On a "lucky" day at her job at a well-known apparel company, Arielle Smith worked a 10-hour shift with only 20 minutes for lunch -- and many weekends, she worked without overtime pay. "I never slept because I was so stressed about what would happen the next day," said the 27-year-old fashion designer from New York City. "I wasn't supposed to leave the office at all, except to run work errands. I thought about switching jobs every single day." Her workload eventually took its toll: She was medicated for anxiety and depression. Work can be depressing, that much most people know. But now, a European study suggests that those who work long hours are twice as likely to experience a major depressive episode. In a report published in the Jan. 25 online journal Plos ONE, those working more than 11 hours a day are at greatest risk. Researchers at the Finnish Institute of Occupational Health and at University College in London followed 2,000 middle-aged government workers in Britain and saw a link between overtime work and depression. The study was adjusted for other variables, such as socioeconomic backgrounds, lifestyle and other work-related factors. Another study of the same group last year found that a 67 percent higher risk of coronary heart disease study authors conceded results might have been different had they studied a younger age group. "It is true that depression is more common in middle age, and it might also be possible that in order to have any effect on health, quite a long period of exposure to long hours is needed," said Marianna Virtanen in an email to ABCNews.com. The average number of hours worked annually by employees in the United States has steadily increased, according to the Centers for Disease Control (CDC) and Prevention's 2004 report, "Overtime and Extended Work Shifts." American workers now surpass Japan and most of Western Europe in numbers of hours devoted to the job, the CDC reported. Bruce, a 33-year-old lawyer from New Jersey who did not want to be identified further, copes with the pressures of working so many hours and sometimes worries about his own mental health. He typically works 10 hours a day and often works nights and weekends. "Everyone is working harder in this economy," he said. "The work is always there. I am always on call. I am certainly not alone." He said the study "makes a lot of sense." "I have seen it in my own practice as well as watching colleagues deal with those issues," said Bruce, who has a family. "I think it's the pressure of being on all the time and balancing that against all the other obligations in life." According to the CDC's National Institute for Occupational Safety and Health, psychological illnesses are an area of increasing concern to organizations, because depressive disorders are among the most costly for companies and contribute to productivity losses. The precise cause of depression is unknown. Often, combinations of genetic, cognitive and environmental factors are associated with its onset, according to the National Institute of Mental Health. Trauma, as well as "stressful change in life patterns" can be to blame. For more than 15 years, psychiatrist Dr. David Reiss has evaluated 10,000 "stress claims" through the California Worker's Compensation Program. Today, he serves as medical director at Providence Hospital in Holyoke, Mass. "The real issue is people are overworked and they get mad during projects and have conflicts with their co-workers or supervisors and it gets out of hand," said Reiss. "It can be anything from burning out to feeling they are not spending enough time with their family." "Their sleep patterns are disrupted, they aren't exercising," he said. "For people who work long hours, it takes a toll. Some are invulnerable, but most are not." Reiss has seen a decreasing number of claims because people are afraid of losing their jobs. "They are tolerating more," he said. "But once they hit bottom, it is worse." That happened to Shari McGuire of Maple Grove, Minn., who became clinically depressed after averaging 70 hours a week working for a large corporation. "The pressure was unbelievable," she said. "It was an enormous feat to get things done by so many deadlines." In 2007, her son was born. "I wanted to be home with my baby, and I didn't know how to grow my career without the extra hours," said McGuire, now 43. She sought help, but she said the antidepressants made her feel like there was "an even bigger cloud over my head." "One depression medication wasn't enough, so a second medication was added," said McGuire. "I knew that there had to be a better way to make a living because I was missing out on so much life." When she noticed that she was visibly absent from photos with her now-5-year-old son, she knew it was time to reevaluate her 19-year career and walked away from her "six-figure job." The last straw was in 2010, when she was expected to explain a $20,000 gap in the budget on a conference call. "I had worked 70 hours that week and I could have spent 80 hours," she said. "I realized, 'I can't do it anymore,' and quit." After an unsuccessful attempt to start her own business, she took another information technology job. But this time, she set limits. Now, she has been off medication for a year. McGuire wrote about her experience to help others in a book, "Take Back Your Time: 101 Simple Tips to Shrink Your Work-Week and Conquer the Chaos in Your Life." The key, she said, is not managing time better, but "changing your behavior." "I now only work 40 hours a week and I am happier," she said. "I can live my life again. ... If your job doesn't allow you to do that, you are in the wrong job."