The thyroid gland is an important endocrine organ in the neck of the body, which secretes mainly thyroid hormones, as well as calcitonin. Iodine is an important raw material for the synthesis of thyroid hormones, and iodine deficiency can cause some thyroid disorders, while excessive iodine intake can also trigger thyroid disorders. The thyroid gland itself can suffer from a variety of diseases, and diseases of other body systems can also affect the function of the thyroid gland, so it is not strict to say in general that patients with thyroid disease should or should not take iodine supplements. Universal salt iodization is an effective measure to prevent and treat iodine deficiency disorders, and USI has been implemented in China since 1995. After the implementation of USI, the quality of China’s population has improved greatly with the gradual improvement of iodine nutrition, and the average IQ level of the whole population was 96.9 in 2005 after salt iodization, which was significantly higher than that in 1997. In 1999, WHO announced that 15 countries worldwide, including China, were the first to achieve the goal of eliminating iodine deficiency disorders. As a result, the Ministry of Health lowered the iodization level of salt in 2000, and the national iodine deficiency monitoring results in 2002 reported that the MUI of the population decreased to 241.2 μg/L, which was in the range of iodine excess. The national iodine deficiency monitoring results in 2005 showed that the MUI was 246 μg/L, with little change from 2002. There are still 5 provinces with MUI over 300μg/L, and the prevalence of goiter is 4.0% nationwide. The effectiveness of USI as an intervention to correct iodine deficiency disorders (IDD) is positive, and from a public health and socio-economic point of view, the benefits of iodine supplementation are enormous despite its low cost. However, some problems have emerged after salt iodization that cannot be ignored. In 2001, the World Health Organization, the United Nations International Children’s Fund, and the International Council for the Control of Iodine Deficiency Disorders (ICDD) proposed for the first time the definitions and dose ranges for human iodine intake of sufficient, super-sufficient, and excessive iodine intake, i.e., median urinary iodine (MUI) 100-199 μg/L is sufficient iodine intake, MUI 200-300 μg/L is super-sufficient iodine intake, and MUI >300 μg/L is excessive iodine intake. excess. According to this standard, our population has been in iodine excess and excess iodine intake since 1997. The iodized salt has caused an increase in the incidence of thyroid disease and a corresponding change in the spectrum of thyroid disease, and some people have begun to complain and become suspicious of USI. The regulations do state that salt iodization is not required in areas with high iodine levels, and many local salt companies sell iodized salt across the board. in 2008, the rate of iodine-free salt in Beijing was only 25%. Currently, according to the 2009 National Salt Iodization Monitoring Brief, there is a mixture of high iodine, iodine deficient and moderately iodized villages, which makes it difficult to regulate the whole country. The one-size-fits-all policy of salt iodization in China needs to be adjusted appropriately. Mandatory iodine supplementation has been abolished in the high water iodine area of Heze, Shandong. The population of fishermen with a daily intake of 750 grams of sea fish also does not need iodine supplementation. Patients with hyperthyroidism and Hashimoto’s disease cannot take iodized salt. Prof. Teng Weiping (head of the Chinese Endocrinology Group) pointed out that China is currently in a period of high prevalence of thyroid disease. Since 2000, there has been a gradual increase in the number of thyroid patients, especially in coastal areas such as Hangzhou, Ningbo and Zhoushan in Zhejiang Province. A survey conducted in 2010 in Zhoushan, Zhejiang Province, using high-frequency ultrasound, showed that the prevalence of thyroid nodules was 25.19%, 25.15%, 32.10%, 16.10%, and 16.17% among urban residents, farmers, salt people, fishermen, and monks in Putuo Mountain, respectively. The prevalence of thyroid nodules was 25.19%, 25.15%, 32.10%, 16.10% and 16.17%, respectively, higher than that of 10.12% and 10.18% in inland areas with moderate and high iodine. The results of a survey of monks in Putuo Mountain showed that the difference in the prevalence of thyroid nodules between monks and nuns was not statistically significant, which may be greatly related to the fact that nuns have never been pregnant and their estrogen levels have not changed significantly. In 2010, Xiao Bangzhong et al. reported a comparative analysis of the incidence of population hyperthyroidism in Yongchuan, Chongqing, where urinary iodine levels are high, and in Fuling, where urinary iodine levels are relatively low. (The prevalence of hyperthyroidism in the population increased from 4.55/100,000 before the USI in 1996 to 12.19/100,000 in 1997, an increase of 1.68 times. The prevalence of hyperthyroidism was positively correlated with iodized salt coverage and urinary iodine level. A five-year prospective study of thyroid disease in 3,761 residents in three areas with different iodine intakes was initiated by the China Medical University in 1999, and a follow-up survey was conducted in 2004. During the 5-year follow-up