Perchlorate Fact Sheet October 5, 2006

Study of Perchlorate Exposure and Thyroid Function in the U.S. Population

  • CDC researchers recently reported the results of a study on the relationship between exposure to low doses of perchlorate in the U.S. population and thyroid hormone levels. This study is the first to examine the relationship between perchlorate and thyroid function in women with lower urine iodine levels (levels less than 100 micrograms per liter). The study is also much larger than either of the two previous studies of perchlorate and thyroid function that targeted or included women.
  • The study involved 2,299 men and women aged 12 years and older. Researchers found an association between levels of perchlorate in urine and decreased thyroid function in women 12 years old and older.
  • The relationship was strongest in women with lower iodine intake, that is in women who had levels of iodine in their urine less than 100 micrograms per liter (µg/L).
  • The study did not find a similar association for men.
  • For women with lower iodine levels, perchlorate exposure was associated with small-to-moderate size changes in levels of thyroxine, the thyroid hormone which helps regulate the body’s metabolism and in levels of thyroid stimulating hormone (TSH), which is responsible for stimulating the production of thyroxine.
  • About 36% of women in the United States have these lower iodine levels.
  • Among women with higher levels of iodine in their urine (above 100 µg/L), CDC found a statistically significant association between perchlorate and TSH levels but not between levels of perchlorate and thyroxine levels.
  • The study was published on Oct. 5, 2006, in the peer-reviewed journal Environmental Health Perspectives. It is available online at

How Perchlorate Affects People’s Health

  • When perchlorate enters the body it can block the thyroid gland from taking up iodine. The thyroid gland needs iodine to make the thyroid hormones that regulate how the body uses energy.
  • Deficiency of iodine or conditions that prevent its use in making thyroid hormone lead to decreased amounts of thyroid hormone circulating in the blood, which can manifest as symptoms of hypothyroidism.
  • Maintaining sufficient intake of dietary iodine is important for good thyroid health. A good source of iodine is iodized salt. Only a small amount of iodized salt, about half a teaspoon per day, will supply an adequate amount of iodine.
  • Scientists continue to conduct research into the health effects of low-dose exposure to perchlorate. Sources of Perchlorate and How are People Exposed
  • Perchlorate is a chemical most commonly used in rocket fuel. The chemical is also used in explosives and fireworks. A combination of human activity and natural sources has led to the widespread presence of perchlorate in the environment.
  • People are exposed to perchlorate by drinking water or eating food containing perchlorate or by working in the manufacture of products containing perchlorate.

For More Information About Perchlorate

Page last reviewed: December 1, 2008