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. Thyroid hormones play a role in many critical bodily functions, including reproduction and metabolism.
Researchers 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.
It was found that overall, higher concentrations of the chemicals had an inverse impact on thyroid levels. 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. However, additional research is needed. In other ongoing studies, researchers 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.