Study Says Perchlorate is Thyroid Danger to Millions of Women

Researchers at the Centers for Disease Control and Prevention (CDC) have released findings that showed that American women -- and especially women with low iodine intake -- are at risk of hypothyroidism due to common exposure to the toxin perchlorate.

For years, there have been concerns about perchlorate's effect on the thyroid. (I've been covering it for two decades here at the About.com Thyroid Site.) The subject is controversial, however, as government regulators, environmental groups, citizen advocates, the military, and defense contractors responsible for the contamination have gone back and forth over the actual health effects, guidelines for safe standards, and how much perchlorate is acceptable in our food and water.

In a study released in 2005, a National Academy of Sciences panel determined that perchlorate affects the thyroid's ability to absorb iodine, but that the effects would only occur with exposure to high levels of perchlorate. This CDC study, however, shows that not only is perchlorate exposure pervasive, but for the first time, has demonstrated that even low levels of perchlorate exposure -- levels common to many Americans -- can have harmful health effects on the thyroid.

Perchlorate is a byproduct of rocket fuel production that has been found to contaminate parts of the nation's drinking water supply, as well as fruits, vegetables and grains irrigated by perchlorate-contaminated water, and milk and milk products from cows that grazed on contaminated grasses.

Perchlorate can inhibit the thyroid's ability absorb iodine from the bloodstream. Iodine is a building block of thyroid hormone. Low iodine levels, and/or the gland's inability to absorb iodine, can prevent the thyroid from producing enough thyroid hormone, resulting in an underactive thyroid -- hypothyroidism.

Hypothyroidism can cause weight gain, fatigue, depression, infertility, miscarriage, and is considered a risk factor for heart disease. Babies of mothers who are hypothyroid are at increased risk of cognitive and developmental problems, or, in more severe cases, cretinism and birth defects.

The CDC study looked at 2,299 men and women, aged 12 and older, who participated in the CDC's National Health and Nutrition Examination Survey (NHANES) during 2001-2002.

They evaluated the perchlorate concentrations in urine, along with the thyroid hormones thyroxine (T4) and thyroid-stimulating hormone (TSH) in the bloodstream. What the researchers found was that the presence of perchlorate was predictive of thyroid hormone levels in women -- but not men.

The researchers then focused on women in with higher-iodine levels, versus a lower-iodine group. In women with higher-iodine levels, they found a slight connection between perchlorate levels and TSH. But in the lower-iodine women, there was a strong connection between perchlorate levels, and elevated TSH and low T4 -- indicative of hypothyroidism.

Women who are pregnant are at particular risk because pregnancy already puts a strain on thyroid function, and sufficient thyroid function is necessary to maintain the pregnancy, as well as avoid cognitive or developmental problems in the baby. Women who are already slightly hypothyroid are also at greater risk, because the effects of the perchlorate may worsen their existing hypothyroidism.

According to the CDC, 36% of women in the U.S. have urinary iodine levels less than 100 µg/L, which was the lower-iodine level used for the study. Looking at those with lower iodine levels, as well as women who are pregnant, and those who are borderline hypothyroid already, the Environmental Working Group has concluded that an estimated 44 million American women are at heightened risk from perchlorate exposure.

How Much Perchlorate is a Risk?

According to the CDC, the median level of perchlorate found in urine was 2.9 micrograms per liter (a microgram per liter is equal to 1 part per billion). With average urine output at about 1.5 liters per day, this translates to around 5 micrograms of perchlorate per day being ingested. Even at this low level, there were negative effects seen on the thyroid.

The federal "safe dose" level, however, is almost ten times this dose.

According to the Environmental Working Group, the CDC has found that perchlorate levels in water as low as 3 parts per billion — think of one teaspoon of water in an Olympic-sized swimming pool — can have an effect on women's health.

What Can You Do?

Unfortunately, at the consumer level, it's very difficult to avoid perchlorate, as it's pervasive in our food and water supply. For example:

  • One EWG study found perchlorate in more than half of all store-bought winter lettuce samples
  • Another EWG study found perchlorate in 31 of 32 samples of milk in California
  • The California Department of Food and Agriculture found perchlorate in 32 out of 32 milk samples
  • According to tests conducted under the EPA's Unregulated Contaminant Monitoring Rule, at least 160 public water systems in 22 states are contaminated with perchlorate
  • Perchlorate can be found in domestic and imported produce, with highest levels frequently seen in oranges, grapes, raspberries, apricots, melons, lettuce, tomatoes, basil, kale, spinach and asparagus.
  • Overall, according to the CDC, 69 percent of the 1,090 food and beverage samples tested had detectable perchlorate.

According to the CDC, this widespread exposure in our water and food supply means that the typical American has a circulating level of perchlorate of 5.5 parts per billion.

To help protect your thyroid, you can make sure that you are not one of the almost four out of ten women with an iodine deficiency. A good daily multivitamin with iodine can ensure that you are getting the iodine you need. (But keep in mind, if you are one of the people who are NOT iodine deficient, excess iodine may aggravate and even worsen hypothyroidism and thyroid conditions. (For more information on the issue of how much iodine is too much, read The Iodine Controversy: Too Much vs. Not Enough, and What It Does To Your Thyroid?)

This is also an issue that calls out for citizen action. For example, at the national level, there is no drinking water standard for perchlorate. The only national oversight is FDA guidance suggesting cleanup be undertaken at a level of 24.5 ppb. A federal advisory committee on children's health has severely criticized that standard, however, warning that it may result in exposures that pose neurodevelopmental risks to infants and young children.

At the state level, the only state that currently has a drinking water standard for perchlorate is Massachusetts, which set their standard at 2 parts per billion in July of 2006. As of October 2006, California and New Jersey are considering standards of 6 ppb and 5 ppb.

Contact your state legislators and urge them to adopt stringent perchlorate standards for your state's water supply. And urge your federal legislators to adopt a national standard. (EWG recommends that the federal government set a drinking water standard of no more than 0.1 parts per billion of perchlorate). Also, urge federal legislators to mandate perchlorate cleanups at contaminated military bases and aerospace plants. Mandatory cleanup of existing contamination sites, and remediation of contaminated water supplies are the only ways to reduce perchlorate exposure.

Renee Sharp, an EWG analyst who has studied the chemical since 2000, summed it up, saying:

The Pentagon and defense contractors, who are responsible for much of the perchlorate in drinking water supplies, have lobbied hard against federal standards, arguing that perchlorate posed no threat to healthy adults. This new study shows that even very small levels of perchlorate in water or food can have a marked effect on thyroid levels in women. We can't ignore this serious public health issue any longer.

Sources

Blount, Benjamin C. et. al. "Environmental Health Perspectives: Urinary Perchlorate and Thyroid Hormone Levels in Adolescent and Adult Men and Women Living in the United States," Environmental Health Perspectives Branch (EHPB), National Institute of Environmental Health Sciences, National Institutes of Health, U. S. Department of Health and Human Services, Published October 5, 2006, Online

"44 Million Women at Risk of Thyroid Deficiency From Rocket Fuel Chemical," Environmental Working Group Press Release.

Environmental Working Group Analysis.

Shomon, Mary. "Perchlorate in Your Drinking Water," About.com, Online

Shomon, Mary. "Perchlorate and the Thyroid," About.com, Online

Shomon, Mary. "Perchlorate & its Danger to the Thyroid," About.com, Online

Shomon, Mary. "The Iodine Controversy: Too Much vs. Not Enough, and What It Does To Your Thyroid?" About.com, Online

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