A study published in the peer-reviewed journal Reproductive Toxicology shows low dose exposures to bisphenol A (BPA) to increase mammary epithelium in male mice (Vandenberg et al. 2013).

The researchers from Tufts University, USA administered BPA at doses of 0.25–250 μg/kg/day to pregnant and lactating mice and observed the effects in offspring. Male offspring showed changes in mammary gland morphology. More specifically, exposed males had visible epithelial ducts at all ages, when male mice usually have no nipples at all. The epithelium was found to be similar to female mammary epithelium and to have increased branching points and ductal area.

The findings suggest a link with breast enlargement in men, a common male breast disease called gynaecomastia. The doses administered in the study are comparable to exposures seen in humans. The dose-response relationship of the effects seen in the study was non-monotonic.

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Vandenberg, L. et al. (2013). The male mammary gland: a target for the xenoestrogen bisphenol A. Repro Tox (published online January 21, 2013).