Diverse gut bacteria linked to reduced risk of breast cancer

30 October 2014

Postmenopausal women with diverse gut bacteria have a reduced risk of breast cancer through having a more favourable ratio of oestrogen metabolites, according to a study published in the Journal of Clinical Endocrinology & Metabolism (JCEM).

It has been known since the 1970's that the intestinal bacteria that make up the gut microbiome influence how women’s bodies process oestrogen, the primary female sex hormone. The bacteria determine whether oestrogen and the fragments left behind after the hormone is processed continue circulating through the body or are expelled through urine and faeces.

Previous studies have shown that levels of oestrogen and oestrogen metabolites circulating in the body are associated with risk of developing postmenopausal breast cancer.

“In women who had more diverse communities of gut bacteria, higher levels of oestrogen fragments were left after the body metabolized the hormone, compared to women with less diverse intestinal bacteria,” said one of the study’s authors, James Goedert, MD, of the National Institutes of Health’s National Cancer Institute (NCI) in Bethesda, MD. “This pattern suggests that these women may have a lower risk of developing breast cancer.”

“Our findings suggest a relationship between the diversity of the bacterial community in the gut, which theoretically can be altered with changes in diet or some medications, and future risk of developing breast cancer,” Goedert said. “Findings from this proof-of-principle study need to be replicated in larger groups of women. But we are hopeful that because the microbiome can change the way the body processes oestrogens, it may one day offer a target for breast cancer prevention.”

As part of the cross-sectional study, researchers analyzed faecal and urine samples from 60 postmenopausal women enrolled in Kaiser Permanente Colorado. The women were between the ages of 55 and 69, and all participants had a mammogram with normal results in the previous six to eight weeks. The samples were analyzed for bacterial diversity and the ratio of oestrogen fragments to oestrogen, a predictor of breast cancer risk.

Other participants in the study were from Kaiser Permanente Colorado in Denver, the Frederick National Laboratory for Cancer Research in Frederick, Maryland; and the University of Maryland in Baltimore, Maryland.


Associations of the Fecal Microbiome with Urinary Estrogens and Estrogen Metabolites in Postmenopausal Women. Journal of Clinical Endocrinology & Metabolism, published online, ahead of print.


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