In China 30 years ago, there were many thyroid diseases, especially “big neck disease” (endemic goiter or nodular goiter); in the 1990s, our government started to implement the policy of supplemental iodized salt, and after a period of time, “big neck disease” was reduced; however, in recent years But in the past 10 years, thyroid disease has increased again! Why is this? First of all, the lack of iodine in food is the main factor that causes nodular goiter (great neck disease), which leads to the increase of the incidence of the disease. In China before the reform and opening up, especially in remote areas and highland mountainous areas, there was still poverty and backwardness, and the iodine in the soil was lost by washing, and the lack of transportation led to the lack of seafood. This is why the disease is also called “endemic goiter”. After the reform and opening up, the standard of living in China gradually improved and it was realized that “big neck disease” could be prevented by adding a certain amount of potassium iodide or sodium iodide to salt to reduce the occurrence of “big neck disease” among thyroid diseases. Therefore, our government responded to the call of the World Health Organization and implemented universal iodized salt supplementation, i.e., the sale of iodized salt through government action; after such a phase, the number of “big neck disease” did decrease. However, the incidence of thyroid cancer, Hashimoto’s thyroiditis, and nodular goiter is very high, especially in coastal areas.