Employees who work long hours with high job demands are more likely to develop depression, a study in the August Journal of Occupational and Environmental Medicine concludes.

Researchers analyzed job and workplace factors affecting depression risk in a group of 218 Japanese clerical workers. They found that employees who worked long hours (at least 60 per week) and had high job demands (defined as "usually" having too much work) were at higher risk of depression.

Workers who initially had the combination of long hours and overwork were 15 times more likely to have depression when re-evaluated one to three years later.

When adjusting for other factors, workers who went from long hours-overworked (LHO) status to non-LHO status were at a lower risk of depression, while those who moved from non-LHO to LHO were at an increased risk.

The risk of depression in LHO workers seemed to increase over time, according to the researchers.

"By targeting LHO, especially changes in LHO status, mental-health measures that effectively reduce the occurrence of major depressive disorder will become possible by controlling factors in the occupational environment," conclude lead researchers Takahashi Amagasa and Takeo Nakayama of the Kyoto University School of Public Health.

Previous studies have reported mixed results regarding the physical and mental health effects of long work hours. The new study highlights the importance of high job demands and feeling overworked – combined with long work hours – as a risk factor for depression in employees, the researchers assert.