The odds of a major depressive episode are more than double for those working 11 or more hours a day compared to those working seven to eight hours a day, according to a report is published in the Jan. 25 issue of the online journal PLoS ONE.

The authors, led by Marianna Virtanen of the Finnish Institute of Occupational Health and University College London, followed about 2000 middle aged British civil servants and found a robust association between overtime work and depression. This correlation was not affected when the analysis was adjusted for various possible confounders, including socio-demographics, lifestyle, and work-related factors.

There have been a number of previous studies on the subject, with varying results, but the researchers emphasize that it is hard to compare results across these studies because the cut-off for “overtime” work has not been standardized.

“Although occasionally working overtime may have benefits for the individual and society, it is important to recognize that working excessive hours is also associated with an increased risk of major depression”, says Dr Virtanen.