PBDE Flame Retardant Linked to Thyroid Hormone Levels in Pregnant Women

• Endocrinology • • Pregnancy • Jun 21, 10

The largest study yet to investigate exposure to polybrominated diphenyl ether (PBDE) flame retardants and pregnant women’s thyroid hormone levels correlates exposure to PBDEs with reduced levels of thyroid-stimulating hormone (TSH) and increased odds of subclinical hyperthyroidism.

“There is very clear evidence from animal studies that PBDEs affect thyroid hormones, but very few human studies have attempted to determine whether pregnant women’s PBDE levels can impact the developing fetus,” says the study’s lead author, Jonathan Chevrier of the University of California, Berkeley, Center for Children’s Environmental Health Research.

“A mother’s thyroid hormones affect her developing baby throughout her pregnancy, and they are essential for fetal brain development,” says coauthor Brenda Eskenazi, director of the Center for Children’s Environmental Health Research.

PBDE flame retardants are found in a wide variety of U.S. consumer goods, including automobiles, airplanes, electronics, home furnishings, and furniture. Data collected by the U.S. Centers for Disease Control and Prevention (CDC) suggest PBDEs are found in the blood of almost all Americans.

Chevrier and his colleagues worked with a group of 270 women who were recruited in 1999 and 2000 to participate in the Center for Health Assessment of Mothers and Children of Salinas (CHAMACOS) study when they were pregnant. Most of the participants were Mexican American.

The research team used state-of-the-art methods to measure the women’s thyroid hormone levels, and they evaluated the data using models that adjusted for potential confounding factors, such as exposure to other persistent, bioaccumulative, and toxic compounds. Their analysis showed that women with higher blood PBDE levels had lower levels of TSH. The women with the highest levels of PBDEs were also more likely to have subclinical hyperthyroidism, defined as below normal levels of TSH with normal levels of the thyroid hormone thyroxine (T4).

Chevrier says the findings merit attention because of the crucial role that maternal thyroid hormone levels play in fetal development. The limited studies conducted to date are unclear on whether the low levels of TSH or the subclinical hyperthyroidism detected in the study affect fetal health.

“Women with low TSH may be above their natural set-point for the T4 thyroid hormone, which means that their thyroids may not be functioning normally,” Chevrier explains. “Elevated T4 in pregnancy has been associated with increased risks of miscarriage, premature birth, and intrauterine growth retardation,” adds Eskenazi.

In addition to Chevrier and Eskenazi, the paper’s authors include Kim G. Harley, Asa Bradman, Myriam Gharbi, and Andreas Sjödin. The study was supported by grants from the U.S. Environmental Protection Agency and the National Institute of Environmental Health Sciences. Additional funding was provided by the University of California Institute for Mexico and the United States (UC MEXUS).

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