Perchlorate is known to suppress thyroid function by inhibiting uptake of iodide by the human thyroid at doses of 200 mg/day or greater. A study was conducted to investigate the potential effects of perchlorate in drinking water on thyroid function in newborns and school-age children. A total of 162 school-age children and 9784 newborns were studied in three proximate cities in northern Chile that have different concentrations of perchlorate in drinking water: Taltal (100 to 120 micrograms/L), Chañaral (5 to 7 micrograms/L), and Antofagasta (non-detectable: < 4 micrograms/L). Among schoolchildren, no difference was found in thyroid-stimulating hormone levels or goiter prevalence among lifelong residents of Taltal or Chañaral compared with those of Antofagasta, after adjusting for age, sex, and urinary iodine. No presumptive cases of congenital hypothyroidism were detected in Taltal or Chañaral; seven cases were detected in Antofagasta. Neonatal thyroid-stimulating hormone levels were significantly lower in Taltal compared with Antofagasta; this is opposite to the known pharmacological effect of perchlorate, and the magnitude of difference did not seem to be clinically significant. These findings do not support the hypothesis that perchlorate in drinking water at concentrations as high as 100 to 120 micrograms/L suppresses thyroid function in newborns or school-age children.

The variations in plasma levels of TSH, T4, T3, and rT3, during the pubertal period, were studied in 647 school students from the urban area of Santiago in Chile (47% males and 53% females) with ages ranging between 7.5 and 15 yr. The subjects were grouped by age in consecutive intervals of 6 months each, and pubertal development was determined in every subject. TSH showed a significant increase, reaching a peak in the 9- to 9.5-yr interval. The same was found for T3 and T4, which reached a peak by 10 and 11 yr. The T4/T3 ratio did not show any significant variation with age. After 9.5 yr, a decrease in rT3 and increase in the T4/rT3 ratio was found. The TSH peak preceded the onset of clinical pubertal development, while the T3 and T4 peaks coincided with this onset. The variations in rT3 suggest an increase of peripheral conversion of T4 to T3. These transient events, not described until now, could be termed thyroidarche and could have a significant effect on pubertal growth and development.