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<front>
<journal-meta>
<journal-id journal-id-type="publisher-id">Front. Endocrinol.</journal-id>
<journal-title>Frontiers in Endocrinology</journal-title>
<abbrev-journal-title abbrev-type="pubmed">Front. Endocrinol.</abbrev-journal-title>
<issn pub-type="epub">1664-2392</issn>
<publisher>
<publisher-name>Frontiers Media S.A.</publisher-name>
</publisher>
</journal-meta>
<article-meta>
<article-id pub-id-type="doi">10.3389/fendo.2023.1234482</article-id>
<article-categories>
<subj-group subj-group-type="heading">
<subject>Endocrinology</subject>
<subj-group>
<subject>Original Research</subject>
</subj-group>
</subj-group>
</article-categories>
<title-group>
<article-title>Relation between iodine nutrition and thyroid diseases in Qinghai, China</article-title>
</title-group>
<contrib-group>
<contrib contrib-type="author">
<name>
<surname>Fan</surname><given-names>Xiaoxia</given-names>
</name>
<xref ref-type="aff" rid="aff1"><sup>1</sup></xref>
<xref ref-type="aff" rid="aff2"><sup>2</sup></xref>
<xref ref-type="aff" rid="aff3"><sup>3</sup></xref>
<xref ref-type="author-notes" rid="fn002"><sup>&#x2020;</sup></xref>
<uri xlink:href="https://loop.frontiersin.org/people/2252964"/>
</contrib>
<contrib contrib-type="author">
<name>
<surname>Zhao</surname><given-names>Lingling</given-names>
</name>
<xref ref-type="aff" rid="aff1"><sup>1</sup></xref>
<xref ref-type="author-notes" rid="fn002"><sup>&#x2020;</sup></xref>
</contrib>
<contrib contrib-type="author">
<name>
<surname>Wang</surname><given-names>Shuqiong</given-names>
</name>
<xref ref-type="aff" rid="aff1"><sup>1</sup></xref>
</contrib>
<contrib contrib-type="author">
<name>
<surname>Song</surname><given-names>Kang</given-names>
</name>
<xref ref-type="aff" rid="aff1"><sup>1</sup></xref>
</contrib>
<contrib contrib-type="author">
<name>
<surname>Wang</surname><given-names>Beibei</given-names>
</name>
<xref ref-type="aff" rid="aff1"><sup>1</sup></xref>
</contrib>
<contrib contrib-type="author">
<name>
<surname>Xie</surname><given-names>Yanling</given-names>
</name>
<xref ref-type="aff" rid="aff1"><sup>1</sup></xref>
</contrib>
<contrib contrib-type="author">
<name>
<surname>Jiang</surname><given-names>Yanping</given-names>
</name>
<xref ref-type="aff" rid="aff1"><sup>1</sup></xref>
</contrib>
<contrib contrib-type="author">
<name>
<surname>Lin</surname><given-names>Lijun</given-names>
</name>
<xref ref-type="aff" rid="aff1"><sup>1</sup></xref>
</contrib>
<contrib contrib-type="author" corresp="yes">
<name>
<surname>Teng</surname><given-names>Weiping</given-names>
</name>
<xref ref-type="aff" rid="aff4"><sup>4</sup></xref>
<xref ref-type="author-notes" rid="fn001"><sup>*</sup></xref>
<xref ref-type="author-notes" rid="fn002"><sup>&#x2020;</sup></xref>
<uri xlink:href="https://loop.frontiersin.org/people/708804"/>
</contrib>
<contrib contrib-type="author" corresp="yes">
<name>
<surname>Cai</surname><given-names>Chunmei</given-names>
</name>
<xref ref-type="aff" rid="aff2"><sup>2</sup></xref>
<xref ref-type="aff" rid="aff3"><sup>3</sup></xref>
<xref ref-type="author-notes" rid="fn001"><sup>*</sup></xref>
<xref ref-type="author-notes" rid="fn002"><sup>&#x2020;</sup></xref>
<uri xlink:href="https://loop.frontiersin.org/people/1098143"/>
</contrib>
<contrib contrib-type="author" corresp="yes">
<name>
<surname>Yao</surname><given-names>Yongli</given-names>
</name>
<xref ref-type="aff" rid="aff1"><sup>1</sup></xref>
<xref ref-type="author-notes" rid="fn001"><sup>*</sup></xref>
<xref ref-type="author-notes" rid="fn002"><sup>&#x2020;</sup></xref>
</contrib>
</contrib-group>
<aff id="aff1"><sup>1</sup><institution>Department of Endocrinology, Qinghai Provincial People&#x2019;s Hospital</institution>, <addr-line>Xining</addr-line>, <country>China</country></aff>
