Back in the 1960s, surveys in China showed that iodine nutrition deficiency was prevalent in most provinces and cities across the country, including the coastal areas of the Yangtze River Delta. To prevent and control endemic goiter and cretinism, China began to implement salt iodization and introduced a policy of universal iodine supplementation. With the popularization of iodized salt, by the early 1990s, the prevalence of endemic goiter and cretinism in the disease areas of Hebei and Northeast China was basically controlled. However, as the number of patients with thyroid disease was clinically found to increase, some people questioned whether the high incidence of thyroid disease was due to the excessive amount of iodized salt we eat on a daily basis. Should patients with thyroid disease be eating non-iodized salt? Iodine is an essential trace element for the human body and is the main raw material for the synthesis of thyroid hormones, which improve the metabolic activity of the body, promote physical growth and brain development, and maintain the normal physiological functions of the body. When the iodine reserve in the body decreases, the body synthesizes less thyroid hormone, resulting in insufficient metabolism and delayed growth and development. The main consequence of iodine deficiency is thyroid dysfunction, and the well-known “big neck disease” is one of the most typical conditions. In addition, iodine deficiency in children and adolescents can affect growth and development, resulting in intellectual and physical problems. Iodine deficiency in pregnant women can affect the brain development of the fetus and infant, and may cause irreversible mental retardation, such as cretinism (also called cretinism). The average daily intake of iodine for a normal adult is about 150 micrograms. In our daily diet, the amount of iodine in staple foods, fruits and vegetables is negligible. According to the survey, despite the habit of eating seafood in coastal areas of China, the amount of iodine taken from iodized salt still accounts for 63% of the total dietary iodine intake. It is difficult to achieve the standard daily intake of iodine by food intake. According to the average value of 25 mg/kg of iodized salt in China, 6-9 grams of salt per day is just enough to meet the recommended daily iodine intake of 150-300 micrograms. On the other hand, data from the Chinese Nutrition Society indicates that a daily iodine intake of 800 micrograms or less is generally safe. Therefore, residents in coastal areas do not need to worry about “iodine overdose” in their diet. Moreover, the data shows that with the consumption of qualified iodized salt, the dietary iodine intake and urinary iodine intake of various groups of people are basically appropriate and there is no so-called “iodine overdose”. According to a recent survey on iodized salt and iodine intake by the Shanghai CDC, the iodine content of iodized salt for Shanghai residents is appropriate, and most of the necessary iodine for the human body needs to be solved by iodized salt, and it is not enough to supplement iodine with food, including seafood. As for some reports that iodized salt is the main culprit of thyroid disease, I think they are overstating the case. There is no evidence of a correlation between iodine and thyroid disease, and the World Health Organization has concluded that the incidence of thyroid cancer is lower in areas with adequate iodine intake than in areas with iodine deficiency. Nor is there a significant increase in the number of patients with clinical hyperthyroidism as some reports suggest. In recent years, however, the number of patients with thyroid nodules has increased, and I believe that the high prevalence of thyroid screening today has led to an increase in the detection of thyroid nodules compared to the previous rate. Many patients with thyroid disorders have been “enemies” of iodine-containing foods since they became ill, but this is actually a misconception. In fact, this is a misconception. Except for hyperthyroidism, which requires appropriate restriction of foods with high iodine content in the early stage, patients can eat in moderation when their condition improves, and there is no need to abstain from eating. Hypothyroidism patients also do not need to abstain from seafood and do not need to replace iodized salt with non-iodized salt, because iodine deficiency may also produce hypoenergetic disorders. Patients with goiter and nodules can also consume iodine-containing foods appropriately. In fact, too much iodine and too little iodine can cause thyroid disorders. Thyroid nodules, adenomas and inflammatory thyroid conditions do not require a strict restriction of iodine intake. Both healthy people and patients with thyroid disease should maintain a rational attitude towards iodine, i.e. no need to avoid iodine, but not to be high in iodine either. 150 micrograms of iodine per day is the healthy choice.