Strong evidence from a new study in human placenta suggests that Endocrine Disrupting Chemicals (EDCs) can interfere with the action of thyroid hormones in pregnant women. The study has found that flame retardant chemicals called polychlorinated biphenyls (PCBs) can infiltrate the placenta during pregnancy and affect thyroid hormone activity at the cellular level, according to a study published in the Endocrine Society’s Journal of Clinical Endocrinology & Metabolism (JCEM).

In the past, PCBs were used in transformers and other electrical equipment, paints, adhesives, and tape. Although the endocrine-disrupting chemicals were banned in the U.S. in 1979, PCBs still are released into the environment from disposal sites or products manufactured prior to the ban. Most people have been exposed to low levels of PCBs. Scientific findings suggest these endocrine disrupting chemicals interfere with the thyroid hormone, which is essential for brain development in fetuses and newborns.

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The prospective birth cohort study examined the effects of low-dose chemical exposure in 164 pregnant women. Tissue from the placenta was analyzed for the enzyme CYP1A1 which changes endocrine disrupting chemicals into a form that can interfere directly with the body’s thyroid hormone receptors.

Researchers found that in pregnancies where the placenta contained higher amounts of the enzyme, the tissue also exhibited signs of thyroid disruption. Levels of two thyroid-regulated genes tended to be higher in these pregnancies, although the mother’s overall thyroid hormone levels did not change. The enzyme CYP1A1 cleans the blood and the body produces more of this enzyme when it is exposed to cigarette smoke. The researchers found pregnant women who smoked tended to have higher levels of the enzyme in the placental tissue.

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