Stress in the workplace is a major factor in the development of heart disease and diabetes, a study says.
Stress can have a damaging impact
Stress has long been linked to ill health, but the British Medical Journal study may have identified the biological process for the first time.
The study of 10,000 civil servants found a link between stress and metabolic syndrome, which involves obesity and high blood pressure.
Experts said the University College London report was "interesting".
Lead researcher Tarani Chandola said: "Employees with chronic work stress have more than double the odds of the syndrome than those without work stress, after other risk factors are taken into account.
"The study provides evidence for the biological plausibility of psycho-social stress mechanisms linking stressors from everyday life with heart disease."
During the study between 1985 and 1999, levels of work stress were measured four times.
The researchers also measured the different aspects of metabolic syndrome - a cluster of factors which cause heart disease and diabetes - such as high blood pressure and high cholesterol levels between 1997 and 1999.
Factors such as social class, smoking, high alcohol consumption and lack of exercise were all recorded as part of the study.
The researchers discovered that there was a link between the amount of stress experienced in their job and the levels of metabolic syndrome symptoms, even when considering the other risk factors.
This relationship meant that the more stress someone suffered, the more likely they were to suffer metabolic syndrome symptoms.
The researchers said that, for example, men who suffered chronic work stress were twice as likely to develop the syndrome as men who had no exposure to stress.
Women with chronic stress were also more likely to suffer from metabolic syndrome, although they formed only a small group in the study.
The researchers said one possible explanation for the result may be that prolonged exposure to work stress affects the nervous system.
They also suggested that chronic stress may reduce biological resilience, thus disturbing the body's physiological balance.
The study also found that both men and women from lower employment grades were more likely to have metabolic syndrome, confirming past reports that social status is linked to the risk of the syndrome.
A Diabetes UK spokesman said the study was "interesting" and confirmed what had long been suspected.
"The influence of work stress has been known to increase the likelihood of developing high blood pressure and heart disease which are factors for diabetes."
Professor Peter Weissberg, medical director of the British Heart Foundation, said stress was often linked to having little control over work.
And he added: "The good news is that many of the features of the metabolic syndrome can be reversed or improved by lifestyle changes, in particular increasing exercise and losing weight, combined with stopping smoking."