period, the cumulative incidence of subclinical hypothyroidism was significantly higher in Changwu, an area with excess iodine, and in Huanghua, an area with excess iodine, than in Panshan, a mildly iodine-deficient area, by a factor of 11.3 and 12.6, respectively. The cumulative incidence of autoimmune thyroiditis in Changwu and Huanghua was also significantly higher than that in Panshan, 4.4 and 5.5 times higher than that in Panshan, respectively. Iodine and thyroid cancer: It is generally believed that there is no significant difference in the incidence of thyroid cancer between iodine-sufficient and iodine-deficient areas, but the type of thyroid cancer is different between the two. Domestic Professor Teng Weiping: The relationship between excess iodine and thyroid cancer is still inconclusive. It is clear that iodine excess can lead to an increased incidence of papillary thyroid cancer, but has little effect on the overall incidence of thyroid cancer. Epidemiological survey of thyroid disease in ten cities in China: To investigate the prevalence of thyroid disease and iodine nutritional status of a sample of urban residents in China and to analyze the relationship between the prevalence of thyroid disease and iodine nutritional status. Subjects and methods:Ten cities in Beijing, Chengdu, Guangzhou, Guiyang, Jinan, Nanjing, Shanghai, Shenyang, Wuhan, and Xi’an participated in this survey, and 15,181 urban community residents (≥20 years old) were surveyed. Results: Median urinary iodine (MUI) was 228, 282, 207 and 241 μg/L in four cities, Guiyang, Nanjing, Wuhan and Xi’an, respectively, which were in the state of iodine excess, while MUI was 156, 184, 174, 185, 169 and 169 μg/L in six cities, Beijing, Chengdu, Guangzhou, Jinan, Shanghai and Shenyang, respectively, which were in the state of iodine sufficiency. The total prevalence of various thyroid diseases in the ten cities were 1.1% for clinical hyperthyroidism, 2.6% for subclinical hyperthyroidism, 0.9% for clinical hypothyroidism, 5.6% for subclinical hypothyroidism, 11.6% for TPOAb positivity, 12.6% for TgAb positivity, 2.4% for goiter, 11.6% for solitary thyroid nodules, and 7% for multiple thyroid nodules. The prevalence of clinical hyperthyroidism was 1.2% and 1.0% in iodine-sufficient areas compared with iodine-sufficient areas. The prevalence of subclinical hyperthyroidism was 1.6% and 3.2%, respectively; the prevalence of clinical hypothyroidism was 2.1% and 0.8%, respectively. The prevalence of subclinical hypothyroidism was 8.2% and 3.8%, respectively. The prevalence of goiter was 1.3% and 4.5%, respectively. The above results show that the prevalence of clinical hypothyroidism, subclinical hypothyroidism, TPOAb and TgAb positive rates are higher in iodine-sufficient areas than in iodine-sufficient areas; while the prevalence of goiter, solitary thyroid nodules and multiple nodules, and subclinical hyperthyroidism are lower in iodine-sufficient areas than in iodine-sufficient areas. (Note: In the national iodine deficiency disease surveillance, urine iodine concentration is generally measured directly by collecting a random urine sample to evaluate the iodine nutrition status of the population). On September 3, 2009, the Endocrinology Branch of the Chinese Medical Association issued a statement in response to questions from all sectors of society and the media about the “universal salt iodization” regulation: Iodine deficiency disease is a common endemic disease that endangers the health of the Chinese people and is directly related to the intellectual quality of the Chinese nation. Salt iodization is currently the best internationally recognized method of iodine supplementation and should be adhered to. The statement recommends that the state should implement the iodine supplementation policy of “scientific iodine supplementation, categorical guidance, local adaptation, no more and no less”. The USI policy should be revised and a differentiated iodine supplementation policy should be implemented in iodine deficient areas. The policy of iodine supplementation in each province, municipality and autonomous region is based on local conditions. Provinces, municipalities and autonomous regions should also further study the differences in natural iodine resources in their regions on a city and county basis, and refine their iodine supplementation policies. In areas with high iodine and sufficient iodine, stop supplying iodized salt; in areas with iodine deficiency, implement iodine supplementation in a differentiated manner, so as to make up for the lack of how much. In short, iodine supplementation should be designed according to the classification of each place and person. The iodized salt concentration should be differentiated according to the natural iodine status and dietary habits of each region; the supply of iodized salt in iodine-sufficient and iodine-high areas should be stopped, and the iodine nutritional status of residents should be continuously maintained within a safe range; individualized monitoring of urinary iodine should be strengthened for people with thyroid autoimmune genetic background and potential autoimmune thyroiditis, so as to prevent further damage to thyroid function from excessive and super-sufficient iodine. It is believed that only by combining USI with the actual situation can a new breakthrough in the prevention of thyroid disease with iodized salt be expected.