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Work stress is making people from doctors to plumbers mentally ill, new research has found.

The Dunedin-based study found that 14 per cent of women and 10 per cent of men who were stressed at work suffered depression or anxiety when aged 32. They had not had these conditions before.

They were among nearly 900 people Otago University has been following since they were born in 1972-73.

For the latest paper, they were asked at the age of 32 about psychological and physical job demands, the level of control they had in decision-making and social support structures at work.

The paper, published in the British journal Psychological Medicine, found that women who reported high levels of psychological job demands - such as long hours, pressure or lack of clear direction - were 75 per cent more likely to suffer from clinical depression or general anxiety disorder than women who reported the lowest levels.

Men with high levels of these work stress factors were 80 per cent more likely to be depressed or anxious than those with the lowest levels.

Separate research has found that 16 per cent of New Zealanders suffer major depression and 6 per cent have general anxiety disorder at some point in their lives.

The director of the long-term Dunedin study, Professor Richie Poulton, said previous research had suggested a connection between work stress and depression and anxiety. However, this study was the first to establish the association independently of other factors in mental disorders, such as personality type and socioeconomic status.

But the study did not find any differences between jobs.

"The most toxic factor here is high psychological demands," he said. "That can be present in multiple professions: the media are always working under time pressure; doctors, firemen, nurses, builders, plumbers ... it applies across the board."

He said the latest study, a collaboration with King's College, London, was done because rates of depression, anxiety disorders and people's stress levels had increased.

Because of the costs of mental disorders he urged employers to minimise stress for their workers.

Business NZ chief executive Phil O'Reilly said smart employers were already doing that.

"A key to minimising workplace stress," he said, "is excellent communication between employers and employees, to minimise confusion, to make sure people are clear about what they are doing."

Job stress costs

* 45 per cent of newly diagnosed cases of depression or generalised anxiety disorder were directly related to workplace stress.

* 12 per cent of people who experienced stress at work and had no history of mental health problems had a first episode of depression or anxiety at the age of 32.

* People with high levels of psychological demands at work were 75-80 per cent more likely to suffer from depression or anxiety than those with the lowest levels.

Source: Otago University study of 891 people aged 32.