks in non-standard shifts. It found women working long-term in non-standard shifts (i.e. nights, evenings and rotating shifts) face a significantly higher risk of work-related injury than men.

We don’t know if this is due to differences between men and women in terms of health, work conditions, job duties, home-life responsibilities such as caregiving, household chores, or other factors, says Wong. We certainly need more research to find out what might be behind these sex and gender differences.

These findings suggest the need for greater safety measures to protect shift workers, in line with the International Labour Office (ILO)’s Night Work Convention, says Jon Messenger, a team leader at the ILO’s Conditions of Work and Equality Department.

As well, he adds, the findings suggest “the need for these measures to be gender-sensitive, given that these greater risks could be due to gender-related factors such as women’s greater total work burden arising from unpaid household work.”