Parabens like methylparaben (MP) and propylparaben (PP), which are commonly used in food, cosmetic, and drug preservatives, are associated with mammary cancer growth and metastasis in mice, according to a study recently published in Endocrinology.
Researchers led by Michele A. La Merrill, PhD, of the Department of Environmental Toxicology at the University of California at Davis, point out that the FDA considers methylparaben (MP) and propylparaben (PP) are parabens that are “generally recognized as safe” at 0.1% for each paraben in food. Humans are exposed to parabens through food and drugs, as well as through the skin via personal care products. “Consequently, parabens have been found in numerous human tissues, including adipose tissue, breast tissue, and tumors,” the authors write. “Recent nationally representative surveys of the US population detected MP in the urine of more than 99% of adults and children and PP in 95% of adults and children.”
The authors also note that there are disparities in exposures to parabens; non-Hispanic Black women and adolescents have disproportionately high levels of urinary MP and PP. “Given Black women are also more likely to die from breast cancer than white women in the United States, the possibility that their excess paraben exposure may cause increased breast cancer mortality merits examination,” the authors write.
These parabens bind with estrogen receptors (ERs) and stimulate mammary tumor cell growth and invasion in vitro, according to the authors. For this study, the researchers exposed female mice to MP or PP at levels the FDA considers “human acceptable daily intake.” The paraben-exposed mice had increased mammary tumor volume and increased pulmonary metastases compared to control mice. Further testing affirmed that MP and PP bound and activated human ER, and RNA-sequencing revealed increased ER expression in mammary tumors among paraben-exposed mice, the authors write.
“We show that paraben exposure at levels common in the US population are capable of accelerating mammary cancer growth and metastasis in mice through at least 2 key characteristics of carcinogens and alternative splicing events,” the authors write in their conclusion. “These data support the provocative possibility that disproportionate paraben exposure is related to the disproportionate risk of ER+/luminal breast cancer mortality among Black women.”
The authors go on to conclude that regulatory toxicology test guidelines for carcinogenicity are inadequately designed to replicate their findings. “The FDA should consider reevaluating the ‘human acceptable daily intake’ of these chemicals and consumers may wish to reexamine their personal care product use,” they write.