Thyroid Alert: Low Iodine and Perchlorate Effects in Women

Abstract

Vol. 114, No. 12 EnvironewsOpen AccessThyroid Alert: Low Iodine and Perchlorate Effects in Womenis accompanied byUrinary Perchlorate and Thyroid Hormone Levels in Adolescent and Adult Men and Women Living in the United States Richard Dahl Richard Dahl Search for more papers by this author Published:1 December 2006https://doi.org/10.1289/ehp.114-a714aAboutSectionsPDF ToolsDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InReddit Perchlorate, an oxidizer in solid rocket fuel, is widely found in groundwater, drinking water, milk, vegetables, fruit, grain, and forage crops. Large doses of perchlorate have been shown to inhibit iodide uptake and reduce thyroid hormone production, which can contribute to metabolic problems in adults and abnormal neurodevelopment during gestation and infancy. Now, researchers at the CDC show that U.S. women with low iodine intake may be at risk for reduced thyroid function due to perchlorate exposure [EHP 114:1865–1871; Blount et al.].The researchers examined 2,299 men and women, aged 12 and older, who participated in the National Health and Nutrition Examination Survey. Examining the relationship between urine perchlorate concentrations and blood levels of the thyroid hormones thyroxine (T4) and thyroid-stimulating hormone (TSH), which stimulates T4, they observed that perchlorate was a significant predictor of thyroid hormone levels in women, but not in men.Upon seeing this sex-based difference, the authors then categorized 1,111 women into “sufficient” and “low” iodine groups using a threshold of 100 μg/L urinary iodine, based on WHO recommendations. They found a slight relationship between perchlorate concentrations and TSH for the sufficient-iodine group, but a much stronger one for perchlorate and both T4 and TSH in the low-iodine group.For the low-iodine group, higher perchlorate was associated with lower serum T4 and higher TSH. This relationship was consistent with what would be expected if perchlorate were inhibiting iodine uptake to such an extent that it interfered with thyroid hormone production. At the 50th percentile of urinary perchlorate (2.9 μg/L), the predicted decrease in T4 was 1.06 μg/dL; at the 95th percentile (13 μg/L), the predicted decrease in T4 was 1.64 μg/dL. Given that the normal range of T4 for women is 5–12 μg/dL, these predicted reductions were significant and indicate that even small increases in perchlorate exposure may inhibit the thyroid’s ability to absorb iodine.In the United States, 36% of women have urinary iodine levels under 100 μg/L. In addition, the perchlorate doses seen to cause effects in this study are well below the 24.5 ppb reference dose recommended in 2005 by a National Academy of Sciences panel. The authors say that another large study is needed to confirm these findings; they are planning that study.One thing leads to anotherThyroid tissue, with thyroglobulin, a protein used to produce T4, shown in orange. Perchlorate may interfere with iodide uptake by the thyroid, leading to altered thyroid hormone synthesis.FiguresReferencesRelatedDetailsRelated articlesUrinary Perchlorate and Thyroid Hormone Levels in Adolescent and Adult Men and Women Living in the United States5 October 2006Environmental Health Perspectives Vol. 114, No. 12 December 2006Metrics About Article Metrics Publication History Originally published1 December 2006Published in print1 December 2006 Financial disclosuresPDF download License information EHP is an open-access journal published with support from the National Institute of Environmental Health Sciences, National Institutes of Health. All content is public domain unless otherwise noted. Note to readers with disabilities EHP strives to ensure that all journal content is accessible to all readers. However, some figures and Supplemental Material published in EHP articles may not conform to 508 standards due to the complexity of the information being presented. If you need assistance accessing journal content, please contact [email protected]. Our staff will work with you to assess and meet your accessibility needs within 3 working days.