Iodine and the thyroid gland are closely related, and the thyroid gland absorbs iodine to synthesize thyroid hormones. Iodine deficiency can cause low thyroid hormone and turn into hypothyroidism. Patients with hypothyroidism can have low basal metabolism, making the body feel weak and cold, and in severe cases, mucinous edema can occur, and fetuses, infants and adolescents can have delayed brain development, causing “cretinism”. However, excessive iodine intake does increase the risk of hyperthyroidism. The correlation between the amount of iodine and the development of thyroid tumors needs to be further investigated. International studies on iodine have shown that the relationship between iodine intake and thyroid disease is U-shaped, with both high and low iodine intake leading to an increase in thyroid disease. When there is an excess of iodine, the thyroid gland regulates itself to be insensitive to iodine and the excess iodine is excreted in the urine. After a period of time, even if a normal amount of iodine is consumed, the thyroid gland cannot absorb iodine and cannot synthesize thyroid hormones. The thyroid gland then regulates itself to a “hypersensitive” state and becomes hyperfunctional, and after a long period of excitement, the thyroid gland becomes overstretched and swollen. Similarly, when the amount of iodine is not enough, the thyroid gland becomes directly hypersensitive and works very hard, which makes it prone to problems over time. Therefore, the amount of iodine intake or whether to choose iodized salt should start from yourself, so that it is different and reasonable for each person, and avoid the two extremes of no iodine intake at all and large amount of iodine intake. For people in coastal areas who usually consume more iodine-rich foods such as seafood and nori or people with hyperthyroidism, they can choose non-iodized salt, while for normal people without hyperthyroidism, they should not reject iodized salt. Theoretically, to see if your iodine intake is more or less, check your urinary iodine. The amount of iodine needed by the average person’s body is 150-200 micrograms per day, and more than 300 micrograms is too much.