A new study from UC Berkeley has linked a mother's consumption of a chemical called bisphenol A (BPA) to a greater risk for an overactive thyroid in her newborn son.
"Most of the women and newborns in our study had thyroid hormone levels within a normal range, but when we consider the impact of these results at a population level, we get concerned about a shift in the distribution that would affect those on the borderline," lead author Jonathan Chevrier, a research epidemiologist at UC Berkeley's Center for Environmental Research and Children's Health, said in a press release. "In addition, studies suggest that small changes in thyroid level, even if they're within normal limits, may still have a cognitive effect."
BPA is an estrogen-like compound that is commonly found in hard plastics, linings of canned food, dental sealants and sales receipts on thermal paper. According to the U.S. Department of Health and Human Services, the chemical has been in use for more than 40 years, and was declared by the Food and Drug Administration (FDA) to be market safe.
However, studies have showed that BPA may have an effect on laboratory animals, even in low amounts. Further research conducted by the National Toxicology Program at the National Institutes of Health and FDA have concluded there is some worry that BPA may affect the brain, behavior and prostate gland in fetuses, infants and young children. Another recent study also tied high BPA levels to childhood obesity
BPA and obesity in kids: 3 facts
In July, the FDA formally banned BPA from baby bottles and sippy cups, but many manufacturers had been phasing the chemical out of these products in recent years.
This new research may show that the mother's consumption of BPA may affect her child. Researchers looked at BPA levels in urine samples of 335 women during the second half of pregnancy. Thyroid levels of the mother and newborn were determined using blood samples during pregnancy and a few days after birth, respectively.
Researchers found that every doubling of BPA levels in pregnant moms was tied to a decrease of 0.13 micrograms per deciliter of total thyroxine (T4), meaning their thyroids were less active. Boys whose mother's had doubled their BPA had a 9.9 percent decrease in thyroid stimulating hormone (TSH), meaning their thyroid was overactive.
Chevrier told the San Jose Mercury News that he believes because the mother's thyroid was less active, the newborn son's thyroid was working overtime to compensate for the loss.
Newborn girls were not observed to have any changes with thyroid levels. However, animal studies on rats showed females had a higher level of an enzyme important in metabolizing BPA.
Senior study author Kim Harley, adjunct associate professor of public health and associate director of CERCH, said in a press release that BPA is ubiquitous in our environment, with more than 90 percent of women of reproductive age having detectable levels in their urine. "Until we learn more about the human health effects of these chemicals, it would make sense to be cautious and avoid exposure when possible, particularly for those who are pregnant," she said
Tracey Woodruff, director of UCSF's Program on Reproductive Health and the Environment, said to the San Francisco Chronicle the study was especially important because it was the first to look at the chemicals effects on pregnant women. She was not involved with the research.
"This is one more study in the accumulating evidence that taking steps to avoid BPA would be prudent," Woodruff said to Mercury News.
The study was published in Environmental Health Perspectives on Oct. 4.
Public release date: 4-Oct-2012
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Contact: Sarah Yang
University of California - Berkeley
BPA linked to thyroid hormone changes in pregnant women, newborns
Berkeley � Bisphenol A (BPA), an estrogen-like compound that has drawn increased scrutiny in recent years, has been linked to changes in thyroid hormone levels in pregnant women and newborn boys, according to a new study by researchers at the University of California, Berkeley.
Normal thyroid function is essential to the healthy growth and cognitive development of fetuses and children. Yet, until this study, to be published Thursday, Oct. 4, in the journal Environmental Health Perspectives, little was known about the effects of BPA exposure on thyroid hormones in pregnant women and newborns.
The new findings add to growing health concerns about BPA, a chemical found in hard plastics, linings of canned food, dental sealants, and sales receipts on thermal paper, which is coated with a chemical that changes color when exposed to heat. In July, the U.S. Food and Drug Administration officially banned the chemical in baby bottles and cups, something the industry began doing voluntarily in recent years in response to consumer concerns about the potential risks of BPA.
The researchers analyzed BPA levels in the urine samples of 335 women during the second half of pregnancy, and thyroid hormone levels in blood samples taken from the mothers during pregnancy and from the newborns within a few days of birth. The participants were part of the Center for the Health Assessment of Mothers and Children of Salinas (CHAMACOS) study led by Brenda Eskenazi, UC Berkeley professor of epidemiology and of maternal and child health.
The researchers found that for each doubling of BPA levels, there was an associated decrease of 0.13 micrograms per deciliter of total thyroxine (T4) in mothers during pregnancy, which suggests a hypothyroid effect. For newborn boys, each doubling of BPA levels linked to a 9.9 percent decrease in thyroid stimulating hormone (TSH), indicating a hyperthyroid effect.
"Most of the women and newborns in our study had thyroid hormone levels within a normal range, but when we consider the impact of these results at a population level, we get concerned about a shift in the distribution that would affect those on the borderline," said study lead author Jonathan Chevrier, research epidemiologist at UC Berkeley's Center for Environmental Research and Children's Health (CERCH). "In addition, studies suggest that small changes in thyroid level, even if they're within normal limits, may still have a cognitive effect."
It was not clear why an association was not found among newborn girls, but animal studies may provide some clues. One study in neonatal rats found a similar hyperthyroidic effect in males, but not females. Another study found that female rats had higher levels of an enzyme important in metabolizing BPA when compared with their male counterparts. Whether that same relationship holds true for humans is not yet clear.
"In addition, studies in rodents are increasingly showing that BPA can have different effects in males and females, particularly in brain development and behavior," said the study's senior author, Kim Harley, adjunct associate professor of public health and associate director of CERCH.
The researchers pointed out that several studies in recent years have linked lower thyroid hormone levels to delays in cognitive and motor development in young children. Two years ago, the same group of UC Berkeley researchers also found links between PBDEs (polybrominated diphenyl ethers), a class of flame retardants, and changes in thyroid hormone levels.
They were confident that the BPA was acting on thyroid hormones independently from PBDEs, because levels of the two compounds were not correlated.
"There is good reason to be concerned about PBDEs and BPA, because both of these compounds are ubiquitous in our environment," said Harley. "More than 90 percent of women of reproductive age have detectable levels of BPA in their urine, and some 97 percent of U.S. residents have detectable levels of PBDEs in their blood. Until we learn more about the human health effects of these chemicals, it would make sense to be cautious and avoid exposure when possible, particularly for those who are pregnant."
Other co-authors of the study are Robert Gunier, Asa Bradman and Nina Holland from CERCH; and Antonia Calafat from the National Center for Environmental Health at the Centers for Disease Control and Prevention.
The U.S. Environmental Protection Agency, the National Institute for Environmental Health Sciences, the UC Institute for Mexico and the United States, and the UC Berkeley Center for Latino Policy Research provided support for this research.
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