<aff id="aff2"><sup>2</sup><institution>Key Laboratory of Ministry of Education for High Altitude Medicine, Research Center for High Altitude Medicine</institution>, <addr-line>Xining</addr-line>, <country>China</country></aff>
<aff id="aff3"><sup>3</sup><institution>Key Laboratory of Application and Foundation for High Altitude Medicine Research in Qinghai Province (Qinghai&#x2212;Utah Joint Research Key Lab for High Altitude Medicine) Qinghai University</institution>, <addr-line>Xining</addr-line>, <country>China</country></aff>
<aff id="aff4"><sup>4</sup><institution>Department of Endocrinology and Metabolism, Institute of Endocrinology, The First Affiliated Hospital of China Medical University</institution>, <addr-line>Shenyang</addr-line>, <country>China</country></aff>
<author-notes>
<fn fn-type="edited-by">
<p>Edited by: Joseph V. Martin, Rutgers University Camden, United States</p>
</fn>
<fn fn-type="edited-by">
<p>Reviewed by: Chukwuma Okoye, University of Pisa, Italy; Eleonore Fr&#xf6;hlich, Medical University of Graz, Austria; Juan C. Solis-Sainz, Autonomous University of Queretaro, Mexico</p>
</fn>
<fn fn-type="corresp" id="fn001">
<p>*Correspondence: Yongli Yao, <email xlink:href="mailto:yaoylqh@126.com">yaoylqh@126.com</email>; Chunmei Cai, <email xlink:href="mailto:caicm@qhu.edu.cn">caicm@qhu.edu.cn</email>; Weiping Teng, <email xlink:href="mailto:twp@vip.163.com">twp@vip.163.com</email>
</p>
</fn>
<fn fn-type="equal" id="fn002">
<p>&#x2020;These authors have contributed equally to this work</p>
</fn>
</author-notes>
<pub-date pub-type="epub">
<day>08</day>
<month>09</month>
<year>2023</year>
</pub-date>
<pub-date pub-type="collection">
<year>2023</year>
</pub-date>
<volume>14</volume>
<elocation-id>1234482</elocation-id>
<history>
<date date-type="received">
<day>04</day>
<month>06</month>
<year>2023</year>
</date>
<date date-type="accepted">
<day>18</day>
<month>08</month>
<year>2023</year>
</date>
</history>
<permissions>
<copyright-statement>Copyright &#xa9; 2023 Fan, Zhao, Wang, Song, Wang, Xie, Jiang, Lin, Teng, Cai and Yao</copyright-statement>
<copyright-year>2023</copyright-year>
<copyright-holder>Fan, Zhao, Wang, Song, Wang, Xie, Jiang, Lin, Teng, Cai and Yao</copyright-holder>
<license xlink:href="http://creativecommons.org/licenses/by/4.0/">
<p>This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.</p>
</license>
</permissions>
<abstract>
<sec>
<title>Objective</title>
<p>To investigate the adult iodine nutrition and the prevalence of thyroid diseases in Qinghai Province, and analyze the correlation between iodine and thyroid diseases, so as to provide a basis for adjusting the salt iodization plan in Qinghai Province.</p>
</sec>
<sec>
<title>Methods</title>
<p>Using cluster and stratified sampling method to select 2628 permanent residents over 18 years old in Qinghai Province for questionnaire survey, physical examination, thyroid color ultrasound, and laboratory index detection.</p>
</sec>
<sec>
<title>Results</title>
<p>1. The coverage of iodized salt in adults is 99.71%. 2. The detection rates of thyroid disorders in adults were as follows: Clinical hyperthyroidism was 1.20%, subclinical hyperthyroidism was 0.20%, clinical hypothyroidism was 1.00%, subclinical hypothyroidism was 29.20%, and the goiter was 2.10%. The percentages positivity of TPO Ab, TG Ab, goiter was 9.80%, 9.20%, 2.10%, respectively. Among them single thyroid nodule was 6.40%, multi-nodule thyroid gland was 1.80%. 3. The percentages of mild iodine deficiency, moderate iodine deficiency, Severe iodine deficiency, adequate iodine intake (AI), more than adequate iodine intake (MAI)and excessive iodine intake (EI)were 8.41%, 2.17%, 0.26%, 33.22%, 28.35%, and 27.59%, respectively. The percentages of mild, moderate and severe iodine deficiency in urban populations (7.13%, 0.87%, 0.0%) were significantly lower than those in rural populations (9.81%, 3.59%, 0.56%) (P &lt; 0.05), and the rates of adequate, more than adequate iodine intake in urban populations (36.03%, 30.93%) were significantly higher than that in rural populations (30.14%, 25.52%). The rate of excess iodine intake was higher in rural areas (30.38%) than in urban areas (25.04%). 