Chemical found in food could harm women's thyroid

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Minute traces of perchlorate, a toxic chemical used in rocket fuel and widely found in food, water and soils throughout the country, may suppress thyroid function in millions of women, a new study by the Centers for Disease Control and Prevention suggests.

CDC researchers themselves were surprised to discover that such small quantities of the chemical --- as low as a few parts per billion --- were associated with measurable effects on thyroid hormone levels in so many women. There was no evidence that similar levels suppressed thyroid function in men.

"High levels of perchlorate have been known to affect thyroid function before, but this is the first time we have seen effects on thyroid function associated with the low levels of perchlorate exposure common in the general population" Dr. James Pirkle, deputy director for science of CDC's Environmental Health Laboratory, said Friday.

A second CDC study, due for release this week, will report that researchers found measurable levels of perchlorate in the urine of every man, woman and child they tested in a nationally representative sample.

The latest findings, reported in the journal Environmental Health Perspectives, add new fuel to a simmering controversy that began when perchlorate was first discovered in ground water at some California Superfund sites 20 years ago.

Traces of the chemical, which is also used in fertilizers, fireworks, road flares and explosives, have since been found in the water in 35 states, including Georgia, as well as in fruits, vegetables, beer, wine and milk.

Pirkle says the current study, which looked at a nationally representative sample of 2,299 Americans, also found that low levels of the chemical appear to have only modest effects on women who get sufficient amounts of dietary iodine from iodized salt or seafood.

But the CDC researchers did find a heightened risk of thyroid suppression in the 36 percent of the women who had lower levels of dietary iodine intake --- potentially 44 million individuals.

In those women, perchlorate exposure was associated with --- a "small to moderate" effect on levels of thyroid hormones. Chronic low levels of thyroid hormone, a condition called hypothyroidism, causes fatigue, weakness, cold intolerance, and other symptoms in adults and developmental defects in fetuses.

Pirkle says the health risk for such women can be minimized by increasing iodine consumption to roughly equivalent to a half teaspoon of iodized salt a day. The presence of measurable health risks from food and drinking water, however, quickly brought a call for government action to reduce public exposure.

"This new study shows that even small levels of perchlorate in water or food can have a marked effect on thyroid levels in women," said Renee Sharp, of the Environmental Working Group. "We can't ignore this serious public health issue any longer."

The Environmental Protection Agency has been studying possible limits on levels of perchlorate in drinking water for several years, but has been stymied by the lack of information about the health effect of low levels of the chemical.

In the wake of reports earlier this year that the Bush administration was delaying release of the CDC study, Sharp's group urged CDC Director Julie Gerberding to speed the release of data "so clearly needed to protect the public."