(Reuters Health) - 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: here Journal of Clinical Endocrinology & Metabolism, online April
28, 2010.
