Exposure to flame retardant material may increase risk of thyroid disease

Research conducted at the University of South Carolina's School of Medicine suggests that exposure to low doses of a specific class of flame-retardant chemicals may alter the expression of thyroid hormones in the body, potentially leading to thyroid disease.

A study appearing in the journal Experimental Biology and Medicine found that low levels of polybrominated diphenyl ethers (PBDEs) appear to increase the amount of thyroid hormones in the bloodstream, a finding which seemingly contradicted prior research.

Previous investigation had indicated that PBDEs, albeit at higher doses, tend to decrease thyroid hormone production, leading to hypothyroidism.

Personal computers, televisions, carpets, furniture, mattresses and pillows may all contain PBDEs. Likewise, due to formerly extensive production of these chemicals in North America, they may be found in trace amounts in soil, water and air samples.

In the U.S., three commercial forms of PBDEs were once manufactured, which included penta-, octa-, and deca-BDE. Today, only deca-BDE is still produced in the country, the two other varieties having been phased out in 2004 due to changes in federal regulation.

In the new study, which was initiated to determine what effect lower levels of PBDEs have on the U.S. population, scientists injected pregnant laboratory rodents with a small dose of penta-BDE each day. Each animal typically received 60 micrograms of the chemical per kilogram of body weight.

The penta-BDE did not adversely affect the number of viable embryos produced by each rodent. However, researchers noted that the animals' DNA generally saw a three-fold increase in the expression of a gene controlling osteopontin, which is a protein that regulates a number of skeletal and immune functions.

Likewise, the laboratory animals displayed higher-than-average levels of thyroid hormones after low-dose exposure to penta-BDE. Furthermore, the offspring of these rodents tended to have enlarged thyroid glands, even though their levels of thyroid hormones were otherwise normal.

The group concluded that the long-term effects of maternal PBDE exposure may be biphasic, meaning low levels may lead to hyperthyroidism while higher levels could contribute to hypothyroidism.

In the U.S., pregnant women are at a slight risk for both thyroid diseases. Hyperthyroidism occurs in an estimated one in 500 pregnancies and hypothyroidism in up to three in 1,000 pregnancies, according to the National Institute of Diabetes and Digestive and Kidney Diseases.