Six months of exposure to perchlorate at doses of up to 3 mg per day does not alter thyroid activity, study findings from the USA reveal.
Perchlorate salts have been used in products such as pharmaceuticals, explosives, and fireworks for many years. In addition, perchlorate has been detected in drinking water in the USA since 1997 at levels ranging from 4-200 μg, and in lettuce and milk, the scientists comment.
However, perchlorate is a competitive inhibitor of thyroid iodine uptake, and "prolonged major inhibition of iodine uptake can result in decreased synthesis of thyroid hormones," the authors write in the Journal of Clinical Endocrinology & Metabolism.
"In view of the reported environmental perchlorate contamination, the potential health effects from this relatively low level perchlorate ingestion are a matter of public health interest," they stress.
To explore this issue, the research team, led by Lewis Braverman from Boston University Medical Center in Massachusetts, administered 0.5mg or 3.0mg of perchlorate or placebo daily in drinking water to 13 healthy volunteers for 6 months.
Examinations showed that there were no significant changes in serum triiodothyronine, free thyroxine index, thyroid stimulating hormone or thyroglobulin concentrations during the perchlorate exposure period compared with baseline or values after perchlorate exposure.
Reflecting on this data, the authors therefore conclude: "6-month exposure to perchlorate 0.5 and 3.0 mg/day had no effect on thyroid function."
They add: "The results suggest that healthy, euthyroid individuals, with normal levels of iodine intake, can tolerate chronic exposure to perchlorate at doses up to 3 mg/day without any effects on thyroid function, including inhibition of iodine uptake."