Study finds link between BPA and thyroid hormone changes

Jonathan Chevrier, a scientist at the Berkeley Research Group in Methods for Occupational Epidemiology poses in his office on University Avenue.
Gracie Malley/Senior Staff
Jonathan Chevrier, a scientist at the Berkeley Research Group in Methods for Occupational Epidemiology poses in his office on University Avenue.

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Research coming in part out of UC Berkeley has found a correlation between a common household chemical and thyroid hormone levels in pregnant women and their newborn babies.

Bisphenol A, known as BPA, is commonly found in the inner lining of food and beverage cans, in hard plastics such as reusable water bottles and in chemical sealants.

The study measured the concentration of BPA in urine samples collected during the first and second half of pregnancies in 476 women, according to Jonathan Chevrier, a scientist at the Berkeley Research Group in Methods for Occupational Epidemiology who worked on the study.

By also examining levels of the thyroid hormone T4 and thyroid-stimulating hormone TSH in the women and their newborns, the researchers were able to identify a correlation between levels of BPA and thyroid hormone levels.

Chevrier said that once they had accounted for variables known to cause changes in thyroid levels, such as maternal age and demographic differences, the researchers found that pregnant women who had higher levels of BPA in their urine tended to have lower levels of T4, and their newborn boys tended to have lower levels of TSH.

Nearly 2.4 billion pounds of BPA were produced in 2007, and 95 percent of American women of reproductive age have detectable levels of it in their urine, according to Chevrier. Because of how easy it is to be exposed to the compound, BPA has been scrutinized by the public for its potential effects on humans.

“There are a lot of people who continue to doubt whether this chemical is harmful,” said Barbara Abrams, a UC Berkeley professor of epidemiology, maternal and child health and public health nutrition who was not involved in the study, in an email. “Given its widespread use and the fact that pregnant women and fetuses, the most vulnerable members in the population, are widely exposed, even the subtle negative changes in thyroid status found in this study suggest that future research to determine BPA’s impact on maternal and child health is urgently needed.”

While Abrams acknowledged the importance of the study, she was careful to note that the results of the study could not prove that BPA is the cause of the thyroid hormone changes in the pregnant women.

In a statement in response to the study, the American Chemistry Council maintained that it is safe to use BPA in food-contact materials.

“Not only have the U.S. Food and Drug Administration and Health Canada both recently reconfirmed that it is unlikely that BPA could cause human health effects, but the European Food Safety Authority and a World Health Organization panel have also supported the continued use of BPA in products that come in contact with food,” the statement reads.

The effects of BPA are also being examined in animals.

Thomas Zoeller, a professor in the biology department at the University of Massachusetts Amherst, has been doing research on how thyroid hormones affect development. He said that from his research, it appears that animals exposed to BPA experience a situation called “thyroid resistance” in which thyroid hormones seem elevated.

The study the Berkeley researchers were involved in, called Maternal Urinary Bisphenol A during Pregnancy and Maternal and Neonatal Thyroid Function in the CHAMACOS Study, was co-authored by Robert Gunier, Asa Bradman, Nina Holland, Antonia Calafat, Brenda Eskenazi and Kim Harley and was published Oct.  4 in the journal Environmental Health Perspectives.

Contact Pooja Mhatre at [email protected].

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