Social Isolation and Possible Implications for Breast Cancer

Martha K. McClintock, Ph.D.
Department of Comparative Human Development
University of Chicago
NIEHS Grant P50ES12382

A research report from NIEHS-supported scientists at the University of Chicago describes how social isolation early in life in laboratory rats is linked to a higher incidence of mammary tumors in mid-life. These findings could provide clues to the increasing incidence of breast cancer in humans.

Many human epidemiologic studies demonstrate significant associations between all-cause mortality and loneliness or social isolation. Other studies have shown that early puberty and delayed menopause are risk factors for breast cancer in women. The current research project focused on assessing the effects of isolation on patterns of ovarian development.

Four week old rats were housed either in groups of five or in single cages. The isolated rats developed regular ovarian cycles more quickly than the group-housed rats; however their cycles were shorter than the cycles of the group-housed rats. These differences resulted in more periovulatory surges of estrogen for the isolated rats and a "higher ratio of estrogenized to nonestrogenized days between 60 and 75 days of age when mammary tissue is receptor positive." However, mammary development was delayed in isolated females.

These results suggest that social isolation disassociates two components of puberty - it accelerated the maturation of the ovaries while delaying mammary tissue development. At 15 months of age, 100 percent of the isolated animals had tumors as compared to only 33 percent of the group-housed animals.

The researchers suggest that these findings may have implications for human well being. "Like animals, humans appear to have evolved capacities sensitive to the availability and reliability of social resources and adjust pubertal timing to environmental quality." They also suggest that their findings relate to the growing literature on the adverse health outcomes related to girls reaching puberty and experiencing breast development earlier in life than previous generations possibly leading to an increased risk of certain forms of breast cancer later in life. The research grant that supported this work is part of the NIEHS Centers for Population Health and Health Disparities Program.

Citation: Hermes GL, McClintock MK. Isolation and the timing of mammary gland development, gonadarche, and ovarian senescence: implications for mammary tumor burden. Dev Psychobiol. 2008 May;50(4):353-60.