According to a new study of people suffering from cancer, 'loneliness' can be deadly.
The research led by Yale University and the University of Chicago scientists, have shown that socially isolated female rats develop more tumors - and tumors of a more deadly type - than rats living in a social group.
"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," said Gretchen Hermes, first author of the paper and a resident in the Neurosciences Research Training Program in the Yale Department of Psychiatry.
They suspect that the real culprit is stress, triggered by being separated from a group.
Stress is linked to many negative health outcomes-including activation of cancer-promoting genes.
Lead researcher Martha K. McClintock at the University of Chicago, had previously shown that fearful and anxious rats were more prone to tumors and death.
The new study shows that social isolation and neglect can trigger the fear and anxiety, responsible for this susceptibility to cancer.
Although both the solitary and social animals developed tumors, the isolated rats developed 84 times the amount of tumors as those living in groups.
Those tumors also proved to be more malignant than those found in rats living in groups.
According to Hermes, health effects of isolation need to be studied more closely in a broad range of human disease, particularly psychiatric disorders.
"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," she said.
The expert added: "The results of this study make a physiological link between loss of the social network and disease states, and may help explain the shortened life expectancy of individuals with mental illness."
The findings appear in the Proceedings of the National Academy of Sciences.