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Janet Gray, Ph.D.
Janet Gray, Ph.D.

As author of our 2008 and 2010 State of the Evidence reports, Dr. Gray drives the science behind all our work.

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Mycoestrogens (Fungal Estrogens)

CATEGORY*: Endocrine disruptor

FOUND IN: Contaminates animal feed, hay

THE GIST: Mycoestrogens are produced by fungi that contaminate cereal grains, animal feed sources, corn silage and hay. People are exposed to these compounds by eating grains contaminated with the fungi or by eating meat from animals that have consumed contaminated feed. Some of these estrogens have been linked to breast cancer, in addition to other kinds of cancer.

State of the Evidence on Mycoestrogens (Fungal Estrogens)

Like many plants, fungi also produce natural endocrine-disrupting compounds, including estrogenic mycotoxins. Fusarin C is a compound that contaminates cereal grains and has been linked to increased rates of esophageal cancer. It also stimulates growth and proliferation of MCF-7 breast cancer cells (Sondergaard, 2011). Zearalenone is another estrogenic mycotoxin produced by fungi that contaminates many animal feed sources, including corn silage and hay (Benxzoni, 2008; Mirocha, 1979).


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People are exposed to both compounds directly, by eating grains contaminated with the fungi, and indirectly, by eating meat from animals who have consumed contaminated feed.

The role of zearalenone on breast development and breast cancer in humans has received little attention in human studies. Zearalenone and its natural metabolites (breakdown products) were found in the blood of young girls with precocious puberty in a study in Italy (Massart, 2007). A more recent report from the Jersey Girl Study (Bandera, 2011) found that girls with higher urinary zearalenone levels, which came mainly from recent intake of beef or popcorn, tended to be less likely to have reached the onset of breast development and to be of shorter stature.

Zearalenone and its metabolites enhance proliferation of ER+ human breast tumor cells in vitro, through estrogen-mediated pathways and by activation of gene profiles similar to those activated by the natural hormone estradiol (Khosrokhavar, 2009; Parveen, 2009). Exposure of female rats to environmentally relevant doses of zearalenone during the last two (of three) weeks of fetal development and the first few days after birth resulted in long-term alterations in mammary gland development of the sort associated with increased risk for development of mammary tumors (Belli, 2010).

*For chemicals that have been shown to be carcinogens, we provide classifications from two authoritative bodies: the International Agency for Research on Cancer (IARC, an international body) and the National Toxicology Program (NTP, a division of the U.S. Department of Health and Human Services). We have categorized endocrine-disrupting compounds where the body of peer-reviewed research indicates a strong foundation for doing so.