Since iodine deficiency disorders are caused by environmental iodine deficiency, only by continuously ensuring the consumption of iodized salt can iodine deficiency disorders be eliminated on a sustainable basis, which means that salt iodization for all people is a long-term activity. However, medical studies have also confirmed that some patients with thyroid disorders should be careful with iodized salt. In fact, a proper understanding of iodized salt is necessary. Iodine is an essential trace element for the human body and is one of the raw materials for the synthesis of thyroid hormones. Insufficient iodine intake can lead to thyroid follicular hyperplasia and increase the chance of goiter or nodules, and conversely, excessive intake can lead to thyroid diseases such as thyroiditis or thyroid cancer. Therefore, the intake of iodine cannot be generalized or answered in a broad-brush manner. Based on the iodization of salt in China at 35 micrograms/gram and a per capita salt intake of 10 grams per day, our daily intake of iodine is 350 micrograms, which is not higher than the recommended amount by the World Health Organization after deducting the loss from cooking and human metabolism. Even if we consider the differences between the European and American races and the Chinese physique and moderately lower the standard, the current daily iodine intake in China is still within the acceptable range. Then residents of coastal cities like Shanghai, especially those who usually consume more seafood, have sufficient iodine intake, then there is no need to supplement it by iodized salt, especially for patients with thyroid nodules. However, if you eat less iodine, you are going from one extreme to the other. According to relevant studies, the incidence of thyroid cancer is significantly higher in both iodine-deficient and high-iodine areas than in areas with normal iodine. The level of iodine intake and the type of thyroid cancer pathology correlate, with high incidence of follicular carcinoma in iodine-deficient areas and papillary carcinoma in iodine-sufficient areas. Therefore, we recommend scientific iodine supplementation. The simpler way is that those who often eat seafood should eat less iodized salt to avoid excessive iodine intake; those who do not eat seafood should not exclusively eat non-iodized salt to avoid insufficient iodine intake. Second, which patients are not suitable for iodized salt? 1, hyperthyroidism (referred to as “hyperthyroidism”) Hyperthyroidism is a series of hypermetabolic syndrome caused by high levels of thyroid hormones in the body, iodine is the raw material for synthesizing thyroid hormones, consumption of iodized salt or food containing iodine is equal to a constant supply of raw materials for synthesizing thyroid hormones. Therefore, even taking anti-thyroid drugs cannot effectively control the condition. Therefore, patients with hyperthyroidism should be cautious in consuming iodized salt and food containing iodine. 2, chronic lymphatic thyroiditis (also known as “Hashimoto’s disease”) Hashimoto’s disease is a chronic autoimmune disease, mostly seen in women aged 30 to 50 years old, clinical manifestations of painless diffuse enlargement of the thyroid gland, more than half will cause hypothyroidism. Iodine intake is an important environmental factor influencing the development of the disease. It has been found that a high concentration of iodine environment induces damage to the thyroid’s own tissues and accelerates apoptosis of thyroid cells. Therefore, patients with Hashimoto’s disease should have an iodine-restricted diet. 3, Goiter in non-iodine-deficient areas Iodine deficiency can cause goiter, and similarly, excess iodine can also cause goiter. Drugs containing large amounts of iodine can also cause goiter, such as compound iodine solution, amiodarone, herbal kombucha, seaweed, etc. If a goiter is found in a non-iodine-deficient area, it should be considered to be caused by excess iodine and patients should not be blindly allowed to supplement iodine. 4 . Thyroid cancer High iodine diet can promote the development of thyroid cancer. Environmental factors (iodine deficiency or high iodine) may be an important factor affecting the development of thyroid cancer and play an important role in the process of thyroid cancer. It is currently believed that both chronic iodine deficiency and chronic high iodine intake can lead to overproduction of thyrotropic hormones by the pituitary gland and contribute to the development of goiter, which is one of the risk factors for thyroid cancer, especially in female patients. Only a reasonable intake of iodine according to different conditions can better prevent and treat various thyroid diseases.