Iodine is an essential trace element for the human body and an important raw material for the synthesis of thyroid hormones. Thyroid hormone is a hormone that maintains basic bodily activities, promotes human growth and development, participates in brain development, and regulates metabolism. Therefore, sufficient iodine can ensure the synthesis of thyroid hormones and maintain the health of the body. Insufficient iodine can lead to insufficient synthesis of thyroid hormones, which cannot maintain normal physiological functions of the human body, and may even cause hypothyroidism (hypothyroidism). Adults may experience symptoms such as memory loss, constipation, weight gain, dry and rough skin, as well as slow reactions and drowsiness. Severe cases can affect normal life and work. Iodine deficiency disorder is a disease caused by insufficient iodine intake in the body, mainly including endemic goiter and endemic cretinism. Localized goiter, commonly known as "big neck", can compress the human trachea and esophagus in severe cases, leading to difficulty breathing and swallowing. Iodine deficiency has different effects on different populations. Iodine deficiency in children can lead to thyroid hormone deficiency, directly affecting intellectual and physical development, and even causing the inability to take care of oneself. Pregnant women have a very high demand for iodine in the early stages of pregnancy, and iodine deficiency can directly affect the development of the fetal nervous system. If pregnant women suffer from severe iodine deficiency, it may lead to endemic cretinism in the fetus, seriously affecting intelligence and growth and development, and even causing miscarriage, premature birth, etc. So for pregnant women, iodine intake is generally significantly higher than that of normal adults. According to the geographical characteristics of our country, residents should consume iodized salt to meet their daily iodine intake needs. For pregnant and lactating women, it is encouraged to consume salt from pregnant women with high iodine content, or to consume more seafood, including kelp, seaweed, etc. For infants and young children who are breastfed, special attention should be paid to whether the mother's iodine intake is sufficient. For infants and young children who are not breastfed, parents should consider the origin of the formula when purchasing it. In order to prevent and treat iodine deficiency disorders, China stipulates that iodine must be added to infant formula. If parents choose imported milk powder, they should pay attention to the iodine content. For patients with hyperthyroidism, strict control of iodine intake is necessary, and currently it is recommended to consume non iodized salt. Iodine supplementation is usually not recommended during hyperthyroidism. Do people with thyroid nodules need iodine supplementation? It depends on whether the formation of thyroid nodules is related to iodine intake. For example, when severe iodine deficiency causes thyroid hyperplasia, it can also lead to the formation of thyroid nodules. In this case, iodine supplementation can have a certain degree of improvement, but in severe cases, other treatment plans also need to be combined. So people with thyroid nodules need to go to the hospital for medical treatment, and specifically analyze the relationship between nodules and iodine intake. At present, no direct relationship has been found between iodine supplementation and thyroid cancer. Thyroid enlargement does not necessarily mean iodine deficiency, there are many reasons that can lead to thyroid enlargement. When the human body is severely deficient in iodine, it may cause thyroid enlargement. In this case, patients can consult an endocrinologist to determine whether thyroid enlargement is caused by iodine deficiency. Some thyroid enlargement may be a surgical problem and can be treated with thyroid surgery or basic surgery. If iodine deficiency disease is detected in the early stages and the body supplements iodine in a timely manner, there will be no major harm. After recovering from iodine deficiency disorders, it is important to adhere to iodine supplementation to prevent recurrence. Generally speaking, the adequacy of iodine intake can be determined by testing urine iodine, but it is not recommended to test urine iodine for individuals with normal thyroid function and normal consumption of iodized salt. For pregnant women, it is necessary to test for urinary iodine, and they can adjust their diet based on the test results. (New Press) (The author is the chief physician of the Endocrinology Department at Peking Union Medical College Hospital)