Objective: To study the annual incidence of thyroid diseases before and after the increase of iodized salt intake.
Method: A total of 26,010 persons were examined from mid August to the end of December in 1999.
Results: 1. Three hundred and ten patients of thyroid diseases were identified from 1990 to July 1999. One hundred and eighty-three patients were diagnosed after iodine supplementation. 2. The constitution of thyroid diseases had changed significantly regarding the increase of hyperthyroidism, simple goiter and thyroid nodule. 3. Fifty-five patients with hyperthyroidism including 39 patients (70.91%) receiving iodine supplementation were diagnosed. The average annual incidence of hyperthyroidism after iodine supplementation was 36.87 per 100,000, a three-time increase as compared with that before iodine supplementation. The incidence of hyperthyroidism began to show a significant rise in 1996. The year with highest annual incidence was 1997, remaining at high level after supplying iodized salt. Since then the annual relative risk for hyperthyroidism had been increasing.
Conclusion: The number of patients with thyroid diseases showed a significant increase after mass iodine supplement. At the same time, the spectrum of thyroid diseases had also changed. Iodized salt intake and the incidence of hyperthyroidism showed a significant correlation. However, the typical model of the change of disease patterns incidence needs further study.