4. The positive rates of subclinical hypothyroidism, goiter, TPO Ab and TG Ab in female adults (35.28%, 3.39%, 13.54%, 13.94%) were higher than those in male adults (23.58%, 0.96%, 6.266%, 4.79%). The detection rate of single thyroid nodules was higher in urban (8.01%) than rural populations (4.70%), while the detection rate of hypothyroidism, subclinical hypothyroidism, and goiter (0.58%, 25.84%, 1.38%) was lower than that in rural populations (1.52%, 32.96%, 2.96%) (P&lt;0.05). 5. There was no statistical significance in the detection rates of clinical hyperthyroidism, subclinical hypothyroidism, subclinical hypothyroidism, goiter, thyroid nodules, TPO Ab and TG Ab positive rates in different iodine nutritional status (P&gt;0.05). The positive rate of hypothyroidism in the iodine deficiency group is higher than in other iodine nutrition groups.</p>
</sec>
<sec>
<title>Conclusion</title>
<p>The nutritional status of iodine in Qinghai Province is iodine excess. Subclinical hypothyroidism was detected at a high rate. Subclinical hypothyroidism, goiter, TPO Ab, and TG Ab were more common in female than in male. The proportion of mild, moderate, and severe iodine deficiency was higher in urban areas than in rural areas. The detection rate of thyroid nodules was higher in urban than in rural areas, and that of hypothyroidism, subclinical hypothyroidism, and goiter was lower than that in rural populations. The detection rate of clinical hypothyroidism was statistically significant in different iodine nutritional states (P&lt; 0.05).</p>
</sec>
</abstract>
<kwd-group>
<kwd>Qinghai province</kwd>
<kwd>thyroid disease</kwd>
<kwd>iodine nutrition</kwd>
<kwd>epidemiology</kwd>
<kwd>relation</kwd>
</kwd-group>
<counts>
<fig-count count="0"/>
<table-count count="6"/>
<equation-count count="0"/>
<ref-count count="24"/>
<page-count count="8"/>
<word-count count="3890"/>
</counts>
<custom-meta-wrap>
<custom-meta>
<meta-name>section-in-acceptance</meta-name>
<meta-value>Thyroid Endocrinology</meta-value>
</custom-meta>
</custom-meta-wrap>
</article-meta>
</front>
<body>
<sec id="s1">
<label>1</label>
<title>Highlights</title>
<list list-type="bullet">
<list-item>
<p>The first large-scale investigation of the association of iodine nutritional status with thyroid disease was reported in Qinghai Province since China implemented Universal Salt Iodization (USI) legislation.</p>
</list-item>
<list-item>
<p>2650 individuals were surveyed, of whom 2628 had completed data. Iodized salt coverage in adults was 99.71%. The median urinary iodine level of the adult populations was 217.90 &#xb5;g/L.</p>
</list-item>
<list-item>
<p>The detection rates of thyroid disorders in adults were as follows: Clinical hyperthyroidism was 1.20%, subclinical hyperthyroidism was 0.20%, clinical hypothyroidism was 1.00%, subclinical hypothyroidism was 29.20%, and the goiter was 2.10%. The percentages positivity of TPO Ab, TG Ab, goiter was 9.80%, 9.20%, 2.10%, respectively. Among them single thyroid nodule was 6.40%, multi-nodule was 1.80%.</p>
</list-item>
<list-item>
<p>The percentages of mild iodine deficiency, moderate iodine deficiency, severe iodine deficiency, adequate iodine intake (AI), more than adequate iodine intake (MAI)and excessive iodine intake (EI)were 8.41%, 2.17%, 0.26%, 33.22%, 28.35%, and 27.59%, respectively. The percentages of mild, moderate and severe iodine deficiency in urban populations (7.13%, 0.87%, 0.0%) were significantly lower than those in rural populations (9.81%, 3.59%, 0.56%) (P &lt; 0.05), and the rate of adequate, more than adequate iodine intake in urban populations (36.03%, 30.93%) was significantly higher than that in rural populations (30.14%, 25.52%). The rate of excess iodine intake was higher in rural areas (30.38%) than in urban populations (25.04%).</p>
