Thyroid in girls may be impacted by household chemicals

June 2 (UPI) -- In a first-of-its-kind study, researchers at Columbia University have found a link between exposure to phthalates and depressed thyroid function in young girls.

Phthalates are a class of chemicals known to disrupt the endocrine system and are found in numerous consumer products, including plastic toys, shampoos and household building materials.

The study is the first to assess the link between phthalate exposure and thyroid function in children over time. Results appear the journal Environment International.

Thyroid problems are more prevalent in women than in men, which may explain the link between phthalate exposure and depressed thyroid function in girls.

Prior studies have found an association between prenatal exposure to phthalates and a risk of lower IQ at age 7, mental and motor development delays in preschool children, and childhood asthma.

"The thyroid acts as the master controller of brain development," Pam Factor-Litvak, a professor of Epidemiology at the Mailman School, said in a press release. "Thyroid hormones set the schedule, and if the timing is out of synch, there may be later consequences in the brain. The thyroid disruptions we see in this study, although they fall within the normal range, could explain some of the cognitive problems we see in children exposed to phthalates and we are currently investigating that. As we know from lead, even small exposures can make a big difference."

Researchers at Columbia University's Mailman School of Public Health measured the levels of five phthalates and two thyroid hormones from 229 women during pregnancy and 229 children at age 3 enrolled in the Mothers and Newborns Study at the Columbia Center for Children's Environmental Health.

Lower levels of the active thyroid hormone free thyroxin, or FT4, were associated with metabolites of mono-n-butyl phthalate, or MnBP, mono isobutyl phthalate, or MiBP, monobenzyl phthalate, or MBzP, and monoethyl phthalate, or MEP, in girls.

Researchers found that prenatal exposure to phthalates did not significantly affect thyroid function at age 3, but that maternal thyroid function could have played a role since the fetus gets thyroid hormones through the mother.

The study did show prenatal exposure to a metabolite of Di (2- ethylhexyl) phthalate was associated with elevated levels of FT4, a finding they say suggests phthalates affect thyroid function differently depending on age of exposure.

"Going forward, it's important to learn what phthalates do to harm children, as well as the route by which this harm is inflicted," Factor-Litvak said. "Our overarching goal is to protect the health of future generations."

The study was {link:published in Environment International : "http://www.sciencedirect.com/science/article/pii/S0160412017302143" target="_blank"}.