People who work 11 or more hours a day are more than two times likely to go through major depression compared to those working seven to eight hours a day, a new study has warned. The researchers, 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," said Dr Virtanen. The study was recently published in the online journal PLoS ONE