</list-item>
<list-item>
<p>The positive rates of subclinical hypothyroidism, goiter, TPO Ab and TG Ab in female adults (35.28%, 3.39%, 13.54%, 13.94%) were higher than those in male adults (23.58%, 0.96%, 6.266%, 4.79%). The detection rate of single thyroid nodules was higher in urban (8.01%) than rural populations (4.70%), while the detection rate of hypothyroidism, subclinical hypothyroidism, and goiter (0.58%, 25.84%, 1.38%) was lower than that in rural populations (1.52%, 32.96%, 2.96%).</p>
</list-item>
<list-item>
<p>No statistical significance in the detection rate of clinical hyperthyroidism, subclinical hyperthyroidism, clinical hypothyroidism, subclinical hypothyroidism, goiter, thyroid nodule, and TPO Ab positive ratio of different iodine nutrition conditions (P &gt; 0.05). The detection rate of clinical hypothyroidism was statistically significant in different iodine nutritional states (P&lt; 0.05).</p>
</list-item>
</list>
</sec>
<sec id="s2" sec-type="intro">
<label>2</label>
<title>Introduction</title>
<p>Thyroid disease is a global public health problem, and iodine nutritional status is closely related to thyroid disease (<xref ref-type="bibr" rid="B1">1</xref>). There was once a mild to moderate iodine deficiency in China until 1996, when the Universal Salt Iodization (USI) policy was implemented. In 2010, 28 provinces had eliminated iodine deficiency disorders. Iodine plays a key role in thyroid hormone synthesis and thyroid cell function. Insufficient or excessive iodine intake can cause thyroid problems (<xref ref-type="bibr" rid="B2">2</xref>). Iodine deficiency disease is one of the most serious epidemic diseases in Qinghai Province which is located in the northeastern part of the Qinghai-Tibet Plateau at an altitude of 1644&#xa0;m to 6851&#xa0;m. All 43 counties (cities, districts) in the province are severely iodine deficient areas. Through the government mandatory implemented of universal salt iodization, the coverage of iodized salt in our province has significantly improved, and the iodine nutrition status of the population has effectively improved. The national food safety standard &#x201c;Iodine Content in Edible Salt&#x201d; (GB 26878-2011) was adopted in 2012. Qinghai Province selected a salt iodization level of (30 &#xb1; 9) mg/kg according to the level of iodine nutrition of the population and the need to continuously eliminate the hazards of iodine deficiency. According to the 2016 survey, the urine iodine level of children aged 8-10 in Qinghai Province is appropriate. The TIDE program (<xref ref-type="bibr" rid="B3">3</xref>) found that Qinghai Province had changed from iodine deficiency to current iodine excess areas. However, there has been no report on the large-scale thyroid disease prevalence and associated thyroid disease relationship in Qinghai Province after USI, and the effect of iodine on the relationship with thyroid disease. This study investigated the iodine nutritional status, the changes in the prevalence and spectrum of thyroid diseases, and the impact of the relationship between iodine nutritional levels and thyroid disease in Qinghai Province, providing a scientific basis for determining the optimal iodine intake and reducing the risk of thyroid diseases for Qinghai people.</p>
</sec>
<sec id="s3" sec-type="materials|methods">
<label>3</label>
<title>Materials and methods</title>
<sec id="s3_1">
<label>3.1</label>
<title>Study participants</title>
