Pregnant women exposed to higher levels of the chemical bisphenol A gave birth to baby boys with lower thyroid hormones, according to a new study published today.
The study by University of California, Berkeley, scientists is the first to link the ubiquitous chemical – used in hard plastics, canned food liners and some paper receipts – to altered thyroid hormones in babies, and it adds to evidence that BPA may have some effects on fetuses.
For every doubling of the mothers’ BPA levels, there was 9.9 percent less thyroid-stimulating hormone in their baby boys. No significant effect was detected in the girls; animal studies suggest females may be able to metabolize the chemical better.
“Most work up to this point has focused on [BPA’s] estrogen properties. The fact that it’s also messing up thyroid function is very surprising,” said Laura Vandenberg, a postdoctoral fellow at Tufts University who studies BPA but was not involved in the new study.
Experts said they do not know what, if anything, the reductions in thyroid hormones might mean for the health of the babies because their levels remained within the range considered normal. But previous research suggests that reduced thyroid hormones might impair learning abilities and motor skills.
“Thyroid hormone is probably the best known factor in terms of influencing brain development,” said Thomas Zoeller, a biology professor at University of Massachusetts-Amherst who specializes in studying thyroid hormones and brain development. “The fact that the researchers see relationships at all is a very important issue that we should not ignore."
The scientists analyzed data from 364 pairs of moms and newborns in California’s Salinas Valley, a low-income community of mostly Mexican-American farm workers. Most of the mothers had low levels of BPA – 42 percent less than the average U.S. woman. Eighty-two percent had the chemical in their urine, compared with 95 percent of women of childbearing age tested nationwide.
While the study does not prove that BPA alters babies' thyroid hormones, scientists say it provides evidence that the link should be further investigated.
“Our data suggest that there is not a safe level of exposure,” said Jonathan Chevrier, an assistant researcher at the University of California, Berkeley, Center for Environmental Research and Children's Health and lead author of the study, which was published in Environmental Health Perspectives.
The American Chemistry Council, which represents chemical manufacturers, maintains that BPA is safe to use and questioned the validity of the study.
"The author's speculation that BPA is linked to health effects caused by thyroid hormone levels in women and newborns is not supported by the data," said Steven Hentges, of the council's Polycarbonate/BPA Global Group, in a prepared statement. "The authors themselves note that the thyroid hormone levels reported were within normal range and the study was not designed to measure any health effects."
He also said the testing was too limited to be an accurate representation of the mother's levels during pregnancy.
Thyroid hormones are continually produced, and BPA doesn’t stay in people’s bodies for long, but Chevrier said this doesn’t mean the findings aren’t cause for concern.
“This effect we see might not be permanent…Some people might think that’s good news,” he said. “But people are continually exposed to BPA. The effect isn’t permanent, but people are permanently exposed.”
However, Zoeller cautioned that "because BPA is not bioaccumulative, it is very difficult to get a good sense of what exposure is."