Thyroid adaptation to chronic tetraglycine hydroperiodide water purification tablet use

Tetraglycine hydroperiodide tablets purify water by liberating 8 mg free iodine/tablet. The effects of ingesting four tablets daily for 3 months on thyroid size, function, and radioactive iodine uptake were studied prospectively in eight healthy volunteers. Serum inorganic iodide increased from 2.7 to approximately 100 micrograms/dL. Urinary iodide excretion rose 150-fold from a pretreatment mean of 0.276 to 40 mg/day. Radioactive iodine uptake was less than 2% after 7 days and remained below 2% in all subjects at 90 days. Mean serum T4 and T3 declined after 7 days. T4 remained below baseline, whereas T3 had recovered by the end of the treatment period. Serum TSH and the TSH response to TRH rose significantly after 7 days and remained elevated at 3 months. The average thyroid volume, determined by ultrasound, increased by 37%. Neither hyperthyroidism nor hypothyroidism was observed. The mean thyroid volume in seven subjects available for repeat determinations an average of 7.1 months after the study was not different from the baseline value. In normal subjects, a reversible TSH-dependent thyroid enlargement occurs in response to the iodine load from daily use of tetraglycine hydroperiodide water purification tablets.