Comparison of Iodine Concentrations in Kitchen Salt and Urine with the Thyroid Volume of Schoolchildren from Ribeirão Preto, São Paulo, Brazil: Warning of Worsening After 10 Years of Study.

BACKGROUND: In 2007 and 2015, two studies were conducted in Ribeirão Preto, São Paulo, Brazil, on schoolchildren of both sexes attending schools of three different socioeconomic levels (school 1: low; school 2: middle; school 3: high).

METHODS: Iodine concentrations were measured in samples of kitchen salt from the home provided by the schoolchildren and in urine samples, and these levels were compared to the thyroid volume by clinical assessment.

RESULTS: In 2007, a marked discrepancy in iodine concentrations was found in salt samples in 300 schoolchildren of both sexes (age range 8-10 years). Urinary iodine excretion >100 μg/L was detected in all cases, and 55.2% had concentrations of >300 μg/L (considered to be the upper limit by the World Health Organization). There was no increase in thyroid volume among the schoolchildren. In 2015, after a change in the norms for salt iodination from 20-60 to 15-45 mg/kg, the study was repeated in 295 schoolchildren (age range 8-10 years) from the same three schools studied previously. An improved standardization of iodine concentration was observed in the salt samples provided by the children, as well as a significant reduction in ioduria, with 10.9% of the samples showing an iodine concentration of <100 μg/L and with a reduction to 30.5% of samples with >300 μg/L. An increase in thyroid volume was also observed in a greater proportion of children from school 1, with a 7.92%, 5.19%, and 0.85% prevalence of goiter at schools 1, 2, and 3, respectively.

CONCLUSIONS: Despite the limitations of the present study, which include sample size and thyroid evaluation by palpation, it is inferred that the iodination of the Ribeirão Preto schoolchildren studied is adequate. However, the individual iodine intake of some students was <100 μg/L, and some students also had an increased thyroid volume, raising the possibility of a deterioration of iodine intake in 2015 compared to 2007.