Regular overtime increases risk of depression, study finds

Feb 6, 2012, 3:06 GMT

London - Working three to four hours overtime daily over an extended period increases the risk of major depression, according to a British study. The findings appeared in the journal PLos ONE, published by the Public Library of Science (PLoS), a non-profit organization with headquarters in San Francisco.

Led by Marianna Virtanen from University College London and the Helsinki-based Finnish Institute of Occupational Health, the study followed 2,123 civil servants in Britain - 1,626 men and 497 women with an average age of 47 - for periods ranging from 3.8 to 7.2 years. All were considered mentally healthy at the start of the study, and 11 per cent averaged workdays of 11 hours or more.

Sixty-six of the subjects, or 3.1 per cent, developed major depression. Thirty-eight of them were among the 1,105 subjects who worked a standard seven- to eight-hour day, and 10 were among the 227 with 11- to 12-hour workdays. Other possible factors for their depression were taken into account. The conclusion: People who work a lot of overtime are twice as likely to suffer from major depression than those who do not work overtime.

'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,' Virtanen said.

The researchers conceded that 'plausible explanations' of why long working hours were linked to an increased incidence of depression could not be drawn directly from their study. But other studies, they said, have given indications that too much time on the job could lead to family conflicts, difficulty unwinding after work and more stress hormones in the blood.

Data used by the researchers come from a study known as Whitehall II, which started in London in 1985 and includes more than 10,000 British civil servants. The subjects are considered to be generally healthier than the national average. The researchers noted, for example, that the civil servants' rate of major depression -- 3.1 per cent -- was lower than the approximately 5 per cent found in studies of Britain's general populace.

Virtanen and her fellow researchers said that further studies, targeting blue-collar or private sector workers, were therefore necessary. They also said that some studies on overtime had reached different results on depression rates. There is often no clear definition of when overtime begins, they said.

In 2010, the authors of the study published a paper saying that overtime could be harmful to the heart. Data from about 6,000 civil servants in London showed that three to four hours of overtime daily increased the risk of coronary heart disease by 60 per cent, they said.