<p>Inclusion criteria: Community residents aged&gt;18 years, permanent residents who have lived in the region for more than 5 years. Exclusion criteria: pregnancy; severe liver and kidney disease; recent use of hormone drugs (except thyroid hormone replacement therapy). All participants provided written informed consent after receiving a thorough explanation of the research procedures.</p>
</sec>
<sec id="s3_2">
<label>3.2</label>
<title>Research method</title>
<sec id="s3_2_1">
<label>3.2.1</label>
<title>Sampling method</title>
<p>Cluster sampling was used to conduct a cross-sectional survey of permanent residents over 18 years of age in Qinghai province from September 2015 to March 2016.&#xa0;A total of 2650 people were surveyed, including 2628 with complete data. The participants of each age group are shown in <xref ref-type="table" rid="T1"><bold>Table&#xa0;1</bold></xref>. Among them, there are 1374 urban residents and 1254 rural residents.</p>
<table-wrap id="T1" position="float">
<label>Table&#xa0;1</label>
<caption>
<p>Age, gender, and urban-rural structure of the survey cohort.</p>
</caption>
<table frame="hsides">
<thead>
<tr>
<th valign="top" rowspan="2" align="left">Age (years)</th>
<th valign="top" rowspan="2" align="left">Total(%)</th>
<th valign="top" colspan="2" align="left">Urban<break/>(n=1374)</th>
<th valign="top" colspan="2" align="left">Rural<break/>(n=1254)</th>
</tr>
<tr>
<th valign="top" align="left">Male</th>
<th valign="top" align="left">Female</th>
<th valign="top" align="left">Male</th>
<th valign="top" align="left">Female</th>
</tr>
</thead>
<tbody>
<tr>
<td valign="top" align="left">18-29</td>
<td valign="top" align="left">636(24.20)</td>
<td valign="top" align="left">184</td>
<td valign="top" align="left">171</td>
<td valign="top" align="left">145</td>
<td valign="top" align="left">136</td>
</tr>
<tr>
<td valign="top" align="left">30-39</td>
<td valign="top" align="left">547(20.81)</td>
<td valign="top" align="left">148</td>
<td valign="top" align="left">135</td>
<td valign="top" align="left">125</td>
<td valign="top" align="left">139</td>
</tr>
<tr>
<td valign="top" align="left">40-49</td>
<td valign="top" align="left">568(21.61)</td>
<td valign="top" align="left">157</td>
<td valign="top" align="left">142</td>
<td valign="top" align="left">135</td>
<td valign="top" align="left">134</td>
</tr>
<tr>
<td valign="top" align="left">50-59</td>
<td valign="top" align="left">424(16.13)</td>
<td valign="top" align="left">108</td>
<td valign="top" align="left">95</td>
<td valign="top" align="left">127</td>
<td valign="top" align="left">94</td>
</tr>
<tr>
<td valign="top" align="left">60-69</td>
<td valign="top" align="left">263(10.01)</td>
<td valign="top" align="left">69</td>
<td valign="top" align="left">69</td>
<td valign="top" align="left">65</td>
<td valign="top" align="left">60</td>
</tr>
<tr>
<td valign="top" align="left">&#x2265;70</td>
<td valign="top" align="left">190(7.23)</td>
<td valign="top" align="left">45</td>
<td valign="top" align="left">51</td>
<td valign="top" align="left">50</td>
<td valign="top" align="left">44</td>
</tr>
<tr>
<td valign="top" align="left">Total</td>
<td valign="top" align="left">2628(100)</td>
<td valign="top" align="left">711</td>
<td valign="top" align="left">663</td>
<td valign="top" align="left">647</td>
<td valign="top" align="left">607</td>
</tr>
</tbody>
</table>
<table-wrap-foot>
<fn>
<p>*Proportion of each age group: according to the standardized proportion of the 2010 national population census.</p>
</fn>
</table-wrap-foot>
</table-wrap>
<sec id="s3_2_1_1">
<label>3.2.1.1</label>
<title>Thyroid ultrasound examination</title>
<p>Thyroid ultrasound was performed using the US LOGIQ 100 PRO, GE, Milwaukee, Wisconsin, with a transducer probe frequency of 7.5 MHz.</p>
</sec>
<sec id="s3_2_1_2">
<label>3.2.1.2</label>
<title>Thyroid function</title>
