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Early phthalate exposure diminishes thyroid function in young girls
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Young girls’ thyroid function may be suppressed after early childhood exposure to specific phthalates, whereas effects of exposure are not as pronounced in boys, study data show.
“The thyroid acts as the master controller of brain development,” Pam Factor-Litvak, PhD, professor of epidemiology at Columbia University’s Mailman School of Public Health, 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.”
Factor-Litvak and colleagues evaluated data from the Columbia Center for Children’s Environmental Health (CCCEH) study to determine whether an association exists between thyroid function in preschool-aged children and prenatal and childhood exposure to five phthalates, including di-n-butyl phthalate, di-isobutyl phthalate, butylbenzyl phthalate, diethyl phthalate and di(2-ethylhexyl) phthalate.
Researchers evaluated 229 children at aged 3 years who had urinary phthalate metabolites and serum free thyroxine and thyroid-stimulating hormone levels measured, and 181 mother-child pairs who had maternal urinary phthalate metabolites measured at the end of pregnancy and child thyroid hormones measured at age 3 years (prenatal sample). There was an overlap of 143 children between the child and maternal-child samples.
At age 3 years, child concentrations of mono(2-ethyl-5-hydroxyhexyl) phthalate (MEHHP), monobenzyl phthalate (MBzP), monoethyl phthalate (MEP), mono(2-ethyl-5-oxy-hexyl) phthalate (MEOHP) and mono-2-ethyl-5-carboxy-pentyl phthalate (MECPP) were higher in black children compared with Dominican children after adjustment for specific gravity. In the prenatal sample, black women had higher concentrations of MBzP compared with Dominican women, whereas MEHHP and MECPP were significantly higher in Dominican women compared with black women.
In the child sample, after controlling for specific gravity, sex and ethnicity, free T4 was significantly inversely associated with loge mono-n-butyl phthalate (MnBP). Free T4 in girls was significantly associated with loge MEHHP, loge MnBP, loge mono-isobutyl phthalate (MiBP), loge MEP and loge MEOHP. No significant association was observed between TSH and phthalate metabolite concentrations.
In the prenatal sample, child free T4 was significantly and positively associated with loge mono(2-ethylhexyl) phthalate (MEHP).
In the cohort that participated in both the child and maternal-child samples, child loge MnBP was inversely associated with free T4 in the total sample and in girls after controlling for prenatal MnBP. Free T4 in girls was inversely associated with child loge MEP after controlling for prenatal loge MEP.
“The CCCEH study results suggest that childhood urinary concentrations of phthalate metabolites (MnBP, MBzP, MiBP, MEHHP and MEP) may be associated with lower [free T4] in preschool-age minority children,” the researchers wrote. “Further, these findings were stronger in females. We only found limited evidence that urinary concentrations of MEHP in the late prenatal period are positively associated with increased concentrations of [free T4]. Our results contribute to a growing body of literature suggesting that early life exposure to some phthalates may affect endocrine function in children.” – by Amber Cox
Disclosure: The researchers report no relevant financial disclosures.
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