The study titled "Adverse effect of long work hours on incident diabetes in 7065 Ontario workers followed for 12 years" was published in BMJ Diabetes Research & Care on July 2.

Previous studies on the link between diabetes and long working hours have largely focused on men. Epidemiologist Mahee Gilbert-Ouimet led the new study which examined data on 7,065 working adults in Canada who were tracked for a period of 12 years, from 2003 to 2015.

Based on the number of hours they worked each week, participants were divided into four groups: 15 to 34 hours, 35 to 40 hours, 41 to 44 hours, and 45 or more hours. 

At the end of the study, around 10 percent of the participants developed diabetes. Diagnoses were common among men, older adults, and those who were obese. However, when taking working hours into account, the incidence of the disease actually decreased among men who worked longer.

"I was surprised to see the somewhat protective effect of longer working hours among men," said Gilbert-Ouimet, a postdoctoral fellow at the Institute for Work and Health in Toronto. But this was not observed when looking at the female workers in the study.

Longer hours were associated with an increased incidence of diabetes among women. 45 hours was where the authors drew a line, finding that those who worked these many hours or more per week had a significantly higher risk (63 percent) compared to those who worked between 35 and 40 hours.

The authors suggested that working more than 40 hours a week could lead to stress i.e. changes in the production of hormones like cortisol. This can be linked to factors like sleep, insulin resistance, poor mental health etc.

However, the study was observational in nature so it was not yet established whether the long working hours themselves led to diabetes. The reasons for the gender difference, in particular, are not yet understood. One possible explanation, according to Gilbert-Ouimet, takes the division of family responsibilities into account.

"Among women, we know women tend to assume a lot of family chores and responsibilities outside the workplace, so one can assume that working long hours on top of that can have an adverse effect on health," she said.

The authors hoped that the study could highlight the importance of identifying modifiable risk factors like long working hours. Doing so could help "improve prevention and orient policy making, as it could prevent numerous cases of diabetes and diabetes-related chronic diseases," they concluded.