Overtime 'linked to depression'

“Working eleven hours a day can lead to severe depression,” Metro has today reported. According to the newspaper, staff who put in 11 or more hours a day at the office are twice as likely to suffer a severe bout of depression than those working just eight.

This news is based on a study that examined the working habits of over 2,000 UK civil servants and how their working related to major depressive symptoms in the six years that followed. After accounting for other factors linked to depression, the researchers found that working 11 or more hours a week was associated with a 2.5 times increase the odds of experiencing a major depressive episode compared with their colleagues working the Civil Service’s standard seven to eight hours a day.

This research has found a link between working overtime and the risk of subsequent major depressive episodes. However, the relationship is complicated and this research cannot concretely tell whether or not overtime actually causes depression. Verifying this potential link would probably require controlled studies looking at whether or not cutting back work hours proves effective at reducing people’s risk of depression.

Also, this study found strong links between financial status, seniority and a reduced risk of major depression, making the influence of working hours harder to judge. Overall, it is likely that several factors work together to cause depression and the role working hours play in this is unclear.

The study was carried out by researchers from Queen Mary’s of the University of London, University College of London, the University of Bristol, McGill University in Canada, and the Finnish Institute of Occupational Health. The research was funded by the Medical Research Council, the British Heart Foundation, the Stroke Association and the US National Institutes of Health.

The study was published in the peer-reviewed scientific journal PLoS ONE.

The study was covered appropriately in the media, although headlines that suggested working overtime definitely causes depression are not supported by the research. The Daily Mail, The Daily Telegraph and The Independent all reported, in both their headlines and main story, that the research found an association or link between overtime and the risk of depression.

This was a prospective cohort study that examined the association between people’s number of hours worked a day and their risk of going on to experience a major depressive episode (MDE).

This research analysed data from a large well-known cohort study, called the Whitehall II study, which examined how work related to health in over 10,000 London based civil servants. This particular analysis on depression included full-time workers who were free from any psychiatric disorders and still employed at the time of the study’s follow-up period.

Prospective cohort studies have the advantage of ensuring that the exposure of interest (in this case, working hours) precedes the outcome of interest (experiencing MDE). This is one of several criteria needed to show causality. It is not, however, sufficient on its own to prove that the number of hours worked leads to or causes depression.

At the start of the study (known as the baseline) participants completed a survey that included questions on:

Participants were divided into four groups based on their working hours:

Approximately six years later they completed another interview that included a clinical health examination. At this interview, researchers determined whether or not participants had experienced a MDE during the previous year.

Researchers then analysed the data to assess how the odds of experiencing MDE in the two groups working the fewest and most hours. This analysis adjusted for possible confounding factors, including the baseline job characteristics, socio-demographic, health-related and physical health factors outlined above, in several separate analyses.

In all, 2,123 participants were included in the study. Those included in this study tended to be younger than those participating in the general Whitehall II cohort, and more likely to be male, married and from higher occupational grades. Participants were also more likely to experience low work strain than the Whitehall II cohort, and less likely to have a chronic disease or be a smoker.

Of the included participants:

Employees with the longest working days were more likely to be male, married, from higher occupational grades, have more active jobs and high social support at work compared to those who worked the standard seven to eight-hour day. In addition, they tended to drink more alcohol than the recommended daily limits and to be ex-smokers.

Of the 2,123 participants, 66 experienced a major depressive episode; this is equivalent to a 3.1% rate of depression. When assessing MDE risk, and adjusting for multiple potential confounding variables, the researchers found that employees who worked 11 to 12 hours a day had 2.52 time the odds of experiencing MDE compared to those who worked the standard seven to eight hours a day (Odds ratio [OR] 2.5, 95% confidence interval [CI] 1.12 to 5.65).

Other factors that were associated with increased odds of MDE were:

Factors that were not associated with increased odds of MDE included:

The researchers conclude that, ‘working overtime predicted the onset of a major depressive episode in a middle-aged cohort of British civil servants’. They add that this association held after adjusting for ‘a range of socio-demographic, lifestyle and work-related factors at baseline.’

This was a large cohort study that examined the association between the number of hours worked a day and the risk of subsequent major depressive disorder. It found that, after an adjusted analysis, those who worked three to four hours of overtime a day at the start of the study had a 2.5 fold increase in the chance they would go on to experience MDE.

The size and prospective nature of this cohort study mean that we can be quite confident in the results. There are, however, several limitations to the study that should be considered before insisting that our work hours are cut back. These include:

Overall, this research indicates that a very specific subset of civil servants were at increased risk of experiencing a major depressive episode. It is likely that several factors work together as ‘causes’ of depression and so the researchers were correct to avoid saying that they had found a cause.