Despite concerns that common fireproofing chemicals could disrupt thyroid function in developing fetuses, a new study finds no link between thyroid hormone levels and flame retardants in the blood of newborn babies.

Polybrominated diphenyl ethers, or PBDEs, leach out of common household items, such as carpets and couch cushions, and are absorbed by people. Detectable in the blood of 97 percent of Americans, the chemicals have been linked to a range of complications, including disrupted thyroid function in pregnant women.

There has been concern that would disrupt their developing babies' thyroids, too, potentially harming the infants' brain development. But California researchers who looked at PBDE levels in nearly 300 pregnant women, and in their babies after birth, found no relation between the mothers' chemical load and the newborns' thyroid hormone levels.

Jonathan Chevrier, the lead author and a research epidemiologist at UC Berkley's Center for Environmental Research and Children's Health, said the findings are not necessarily reassuring for pregnant women across the U.S.

Levels of exposure were ... low in our participants relative to the general U.S. population, and experimental studies conducted in animals suggest that prenatal exposure to (the chemicals) at high levels affect thyroid function in offspring, Chevrier told Reuters Health in an email.

Chevrier also authored an earlier study that did find a relationship between the chemicals and pregnant mothers' thyroid hormone levels. He said the difference between finding a relation between the chemicals and the hormones in mothers versus in their newborns may be timing.

I can only speculate here, Chevrier cautioned. Thyroid function had not completely matured in neonates when (the hormone) was measured by the Newborn Screening Program. So it is possible that a relation may be found in older children....

The new study, published in the American Journal of Epidemiology, used existing samples from 289 pregnant women in California's Salinas Valley and their babies, as well as medical records.

Chevrier and his colleagues analyzed the women's blood to find how much of the fireproofing chemicals it contained during their pregnancies, then did the same with samples of the infants' blood collected about one day after birth.

With the exception of one member of the PBDE chemical family -- brominated diphenyl ether 153 -- the mothers' blood levels of flame retardants showed no connection with levels of thyroid stimulating hormone, a sign of thyroid function. Even in the case of the one exception, the association was not statistically significant, which means it could have been due to chance.

A number of other studies have focused on whether the flame retardants harm children, and some have made that connection.

A 2010 report from the Columbia University Mailman School of Public Health, for example, found a link between higher levels of the fire retardants in umbilical cords and children's performance on tests later in life.

Julie Herbstman, author of that study and assistant professor at the Mailman School, said that some types of flame retardants are being phased out, but that does not eliminate the threat because products sold in the past remain impregnated with the chemicals.

Just because things are being phased out of production doesn't necessarily mean that exposure is going to go down, Herbstman told Reuters Health.

She said people are concerned that the chemicals may enter the environment once old household items end up in landfills and start breaking down.

According to Chevrier, there is still too little known about how the chemicals enter into a person's body, but the best guess is by ingesting everyday dust.

What some people are worried about is that the cycle of exposure might move from dust to dietary, said Herbstman. Once these things end up in the food supply, the exposure might change.

Chevrier added that going forward, it is important to test chemicals that might be released into the environment before they are used to see if there are any negative effects on human health.

This is true of chemicals that are used to replace (the flame retardants), on which we have very little information.

SOURCE: American Journal of Epidemiology, November 15, 2011.

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