To protect thyroid health, one more "iodine" and one less "iodine" will not work!

*Only for medical professionals to read and reference Abandon one-size-fits-all, prevent the resurgence of one less "iodine", avoid one more "iodine" is too much, and protect the thyroid health of the people
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This article summarizes the history: from a country with iodine deficiency to salt iodization Status: Eliminate iodine deficiency and avoid iodine excess Future: abandon one-size-fits-all, take care of the thyroid 1 History: From a country with iodine deficiency to iodizing salt But now it has entered the ranks of iodine-sufficient countries
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In order to take off the big hat of iodine deficiency, China's iodine supplement policy has contributed greatly
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The prevention and control of iodine deficiency disorders in China is mainly divided into three stages, including iodine deficiency disease investigation, iodine supplementation in iodine-deficient areas, and iodization of salt for all people
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 Figure 1 China is now an iodine-sufficient country.
Prior to 1979, the main focus of work was to investigate the prevalence of iodine deficiency disorders in China
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According to statistics from the National Department of Iodine Deficiency Disease Prevention and Control, among the less than 1 billion Chinese people at that time, the number of people suffering from iodine deficiency disorders in China was as high as 370 million; the number of endemic goiter patients was as high as 37 million; cretinism There are 250,000 patients
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 Therefore, between 1979 and 1995, China began to implement iodine supplementation in major iodine-deficient areas, and in 1995 began to implement a general salt iodization policy, with the aim of eliminating iodine deficiency diseases
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After more than 20 years of efforts, China is the first in the world to achieve the goal of eliminating iodine deficiency disorders
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 Figure 2 Countries/regions where salt iodization is currently implemented globally However, there are concerns that iodized salt can lead to excessive iodine intake, as high iodine levels can increase the risk of certain thyroid diseases
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In fact, China has adjusted the iodized concentration of table salt twice to ensure that the consumption of iodized salt will not lead to excessive iodine
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In 2002, the iodized concentration of table salt was adjusted to 35±15mg/kg
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In 2011, this standard was lowered to the level of 20-30 mg/kg, and each provincial administrative region was allowed to decide the local salt iodization concentration according to the natural conditions of the iodine resources in the region
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 The iodization of table salt originated from the state of iodine deficiency in China at that time, and the adjustment of the iodized concentration of table salt naturally requires the support of epidemiological data
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In December 2021, Thyroid, an authoritative international journal in the field of thyroid, published an epidemiological study covering 31 provinces, autonomous regions and municipalities in China, evaluating the iodine nutritional status of Chinese people after 20 years of salt iodization and reflecting the iodine nutritional status.
One of the indicators - the prevalence of goiter characteristics
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 2 Status quo: Eliminate iodine deficiency and avoid iodine excess In 2014, the Status Quo of Iodine Nutrition and Thyroid Diseases of Chinese Residents (TIDE) was officially launched
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Led by Professor Teng Weiping and Professor Shan Zhongyan from the First Affiliated Hospital of China Medical University and the Institute of Endocrinology of China Medical University, a multi-stage cluster sampling survey of nearly 80,000 participants was completed in 31 provinces, autonomous regions and municipalities across the country in two years.
Work, obtained the iodine nutritional status and characteristics of Chinese people after 20 years of iodization of Chinese salt
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Figure 3 Findings published in the journal Thyroid This study measured participants' urinary iodine concentration (UIC), using the population's median urinary iodine concentration (MUI) as a measure of the population's iodine nutritional status
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According to the latest recommendations of WHO and the iodine global network, the iodine nutrition level is divided: MUI≥300 μg/L is iodine excess, 100-299 μg/L is suitable for iodine, and <100 μg/L is iodine deficiency
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In the iodine-deficient population, the degree of deficiency was further subdivided according to the median urinary iodine, ranging from 50-99 μg/L for mild iodine deficiency, 20-49 μg/L for moderate iodine deficiency, and <20 μg/L for severe iodine deficiency Iodine deficiency
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 Figure 4 The results of the median urinary iodine before and after the implementation of the national salt iodization policy in China showed that the MUI of adults was 177.
89 μg/L (IQR 117.
89-263.
90 μg/L), and the MUI of school-age children was 199.
75 μg/L (IQR 128.
41- 303.
37 μg/L), indicating that the Chinese are in a state of sufficient iodine
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According to the analysis of 31 provinces, there are no iodine-deficient provinces in the adult population (27 provinces have sufficient iodine intake and 4 provinces have excessive iodine intake); there are also no iodine-deficient provinces in school-age children (30 provinces).
Sufficient iodine intake, excessive iodine intake in 1 province)
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 Although there are no provinces with iodine deficiency in terms of regions, from the perspective of population, the proportion of people with excess iodine is 18.
74%, the proportion of iodine suitable is 63.
44%, and the iodine deficiency is 17.
82%
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In the iodine deficient population, the proportions of mild, severe and moderate deficiency were 13.
97%, 3.
43% and 0.
42%, respectively
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The prevalence of goiter is one of the important indicators to measure iodine nutrition.
At present, the prevalence of goiter in China is 1.
17%, which is the lowest level since the survey.
