Researchers from the University of California in Berkeley have found that a common flame retardant chemical can cause altered thyroid hormone levels in pregnant women. High levels of this chemical were found in their blood, and may be the cause of difficulty becoming pregnant.
The study checked women for PBDEs, or polybrominated diphenyl ethers, a class of chemicals that is used as a flame retardant in many household items. Carpeting, foam furnishings, electronics, and some plastics have traces of PBDEs in them. The use of these chemicals was implemented in the 1970s as part of the U.S. fire safety standards. Recent research has found, however, that these chemicals can leach out and build up in human fat cells.
“This is the first study with a sufficient sample size to evaluate the association between PBDE flame retardants and thyroid function in pregnant women,” said the study’s lead author, Jonathan Chevrier, a UC Berkeley researcher in epidemiology and in environmental health sciences. “Normal maternal thyroid hormone levels are essential for normal fetal growth and brain development, so our findings could have significant public health implications. These results suggest that a closer examination between PBDEs and these outcomes is needed.”
Estimates show that 97 percent of US citizens have levels of PBDEs in their blood, and many at 20 times higher than European counterparts. Those living in California often have the highest levels due to stricter fire safety codes in that state.
“Despite the prevalence of these flame retardants, there are few studies that have examined their impact on human health,” said the study’s principal investigator, Brenda Eskenazi, UC Berkeley professor of epidemiology and of maternal and child health. “Our results suggest that exposure to PBDE flame retardants may have unanticipated human health risks.”
Blood samples were taken from 270 women near the end of their second trimester of pregnancy. These women were chosen from subjects of a larger study by the Center for the Health Assessment of Mothers and Children of Salinas (CHAMACOS) that was studying environmental factors on reproduction. Outside factors, such as smoking, drinking, and pesticide exposure were factored for among the women. Researchers were still able to find 10 PBDE chemicals, two types of thyroxine (T4) and thyroid-stimulating hormone (TSH) in the blood samples.
The researchers found that higher levels of PBDEs was linked to decreases in the thyroid-stimulating hormones. The women that had low levels of the thyroid-stimulating hormone also had normal ranges of free T4. Researchers say this means that subclinical hyperthyroidism rates were higher in those with increased PBDE concentrations.
“Low TSH and normal T4 levels are an indication of subclinical hyperthyroidism, which is often the first step leading toward clinical hyperthyroidism,” said Chevrier. “Though the health effect of subclinical hyperthyroidism during pregnancy is not well understood, maternal clinical hyperthyroidism is linked to altered fetal neurodevelopment, increased risk of miscarriage, premature birth and intrauterine growth retardation.”
Other flame retardant chemicals, such as PentaBDE and octaBDE, have been banned by Stockholm Convention on Persistent Organic Pollutants, the European Union and eight U.S. states for the health risks they cause. However, many products made before 2004 have these chemicals still in them. The health impact of the chemicals being created to replace these flame retardants has not yet been studied. – Summer, Staff Writer
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