British researchers found those who spend more than 11 hours a day — or 55 hours a week — at their desk faced a higher risk.
The most susceptible were women, younger people and those on a low pay grade with moderate alcohol consumption.
More than 2,000 Whitehall civil servants with various jobs, salaries and working hours were recruited in the 1990s for the study of employees aged 35 to 55. When they were followed up six years later, scientists at two London universities and colleagues in Finland found a ‘robust association' between overtime and depression — even allowing for other factors such as unhealthy lifestyles, marital status and job stress.
Of those questioned for the Whitehall II study, which is one of the most detailed on working hours and health in Britain, 66 had experienced a ‘major depressive episode' during the follow-up period, a rate of 3.1 per cent.
Those who worked 11 or more hours a day were two-and-a-half times as likely to have one than those who worked seven or eight.
The researchers said it seemed some who earned more could be ‘buffered' from depression by having a job they enjoyed, or by having staff who could do things for them.
Women in high-earning jobs were more likely to suffer depression, the researcher found, attributing it to multiple responsibilities outside work.