"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 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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Lesson 1: Never underestimate the effect of stress on your relationships at home.

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Drugs, food and habitual behaviors all have a direct effect on the biology of stress.

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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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Research on animals has suggested that stress can have an effect on tumour growth and the spread of cancer to other parts of the body.

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Dr Mrazek told BBC News Online that it was possible that the stress associated with parental problems caused chemical changes in the body that had an effect on the function of genes thought to be linked to the development of asthma.

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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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