<p>Fasting venous blood samples from all investigated residents were collected. The central laboratory in Shenyang measured FT3, FT4, TSH, TPO Ab, and TG Ab by chemiluminescence immunoassay using a Cobas 601 analyzer (Roche Diagnostics, Switzerland).</p>
</sec>
<sec id="s3_2_1_3">
<label>3.2.1.3</label>
<title>Urine iodine level detection</title>
<p>Collect the fasting urine of the subjects and use the urine sample to detect their iodine content. Urine iodine was measured by inductively coupled plasma mass spectrometry (Agilent 7700x, Agilent Technologies, USA).</p>
</sec>
</sec>
<sec id="s3_2_2">
<label>3.2.2</label>
<title>Definition of disease</title>
<p>According to the WHO/UNICEF/ICC IDD recommendations and the epidemiological study of thyroid diseases mentioned above, the classification of urinary iodine and diagnostic criteria for thyroid diseases (<xref ref-type="bibr" rid="B4">4</xref>, <xref ref-type="bibr" rid="B5">5</xref>) are shown in <xref ref-type="table" rid="T2"><bold>Table&#xa0;2</bold></xref>.</p>
<table-wrap id="T2" position="float">
<label>Table&#xa0;2</label>
<caption>
<p>Diagnostic criteria for thyroid diseases and classification criteria for urinary iodine.</p>
</caption>
<table frame="hsides">
<thead>
<tr>
<th valign="top" align="left">Thyroid disease</th>
<th valign="top" align="left">Diagnostic criteria</th>
</tr>
</thead>
<tbody>
<tr>
<td valign="top" align="left">Clinical hyperthyroidism</td>
<td valign="top" align="left">TSH&lt;0.27mIU/L;FT4&gt;22pmol/L or FT3&gt;6.8pmol/L</td>
</tr>
<tr>
<td valign="top" align="left">Subclinical hyperthyroidism (SH)</td>
<td valign="top" align="left">TSH&lt;0.27mIU/L;FT4 versus FT3 within reference range(FT4 12.0-22.0pmol/L;FT3 3.1-6.8pmol/L)</td>
</tr>
<tr>
<td valign="top" align="left">Clinical hypothyroidism</td>
<td valign="top" align="left">TSH&gt;4.2mIU/L;FT4&lt;12pmol/L</td>
</tr>
<tr>
<td valign="top" align="left">Subclinical hypothyroidism (SCH)</td>
<td valign="top" align="left">TSH&gt;4.2mIU/L;FT4 12-22pmol/L</td>
</tr>
<tr>
<td valign="top" align="left">TPO Ab positivity</td>
<td valign="top" align="left">TPO Ab&gt;34IU/ml</td>
</tr>
<tr>
<td valign="top" align="left">TG Ab positivity</td>
<td valign="top" align="left">TG Ab&gt;115IU/ml</td>
</tr>
<tr>
<td valign="top" align="left">Goiter</td>
<td valign="top" align="left">male&gt;22.5ml;female &gt;25.4ml</td>
</tr>
<tr>
<td valign="top" align="left">Thyroid nodule</td>
<td valign="top" align="left">At least one thyroid nodule in patients with non- thyroid enlargement(&gt;5mm)</td>
</tr>
<tr>
<td valign="top" align="left">deficient iodine intake (DI)</td>
<td valign="top" align="left">Median urinary iodine &lt;100&#xb5;g/L</td>
</tr>
<tr>
<td valign="top" align="left">Mild iodine deficiency</td>
<td valign="top" align="left">Median urinary iodine 50-99&#xb5;g/L</td>
</tr>
<tr>
<td valign="top" align="left">Moderate iodine deficiency</td>
<td valign="top" align="left">Median urinary iodine 20-49&#xb5;g/L</td>
</tr>
<tr>
<td valign="top" align="left">Severe iodine deficiency</td>
<td valign="top" align="left">Median urinary iodine &lt;20&#xb5;g/L</td>
</tr>
<tr>
<td valign="top" align="left">Adequate iodine intake(AI)</td>
<td valign="top" align="left">Median urinary iodine 100- &lt;200&#xb5;g/L</td>
</tr>
<tr>
<td valign="top" align="left">More than adequate iodine intake<break/>(MAI)</td>
<td valign="top" align="left">Median urinary iodine 200- &lt;300&#xb5;g/L</td>
</tr>
<tr>
<td valign="top" align="left">Excessive iodine intake(EI)</td>
<td valign="top" align="left">Median urinary iodine &#x2265;300&#xb5;g/L</td>
</tr>
</tbody>
</table>
</table-wrap>
</sec>
<sec id="s3_2_3">
<label>3.2.3</label>
<title>Diagnostic criteria</title>
<p>The normal reference value range of each index in the laboratory examination is within the normal range of the applied reagent kit.</p>
