Chemicals called phthalates and bisphenol-A (BPA) that are found in solvents, plastics and numerous household products may alter levels of thyroid hormones in the body, according to a new study.
Thyroid hormones play a role in many critical bodily functions, including reproduction and metabolism.
Researchers from the University of Michigan School of Public Health used data from the U.S. National Health and Nutrition Examination Survey to compare thyroid levels and traces of phthalates and BPA in urine samples of 1,346 adults and 329 teenagers. Their findings confirmed previous research linking BPA — used in certain plastic water bottles and the linings of canned foods — with disruptions in thyroid hormone levels, they said.
Overall, higher concentrations of the chemicals had an inverse impact on thyroid levels, said study lead author John Meeker, an assistant professor, in a university news release. The greater the exposure to phthalates and BPA, the lower the thyroid hormone levels.
The strongest link occurred with exposure to DEHP, a phthalate commonly used as a plasticizer, which people come into contact with through diet.
In the cases of DEHP ingestion, urine samples showed that the greatest exposure was associated with as much as a 10 percent drop in thyroid hormones.
"This seems like a subtle difference," said Meeker, "but if you think about the entire population being exposed at this level you'd see many more thyroid related effects in people."
The authors concluded that additional research is needed. In other ongoing studies, they are assessing the chemicals' potential effects on pregnancy outcomes and child development.
Developing fetuses and children may be particularly vulnerable to disruptions in thyroid hormone levels associated with exposure to these and other environmental chemicals, Meeker said.
The researchers, acknowledging some limitations of their study, said their work could be improved by following people over time and collecting several urine samples, since these chemicals metabolize quickly and one single sample may not represent the true chemical exposure.
The findings were published online July 11 in the journal Environmental Health Perspectives.