Social isolation and stress appear to increase susceptibility to breast cancer in rats, a US study has suggested.
Scientists at the University of Chicago found that rats which were prone to developing breast tumours were 3.3 times more likely to develop cancer if they were kept in isolation and suffered related stress.
In the study, which is published in the Proceedings of the National Academy of Sciences, researchers found that rats which were kept alone and subjected to stressful situations - such as the smell of a predator - tended to produce more of the stress hormone corticosterone.
These isolated rats took longer to recover from stressful situations than those which lived in small groups.
The researchers also discovered that rats which lived on their own typically had 135 per cent more tumours than those which lived in groups, and a more than 8,000 per cent increase in tumour size.
"We need to use these findings to identify potential targets for intervention to reduce cancer and ... its psychological and social risk factors," said Dr Martha McClintock, professor of psychology and comparative human development at the University of Chicago.
"In order to do that, we need to look at the problem from a variety of perspectives, including examining the sources of stress in neighbourhoods as well as the biological aspects of cancer development."
Ed Yong, Cancer Research UK's head of health information, noted that the study was only carried out in rats and that "overall, research in humans does not suggest there is a direct link between stress and breast cancer".
"But it's possible that stressful situations could indirectly affect the risk of cancer by making people more likely to take up unhealthy behaviours that increase their risk, such as overeating, heavy drinking, or smoking," he added.
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