A novel data analysis was used to show a non-monotonic dose relationship between exposure to bisphenol A (BPA) and mammary gland development. The study, which was part of the Consortium Linking Academic and Regulatory Insights on BPA Toxicity (CLARITY-BPA) project, was conducted by researchers from Tufts University and National Toxicology Program (NTP) laboratory. Results of the study, titled “A Combined Morphometric and Statistical Approach to Assess Non-monotonicity in the Developing Mammary Gland of Rats in the CLARITY-BPA Study,” were published May 20, 2020, in the peer-reviewed journal Environmental Health Perspectives.

A questions and answers document (Q&A) on the study, developed by the Health and Environmental Alliance (HEAL), explains that the researchers used both traditional semi-quantitative methods and a novel quantitative method, which was “developed specifically in the context of this study in order to precisely access the dose response curves,” to evaluate the data. The Q&A further points out that this statistical method “makes it possible to provide a rigorous analysis of the non-monotonic does response curve.” Unlike monotonic dose responses where the response increases as the does increases, with non-monotonic dose responses (NMDR) the slope of the curve relating dose and effect changes direction at some point within the range of the doses examined.

The analysis of 91 measurements from rats exposed to BPA showed a non-monotonic dose-response curve on mammary gland development at all ages examined, with a break between the 25ug/kg/day and 250 ug/kg/day doses. The researchers concluded that this study shows that lower doses result in larger effects. A final report integrating published findings from the CLARITY Core Study and Grantee Studies, including this study, will be prepared. This report will contain chapters organized around the organ systems studied by the grantees, integrating information by dose, time, and endpoint from the two components of the CLARITY-BPA program.