"We did not find strong evidence that the effect of work stress on heart disease is worse for those in lower grades - the effect of stress was pretty much the same across different grades, " said Dr Chandola.

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The study, which looked at nearly 600 sets of Swedish twins, some identical, some fraternal, who were either raised together or separated early and reared apart, found that being raised in the same environment had little effect on stress and stress-related health problems.

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"It's a source of marriage breakdown, of stress, of people being ill, being off work - the knock-on effect of people wrestling with unmanageable debt in their lives can be massive, " he says.

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The scientists could see that this activity had the effect of reducing stress levels, indicated by the return to the animals' normal activities of self-scratching and self-grooming.

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