A new study on rats shows that isolation can accelerate the growth of breast cancer. That also means that staying connected with others can slow cancer growth.

Nothing is more stressful for human beings than loneliness and rejection from their social group. This is clearly the same for rats. When female rats are separated from their group shortly after birth, and brought up in isolation, they become particularly sensitive to stress. They also develop three times more breast cancers than females who live within a group, and their tumors are larger and more aggressive. [1]

Researcher Gretchen Hermes from Yale University attributes these results to the physiological effects of stress produced by loneliness. Rats who are isolated produce much more corticosterone, a stress hormone that is related to cortisol. Breast cells have receptors for this hormone, and Hermes is convinced that corticosterone can nourish cancer cells.

We know that in humans, loneliness is a major health risk; even greater than smoking. Isolation is probably a more important risk factor than what we ore generally refer to more generically as "stress.”

A few years ago, an Australian study showed that women who had experienced an episode of major stress did not have a higher than average risk of developing breast cancer in subsequent years. And women who had no close relationships - whether with a partner or with close friends -- were not at greater risk either. But women who had experienced major stress and who had no emotional support in their lives had a 9.5 higher risk of being diagnosed with breast cancer. [2]

In another US study that I've already quoted in this blog, nurses who had been treated for breast cancer had four times less risk of dying during the subsequent years if they could count on the support of at least one or two friends. Of note, in this study, whether or not they had a husband had no impact on their survival. Only friends -- usually girlfriends -- made a difference. [3] This new study on the impact of relationships among rats should remind us how important it is to resist helplessness and despair when we're facing illness. Our bodies actually seem to be able to protect us against many of the damaging effects of the stressful episodes that we inevitably encounter in our lives. But to help this happen, we need to learn how to ask for a little assistance from the people around us -- those who are most able to help us out. Above all, we need to avoid isolation and loneliness. When our hearts and bodies feel connected to others they can strengthen our ability to resist disease.


1. Hermes, G., et al., Social isolation dysregulates endocrine and behavioral stress while increasing malignant burden of spontaneous mammary tumors. Proc Natl Acad Sci U S A, 2009. 106 (52): p. 22393-22398

2. Price, M.A., et al., The role of psychosocial factors in the development of breast carcinoma: Part II. Life event stressors, social support, defense style, and emotional control and their interactions. Cancer, 2001. 91(4): p. 686-97.

3. Kroenke, C.H., et al., Social networks, social support, and survival after breast cancer diagnosis. Journal of Clinical Oncology, 2006. 24(7): p. 1105-11.