Thyroid size and goiter prevalence after introduction of iodized salt: a 5-y prospective study in schoolchildren in...

The long-term goal of salt iodization is elimination of iodine deficiency and reduction of the goiter rate to < 5% in school-aged children. Normalization of the goiter rate probably indicates disappearance of iodine deficiency disorders as a public health problem. However, thyroid size may not return to normal for months or years after correction of iodine deficiency.

We described the time course and pattern of changes in thyroid size and goiter rate in response to the introduction of iodized salt in an area of severe endemic goiter.

In a 5-y prospective study, we measured thyroid size by ultrasonography and urinary iodine and thyroid hormone concentrations in schoolchildren 6 mo before the introduction of iodized salt and annually for 4 y thereafter.

Four years after the introduction of iodized salt and normalization of the median urinary iodine concentration, mean thyroid size had decreased 56% (P < 0.0001). However, 29% of the children remained goitrous, with a significant age shift in the distribution of goiter. At baseline, the goiter rate was significantly higher in younger (age: 5-9 y) than in older (age: 10-14 y) children (P < 0.0001). At 2, 3, and 4 y after salt iodization, the goiter rate was significantly higher in the older than in the younger children (at 4 y: 52% compared with 19%), and the difference increased with time (P < 0.0001).

The goiter rate in school-aged children may remain sharply elevated for up to 4 y after successful introduction of iodized salt, primarily because of persistent goiter in older children.