When California set fire safety standards in the 1970s that allowed manufacturers to use chemical flame retardants to bulk up their products by up to 20 percent, it wasn’t long before they started to appear elsewhere. One particular type, polybrominated diphenyl ethers (PBDEs), are now on the surfaces of our food, air, dust, and furniture. California eventually wrote PBDEs out of its standards for health and environmental concerns, including the growing number of studies pitting PBDEs as carcinogens. While the use of these chemicals has declined since new standards were issued, exposure persists, and it could spell trouble for women’s health.

Prior research has suggested that exposure to PBDEs can negatively affect the thyroid, a butterfly-shaped gland at the base of the neck. It creates hormones that are considered essential for the function of every cell in the human body. Even the slightest change to hormone levels can result in adverse health effects such as cancer, and kidney, liver, and heart disease. One idea is that the chemicals mimic the effects of estrogen, which is not a good thing for thyroid function; it may disturb hormone expression and possibly promote cell proliferation and tumor growth. And yet, the authors of a new study published in Environmental Health found “no research related to the potential sensitivity of menopausal women to thyroid disease based on PBDE concentration.” They took it upon themselves to bridge this gap in knowledge.

The researchers analyzed data collected from a nationally representative sample of women involved in the National Health and Nutrition Examination Survey. They compared the levels of PBDEs in participants’ blood samples to their histories of thyroid problems like hyperthyroidism or Hashimoto's thyroiditis.

Overall, women were five times more likely than men to be told by a doctor that they had thyroid-related disease, an effect that doubled in postmenopausal women. Women with higher concentrations of PBDEs in their blood were also significantly more likely to have such disease than those with lower amounts. These results fuel the existing idea that women bear the burden of this type of disease compared to men.

"To our bodies, these flame retardant chemicals look and function exactly like endogenous hormones our bodies produce,” lead study author Joseph Allen, assistant professor of exposure assessment science at Harvard Chan School, said in a press release. “Should we be surprised that we see downstream health effects for women with higher body burdens of these chemicals? I think no. This is all too predictable and preventable.”

Experts may have suspected as much, but according to the researchers, this is the first paper to suggest a link between PBDEs and an increased risk in thyroid disease. They found it particularly striking that this association was so much higher in postmenopausal women. One idea for the difference has to do with PBDEs strong ability to bind to both estrogen and thyroid hormones, which can interfere with the change in estrogen levels associated with menopause.

The researchers suspect that when there is less estrogen in the system, the chemicals compete for “binding sites that are critical for the removal of circulating estrogen produced by other tissues, leading to higher than expected levels of circulating estrogen.” PBDEs also have a strong affinity for serum thyroxine binding globulin, a protein that moves thyroid hormones throughout the body, the researchers said; bonding with it may disrupt the way hormones are transported.

Taken together, the findings provide better insight to the impact PBDEs have on the thyroid. Allen and his colleagues call for additional research to confirm them when new blood samples are made available through the National Health and Nutrition Examination Survey.

Source: Allen JG, et al. PBDE Flame Retardants,Thyroid Disease, and Menopausal Status in U.S. Women. Environmental Health. 2016.