PCBs, Other Endocrine Disrupters, May Affect Fetal Brain Development: Study

New research suggests that certain common household chemicals may interfere with endocrine function, disrupting thyroid hormones during pregnancy and placing infants at risk before birth. 

Researchers from the U.S. and Canada conducted a prospective birth cohort study specifically focused on the role polychlorinated biphenyls (PCBs) have on pregnant women. They found PCBs interfere with the thyroid hormone action in pregnant women and it may travel across the placenta, affecting the fetus.

The findings were published in this month’s print edition of the Journal of Clinical Endocrinology & Metabolism.

The research was part of the GESTE study, a collaboration between a team of biologists led by R. Thomas Zoeller at the University of Massachusetts Amherst, and physician scientists led by Larissa Takser at the University of Sherbrooke Quebec.

Thyroid hormones are essential for normal human development. There are thyroid receptors in every cell of the human body.

Certain PCBs are metabolized by an enzyme in the body, CYP1A1, which can transform endocrine disrupting chemicals into a metabolite that can interfere directly with the body’s thyroid hormone receptors

PCBs were banned in the United States in 1979, but are still released into the environment from disposal sites and products manufactured prior to1979. PCBs were  used in many products, including flame retardant cloth, paint, adhesives, electrical transformers and even yellow dye.

Although banned decades ago, PCBs continue to be prevalent in many products across the country. A report released in 2013 revealed synthetic chemicals in industrial and household products, such as pesticides, electronics and cosmetics, contain many hormone disrupting chemicals, including PCBs.

Fetal Side Effects

In this latest study, researchers examined placental samples from 164 pregnant women with no thyroid disease. The placenta is the uterine structure that provides oxygen and nutrients to the fetus. Maternal and cord blood samples were taken at birth to measure thyroid levels.

They concluded PCBs interfere with the way the thyroid hormone functions, without changing the amount of hormone found in the body, which is exactly how doctors check for thyroid dysfunction.

Zoeller said this is the “strongest evidence to date” that endocrine disrupting chemicals can interfere with thyroid hormone action.

More so, the chemicals may affect thyroid hormones in pregnant women traveling across the placenta to affect the fetus. Researchers said this may have an impact on the brain development of an infant.

“Whatever is happening in the placenta likely reflects what is happening in the fetus,” said Zoeller. “To truly understand how endocrine-disrupting chemicals may be affecting pregnancies, the findings show we need to study not only hormone levels, but hormone activity at the cellular level.”

Pregnant women whose placentas contained higher levels of CYP1A1 also showed signs of thyroid disruption. Levels of 2 thyroid-regulated genes were higher in these pregnancies as well, despite the mother’s thyroid levels remaining the same.

Researchers warn this may be worse for those who smoke. The CYP1A1 enzyme’s primary task is to clean the blood. The body produces more of the enzyme when it is exposed to cigarette smoke. Pregnant women who smoked had much higher levels of the enzyme in their placental tissue, putting them at a higher risk of having thyroid disruption.

The study is the latest to link PCBs to newly discovered health concerns, despite a ban decades ago.

Exposure to PCBs may also increase a child’s risk of developing an autism spectrum disorder. A University of California, Davis study published in 2013 found PCBs promote neural irregularities, placing children at higher risk toward developing autism.

Research published earlier this year revealed PCB11, or yellow dye often used to color clothing and home goods, also poses a risk to human health.

Another study published in 2012 linked PCB exposure to decreased fertility. Couples with the highest levels of the toxins in their blood took much longer to conceive a child than those with lower amounts of PCBs.