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BPA lowered thyroid hormone levels in pregnant women, newborns
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Bisphenol A has been linked to changes in thyroid hormone levels in pregnant women and newborn boys, according to findings in a recently published study.
Jonathan Chevrier
Jonathan Chevrier, PhD, a research epidemiologist at the Center for Environmental Research and Children’s Health School of Public Health, University of California, Berkeley, and colleagues analyzed bisphenol A (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.
The researchers found that for each doubling of BPA levels, there was an associated decrease of 0.13 mcg/dL total thyroxine in mothers during pregnancy, which suggests a hypothyroid effect. For newborn boys, each doubling of BPA levels were linked to a 9.9% decrease in thyroid-stimulating hormone, indicating a hyperthyroid effect.
It was not clear why an association was not found among newborn girls, but animal studies may provide some clues. Results from one study in neonatal rats found a similar hyperthyroidic effect in males, but not females. Findings from 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.
“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,” Chevrier told Infectious Diseases in Children. “In addition, studies suggest that small changes in thyroid level, even if they’re within normal limits, may still have a cognitive effect.”
He also said although the results are intriguing, they are preliminary: “We need to spend a little more time trying to understand why we found a relation among boys but not girls. This being the first study of BPA and thyroid hormone in pregnant women and newborns, our results also need to be replicated in other populations before we can draw any conclusions.”
The researchers said several studies in recent years have linked lower thyroid hormone levels to delays in cognitive and motor development in young children.
Chevrier said there are ways to reduce BPA exposure, including:
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Avoiding any plastic with the number 7 inside the recycling sign;
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Avoiding putting plastic in the microwave; and
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Using powder rather than liquid infant formula.
Disclosure: The US 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. Chevrier reports no relevant financial disclosures.
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