Long working hours increase diabetes risk in women: BMJ

According to the International Diabetes Federation, the most important challenge for prevention is now to identify social and environmental modifiable risk factors for the disease. Although previous research has pointed to a link between long working hours and heightened diabetes risk but most of these studies were done exclusively on men.

For the study, the researchers tracked the health of 7065 Canadian workers between the ages of 35 and 74 over a period of 12 years (2003-15), using national health survey data and medical records.

Participants' weekly working (paid and unpaid) hours were grouped into four-time bands: 15-34 hours; 35-40 hours; 41-44 hours; and 45 or more hours, and a range of potentially influential factors were considered. These included age; sex; marital status; parenthood; ethnicity; place of birth and of residence; any long-term health conditions; lifestyle; and weight (BMI).

Workplace factors, such as shift work, the number of weeks worked in the preceding 12 months, and whether the job was primarily active or sedentary, were also included in the analysis. During the monitoring period, one in 10 participants developed type 2 diabetes, with diagnoses more common among men, older age groups, and those who were obese.

• Long work hours did not increase the risk of developing diabetes among men.


• Among women, those usually working 45 hours or more per week had a significantly higher risk of diabetes than women working between 35 and 40 hours per week (HR: 1.63 (95% CI 1.04 to 2.57).


• The effect was slightly attenuated when adjusted for the potentially mediating factors which are smoking, leisure-time physical activity, alcohol consumption and body mass index.

This is an observational study, so no definitive causal effect can be established. What's more, working hours were measured at a one-time point only, and it wasn't possible to deduce from the medical records which type of diabetes participants had, although type I diabetes accounts for only around one in 20 adult cases.

Nor is there an obvious explanation for the gender differences the researchers found, although they suggest that women might work longer hours when all the household chores and family responsibilities are taken into account.

And long working hours might prompt a chronic stress response in the body, so increasing the risk of hormonal abnormalities and insulin resistance, they suggest.

"Working 45 hours or more per week was associated with an increased incidence of diabetes among women, but not men. Identifying modifiable risk factors such as long work hours is of major importance to improve prevention strategies and orient policymaking," concluded the authors.