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Effects of Six Months of Daily Low-Dose Perchlorate Exposure on Thyroid Function in Healthy Volunteers

Section of Endocrinology, Diabetes, and Nutrition (L.E.B., E.N.P., X.H., S.P.), Boston University Medical Center, and Department of Laboratory Medicine (B.M.), Boston Medical Center, Boston, Massachusetts 02118; Gradient Corp. (M.S., B.B.), Cambridge, Massachusetts 02138; Division of Laboratory Sciences (B.C.B.), National Center for Environmental Health, Centers for Disease Control and Prevention, Atlanta, Georgia 30333; and Jerry L. Pettis Memorial Veterans Administration Medical Center (A.F.), Loma Linda, California 92357

Address all correspondence and requests for reprints to: Lewis E. Braverman, M.D., Boston University Medical Center, 88 East Newton Street, Evans 201, Boston, Massachusetts 02118. E-mail: lewis.braverman{at}bmc.org.

Context: Perchlorate has been detected in U.S. drinking water supplies at levels ranging from 4 to 200 µg/liter as well as in agricultural products. Perchlorate is known to be a competitive inhibitor of iodine uptake by the thyroid through the sodium-iodide symporter.

Objective: The objective of the study was to determine whether prolonged exposure (6 months) to low levels of perchlorate would perturb thyroid function.

Design: This was a prospective, double-blinded, randomized trial.

Participants: The study population consisted of 13 healthy volunteers.

Intervention: Interventions included placebo vs. 0.5 mg or 3.0 mg potassium perchlorate daily.

Main Outcome Measures: Serum thyroid function tests, 24-h radioactive iodine uptake, serum thyroglobulin (Tg), urinary iodine and perchlorate, and serum perchlorate were measured.

Results: Mean urinary perchlorate value during ingestion of 0.5 mg perchlorate daily was 332.7 ± 66.1 µg per 24 h or 248.5 ± 64.5 µg/g creatinine and mean values for the four subjects who received 3 mg perchlorate daily were 2079.5 ± 430.0 µg per 24 h or 1941.7 ± 138.5 µg/g creatinine. There was no significant change in the thyroid ¹²³I uptakes during perchlorate administration. There were no significant changes in serum T₃, free T₄ index, TSH, or Tg concentrations during the exposure period, compared to baseline or postexposure values. Urine iodine values for the 3-mg perchlorate group were higher, but not significantly so, at baseline than during perchlorate exposure.

Conclusions: We observed that a 6-month exposure to perchlorate at doses up to 3 mg/d had no effect on thyroid function, including inhibition of thyroid iodide uptake as well as serum levels of thyroid hormones, TSH, and Tg.

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