Effects of six months of daily low-dose perchlorate exposure on thyroid function in healthy volunteers.
BACKGROUND
Perchlorate has been detected in U.S. drinking water supplies at levels ranging from 4 to 200 microg/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.


METHODS
This was a prospective, double-blinded, randomized trial.


METHODS
The study population consisted of 13 healthy volunteers.


METHODS
INTERVENTIONs included placebo vs. 0.5 mg or 3.0 mg potassium perchlorate daily.


METHODS
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 microg per 24 h or 248.5 +/- 64.5 microg/g creatinine and mean values for the four subjects who received 3 mg perchlorate daily were 2079.5 +/- 430.0 microg per 24 h or 1941.7 +/- 138.5 microg/g creatinine. There was no significant change in the thyroid (123)I uptakes during perchlorate administration. There were no significant changes in serum T(3), free T(4) 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.
Braverman
Lewis E
LE
Boston University Medical Center, 88 East Newton Street, Evans 201, Boston, Massachusetts 02118, USA. lewis.braverman@bmc.org
Pearce
Elizabeth N
EN
He
Xuemei
X
Pino
Sam
S
Seeley
Mara
M
Beck
Barbara
B
Magnani
Barbarajean
B
Blount
Benjamin C
BC
Firek
Anthony
A
D000328:Adult; D000368:Aged; D004311:Double-Blind Method; D005260:Female; D006801:Humans; D007455:Iodine / Q000652:urine; D007457:Iodine Radioisotopes; D008297:Male; D008875:Middle Aged; D010472:Perchlorates / Q000008:administration & dosage* / Q000493:pharmacokinetics / Q000633:toxicity; D011446:Prospective Studies; D013954:Thyroglobulin / Q000097:blood; D013961:Thyroid Gland / Q000187:drug effects* / Q000502:physiology*; D013972:Thyrotropin / Q000097:blood; D013974:Thyroxine / Q000097:blood; D014284:Triiodothyronine / Q000097:blood
D007457:Iodine Radioisotopes; D010472:Perchlorates; D014284:Triiodothyronine; D013972:Thyrotropin; D013954:Thyroglobulin; D007455:Iodine; D013974:Thyroxine; C494474:perchlorate