A new US study found that socially isolated female rats developed more breast cancer tumors, including a higher number of malignant tumors, leading the researchers to suspect that the stress of isolation from a group triggered fear and anxiety which in turn increased susceptibility to and the deadliness of breast cancer. The results suggest there is a likelihood of a similar link in humans because like rats, we are a gregarious, social species.
The study is to be published in this week’s issue of the Proceedings of the National Academy of Sciences, and is the work of researchers at Yale University and the University of Chicago.
First author, Dr Gretchen Hermes, formerly a researcher at the University of Chicago, and now a resident in the Neurosciences Research Training Program in the Yale Department of Psychiatry, told the media that:
“There is a growing interest in relationships between the environment, emotion and disease. This study offers insight into how the social world gets under the skin.”
Led by senior author Dr Martha K McClintock, the David Lee Shillinglaw Distinguished Service Professor in Psychology and Comparative Human Development at the University of Chicago, the researchers monitored how mammary tumors developed spontaneously in rats living on their own and in groups.
Although spontaneous tumors occurred naturally in both groups, they found that the isolated rats developed significantly more tumors as the rats living in social groups. They also found that the tumors in the isolated rats were of a more malignant type.
The results showed that:
- Isolated rats who experienced the same stressors as rats linving in groups, such as being briefly constrained or sensing the smell of a predator, produced more of the stress hormone corticosterone.
- Isolated rats took longer to recover from a stressful episode than rats living in groups.
- While the stress hormone receptor entered the nucleus of mammary tumor cells (where gene regulation occurs) in both isolated and colony rats, it happend more often in the isolated rats.
- Isolated rats had a 135 per cent increase in the number of tumors and an 8,000 per cent increase in tumor size compared to colony rats.
- The effect of isolation was greater than other environmental factors, such as unlimited availability of high-energy food.
The researchers said the results suggested that living alone caused rats from a young age to have higher stress hormones, and experience higher levels of fear, anxiety and vigilance and this made them more prone to malignancy in late-middle age.
The researchers have shown in previous studies that fearful and anxious rats were more prone to tumors and death. And other studies have linked stress to various negative health outcomes, including the possibility that it may switch off the genes that suppress cancer.
Hermes proposed that the study showed a physiological link between loss of social networks and disease states that “may help explain the shortened life expectancy of individuals with mental illness”.
She suggested we need to look more closely at the health effects of isolation on a broad range of human diseases, and psychiatric disorders in particular.
“The costs of social neglect have unique relevance for psychiatric patients, the natural history of psychiatric illness and the profound co-morbidities associated with mental disease,” said Hermes.
McClintock agreed:
“We need to use these findings to identify potential targets for intervention to reduce cancer and other and its psychological and social risk factors.”
“In order to do that, we need to look at the problem from a variety of perspectives, including examining the sources of stress in neighborhoods as well as the biological aspects of cancer development,” she added.
“Social Isolation Dysregulates Endocrine and Behavioral Stress While Increasing Malignant Burden of Spontaneous Mammary Tumors.”
Gretchen Hermes et al
PNAS, (anticipated publication week beginning 6 Dec 2009).
Source: University of Chicago, Yale University.
Written by: Catharine Paddock, PhD