It also proves that Chinese residents have eliminated iodine deficiency (the prevalence of goiter).
rate <5%)
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 In addition, the research team of Professor Teng and Professor Shan also analyzed the relationship between different iodine nutritional status and various thyroid diseases, as well as the positive rates of thyroid peroxidase antibody (TPOAb) and thyroglobulin antibody (TgAb) using the data from the national epidemiological survey.
relationship
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Based on an iodine-appropriate population, iodine deficiency was associated with an increased risk of clinical hyperthyroidism, Graves disease, clinical hypothyroidism, thyroid autoantibody-positive, TPOAb-positive, TgAb-positive, goiter, and thyroid nodules
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These data use facts to tell people that iodine is really indispensable
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 Of course, the state of iodine excess, which is of the greatest concern, was also evaluated
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The results showed that the risk of clinical hyperthyroidism (OR 2.
05, 95%CI 1.
59-2.
63) and subclinical hypothyroidism (OR 1.
37, 95%CI 1.
22-1.
55) in the iodine-excessive population was based on the appropriate iodine population.
increased risk of thyroid nodules in people with iodine overdose actually had a lower risk (OR 0.
74, 95%CI 0.
65-0.
85)
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 3 Future: Abandon one-size-fits-all, take care of the thyroid The survey shows that the current coverage rate of iodized salt in China is 95.
37%
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The MUI of the iodized salt group was 179.
99 μg/L (IQR 120.
00-267.
00 μg/L), which was significantly higher than that of the non-iodized salt group of 136.
92 μg/L (IQR 87.
60-204.
93 μg/L)
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 The overall prevalence of goiter was 1.
17% in adults and 3.
50% in school-aged children
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There was no significant difference in the prevalence of goiter between people who consumed iodized and non-iodized salt
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However, the prevalence of goiter in the UIC<100 μg/L group (1.
68%) was higher than that in the iodine-replete group (1.
13%)
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Therefore, iodized salt supplementation may still be necessary for people with iodine deficiency
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 However, changes in the prevalence of other thyroid disorders have varied
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Since 1999, the prevalence of clinical hyperthyroidism, subclinical hyperthyroidism, and clinical hypothyroidism has gradually decreased; the positive rate of thyroid autoantibodies including TPOAb and TgAb has not changed significantly, suggesting that the prevalence of autoimmune thyroiditis has not changed significantly.
; The prevalence of subclinical hypothyroidism and thyroid nodules is increasing year by year, which has become the main reason why people are afraid of salt iodization
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 In the early stage of the implementation of national salt iodization, a transient increase in the incidence of hyperthyroidism was indeed found.
However, with the continuation of salt iodization, especially after the concentration of salt iodization was adjusted, the prevalence of major thyroid diseases gradually decreased.
, back to the previous level
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This may be the result of self-adaptation, and transient thyroid abnormalities caused by iodine supplementation usually resolve
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In addition, the positive rate of thyroid autoantibodies did not change significantly before and after salt iodization
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 Figure 5 After salt iodization, the positive rate of thyroid antibodies did not increase.
The increase in the prevalence of thyroid nodules may not be caused by salt iodization
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In fact, higher UIC levels were actually associated with a lower risk of developing thyroid nodules
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The main reasons for the increasing number of thyroid nodules around you may be the increase in the screening rate of thyroid B-ultrasound and the improvement of the resolution of B-ultrasound equipment.
In addition, factors such as increased body mass index, the existence of metabolic syndrome, and not eating iodized salt are all causes of thyroid nodules.
risk factors for disease
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 Figure 6 Too much iodine, in fact, the risk of thyroid nodules is relatively low Research believes that the current policy of maintaining MUI at the level of 100-300 μg/L is the safe dose range of iodine supplementation for the general population
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At the same time, iodine supplementation can not only treat iodine deficiency disorders, but also a necessary measure to reduce the prevalence of various thyroid diseases
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In order to protect your thyroid, one more "iodine" and one less "iodine" will not work, but we need to know that the thyroid function damage caused by iodine deficiency is often more serious
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 In general areas, 20% to 30% of the iodine in the human body comes from food, and 70% to 80% comes from iodized salt
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Iodine deficiency exists in the environment in most parts of China, and if the iodization of table salt is not adhered to, iodine deficiency may return
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Of course, if you live in an area with high levels of iodine in the water, you can choose non-iodized table salt
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Residents living in coastal areas, if the daily intake of iodine-rich foods can meet the daily iodine nutritional needs (daily iodine intake of 150 micrograms), then choose non-iodized salt is also understandable
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In addition, if there is a specific thyroid disease, there is a special need for non-iodized salt, which is now more easily available
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 Audit expert Professor Shan Zhongyan Chief Physician, Second-level Professor, Doctoral Supervisor Director of Endocrinology Department of the First Affiliated Hospital of China Medical University The National New Century Hundreds of Thousands of Talents Project National-level candidates National health and family planning outstanding contributions to young and middle-aged experts enjoy special allowances from the State Council Research direction: thyroid disease, metabolic syndrome References: [1] Li M, Eastman CJ.
The changing epidemiology of iodine deficiency .
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Global epidemiology of hyperthyroidism and hypothyroidism.
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Adhere to adding iodine to salt to protect thyroid health.
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The Characteristics of Iodine Nutrition Status in China After 20 Years of Universal Salt Iodization: An Epidemiology Study Covering 31 Provinces.
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