The list of health problems that scientists can confidently link to exposure to hormone-disrupting chemicals has grown to include diabetes, cardiovascular disease, and obesity, a new scientific statement suggests. The statement, released today by the Endocrine Society, also adds support to the somewhat controversial idea that even minute doses of these chemicals can interfere with the activity of natural hormones, which play a major role in regulating physiology and behavior.
But the report—which updates a similar statement released in 2009—is drawing sharp criticism from the chemical industry.
An executive summary of the new statement, which synthesizes 1300 studies on endocrine disrupters, posits that scientists are more confident than ever before in linking these substances to a host of known health issues, including reproductive and developmental problems, thyroid impairment, certain reproductive cancers, and neurodevelopmental problems such as decreased IQ. But studies suggest those links can now be extended to heart and weight problems, and diabetes, says the executive summary's first author, Andrea C. Gore, a professor of pharmacology and toxicology at the University of Texas, Austin. Six years ago, scientists couldn’t make such a strong case for those links, Gore says, because there weren’t enough good studies. “But this has really been an emerging field where there is much stronger evidence now,” Gore told reporters today on a conference call.
Still, some toxicologists and industry groups have long disputed the assertion that endocrine disrupters can trigger effects at minimal doses; this idea can be tough to test in lab animals, which are usually exposed to high doses in toxicology studies. And critics of the new report say it doesn’t appear to clarify the 2009 version’s vagueness about what it means for an endocrine disruptor to cause an "adverse effect."
The summary of the new report "makes broad, unsupported claims about the relationship between certain chemicals and disease," the American Chemistry Council, the largest trade group for the chemicals industry, argued in a statement. Regulatory agencies such as the Environmental Protection Agency (EPA) still haven’t embraced the idea that minute doses of endocrine disrupters can cause health problems, the Washington, D.C.–based industry group adds. And the Endocrine Society has failed to clarify when a chemical causes a scientifically proven “adverse effect,” the council argues (versus merely displaying endocrine activity).
The National Research Council has launched a multiyear review of whether EPA’s current chemical assessment practices properly capture low-dose endocrine-related effects. In the meantime, Gore rejects the criticism that the Endocrine Society has not adequately defined “adverse effects.” She notes that in studies on lab animals, some toxicologists mistakenly assume that endocrine disrupter–related health problems must show up right away. But such health problems can take years or even decades to manifest in humans, she says, and months in lab animals. And the specific disease that the chemicals may induce in the animals often isn’t always known from the study’s outset, she adds. "I think the issue has been resolved for endocrinologists and for many toxicologists," she says.
The Endocrine Society executive summary strongly emphasizes studies involving bisphenol A (BPA), phthalates, persistent organic pollutants such as polychlorinated biphenyl ethers, and flame retardants such as polybrominated diphenyl ethers. "These chemicals had the greatest depth and breadth of available information," the executive summary says.
But the summary adds that most industrial chemicals released into the environment—numbering in the tens of thousands—have never been tested for endocrine-disrupting potential. Moreover, Gore added, scientists are increasingly finding that some chemical replacements for BPA and other suspected endocrine disrupters display endocrine-disrupting potential themselves. These conclusions, the summary says, highlight the need to test chemicals before they enter commerce and to better educate the public and policymakers on how to prevent exposures.
Emerging testing methods, such as high-throughput screening assays, could help researchers identify which of the thousands of chemicals in the environment now need the most scientific scrutiny, the summary suggests. (EPA is currently exploring the use of these methods to prioritize which chemicals merit full-fledged animal testing for endocrine-disrupting effects.)
The Endocrine Society also calls for more endocrine research funding in general, arguing that the benefits to society will far outstrip the costs. Funding agencies should emphasize "team science" projects, not simply individual studies by individual scientists, the summary argues.
The society recommends several areas for expanding research. Researchers should increase the range of studied hormone receptors—proteins that receive chemical signals from hormones—to see how endocrine disrupters might affect them. And future research could increasingly target sex-specific responses and the effects of mixtures of multiple endocrine disrupters, the summary says.