Perchlorate not tied to pregnancy thyroid problems

Everyday exposure to perchlorate, an industrial chemical found in drinking water and a range of foods, may not impair thyroid function in pregnant women, a new study suggests.

“Our data are reassuring,” lead researcher Dr. Elizabeth N. Pearce, of Boston University School of Medicine, told Reuters Health in an email. “Although low-level perchlorate exposure was ubiquitous in the pregnant women we studied, perchlorate exposure was not associated with alterations in their thyroid function.”

Perchlorate is used to manufacture rocket propellant, fireworks, flares and explosives. It is also found as an impurity in some industrial and consumer products, like cleaners and bleaches. In the environment, perchlorate is found at low levels in drinking water and foods such as milk, wheat and a range of fruits and vegetables, and a 2002 U.S. government study found perchlorate in urine samples from all 2,820 adults included.

In the body, sufficiently high levels of perchlorate slow down the transport of iodine to the thyroid gland, which churns out hormones that regulate metabolism and requires iodine. So there are concerns that perchlorate exposure could impair thyroid function - an effect that would be particularly troubling during pregnancy, as adequate thyroid hormone is necessary for fetal brain development.

A 2006 study by the U.S. Centers for Disease Control and Prevention (CDC) found that among women with moderately low iodine levels, those with relatively higher concentrations of perchlorate in their urine had lower thyroid hormone levels.

But in the new study, researchers found no relationship between urine perchlorate levels and thyroid function among more than 1,600 pregnant women who were typically iodine-deficient.

Because the women were deficient in iodine, they should, in theory, have been especially susceptible to any thyroid effects of perchlorate, noted Pearce.

More research is still necessary, however. One question that Pearce and her colleagues are currently studying is whether everyday perchlorate exposures have any effects on breastfeeding women and their infants.

Right now, the U.S. Environmental Protection Agency (EPA) is considering whether it should regulate perchlorate in drinking water. Two states, California and Massachusetts, have already issued their own drinking-water standards for the chemical.

“The EPA and other regulatory agencies will take all of the available data into account in determining what levels of exposure are safe,” Pearce said.

She and her colleagues based their findings on tests of 1,641 UK and Italian women who were in their first trimester of pregnancy and taking part in a study on thyroid function screening.

Tests showed that 635 women had low thyroid hormone concentrations, while the rest had normal levels. Overall, Pearce’s team found no correlation between the women’s urine perchlorate levels and their thyroid hormone levels.

It’s not clear why the findings differed from those of the earlier CDC study, which included mainly non-pregnant women, Pearce said. Further research, she and her colleagues write, is needed to understand the reasons.

SOURCE: Journal of Clinical Endocrinology & Metabolism, online April 28, 2010.

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