</sec>
</sec>
<sec id="s3_3">
<label>3.3</label>
<title>Statistical analysis</title>
<p>The data were statistically analyzed using SPSS26.0 software. The measurement data were represented by the median (quartile) [M (Q1, Q3)]. The comparison was carried out using the Z test and the comparison of multiple samples was carried out using the F test; X<sup>2</sup> test or Fisher&#x2019;s exact probability method was used to compare counting data; The difference was statistically significant with P&lt;0.05.</p>
</sec>
</sec>
<sec id="s4">
<label>4</label>
<title>Research results</title>
<sec id="s4_1">
<label>4.1</label>
<title>General situation of survey objects</title>
<p>A total of 2650 participants completed the study, of which 22 were excluded due to lack of gender, age, or thyroid function testing information. Therefore, we analyzed the remaining 2628, 1374 in urban areas and 1254 in rural areas, including 1358 males (51.7%) and 1270 females (48.3%), with a balanced gender composition.</p>
</sec>
<sec id="s4_2" sec-type="results">
<label>4.2</label>
<title>Results of the urine iodine test and iodized salt coverage rate in adults</title>
<p>Iodized salt is covered by 99.71% of adults (<xref ref-type="table" rid="T3"><bold>Table&#xa0;3</bold></xref>). The median population (urinary iodine, UIC) was 217.90 (148.08, 312.73) ug/L, the median UIC for male was 220.84 (153.97,315.51) ug/L and the median UIC for female was 213.87 (142.53, 310.79) ug/L. UIC did not differ significantly between adults of different sexes or ages (P&gt;0.05)</p>
<table-wrap id="T3" position="float">
<label>Table&#xa0;3</label>
<caption>
<p>Comparison of UIC among adults of different sexes and ages [M (Q1, Q3), ug/l].</p>
</caption>
<table frame="hsides">
<thead>
<tr>
<th valign="top" align="left">Variables</th>
<th valign="top" align="left">Number</th>
<th valign="top" align="left">UIC (ug/L)</th>
<th valign="top" align="left">Z/F</th>
<th valign="top" align="left"><italic>P</italic>
</th>
</tr>
</thead>
<tbody>
<tr>
<td valign="top" align="left">sex</td>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" align="left">1.34</td>
<td valign="top" align="left">0.521</td>
</tr>
<tr>
<td valign="top" align="left">&#x2003;Male</td>
<td valign="top" align="left">1358</td>
<td valign="top" align="left">220.84(153.97, 315.51)</td>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
</tr>
<tr>
<td valign="top" align="left">&#x2003;Female</td>
<td valign="top" align="left">1270</td>
<td valign="top" align="left">213.87(142.53, 310.79)</td>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
</tr>
<tr>
<td valign="top" align="left">Age/year</td>
<td valign="top" align="left"/>
<td valign="top" align="left"/>
<td valign="top" rowspan="7" align="left">1.68</td>
<td valign="top" rowspan="7" align="left">0.139</td>
</tr>
<tr>
<td valign="top" align="left">&#x2003;18-29</td>
<td valign="top" align="left">636</td>
<td valign="top" align="left">270.29(177.26, 484.92)</td>
</tr>
<tr>
<td valign="top" align="left">&#x2003;30-39</td>
<td valign="top" align="left">547</td>
<td valign="top" align="left">225.96(151.10, 312.06)</td>
</tr>
<tr>
<td valign="top" align="left">&#x2003;40-49</td>
<td valign="top" align="left">568</td>
<td valign="top" align="left">214.04(145.62, 304.36)</td>
</tr>
<tr>
<td valign="top" align="left">&#x2003;50-59</td>
<td valign="top" align="left">424</td>
<td valign="top" align="left">200.70(140.35, 280.45)</td>
</tr>
<tr>
<td valign="top" align="left">&#x2003;60-69</td>
<td valign="top" align="left">263</td>
<td valign="top" align="left">188.65(125.61,268.87)</td>
</tr>
<tr>
<td valign="top" align="left">&#x2003;&#x2265;70</td>
<td valign="top" align="left">190</td>
<td valign="top" align="left">164.61(114.53,237.25)</td>
</tr>
</tbody>
</table>
</table-wrap>
</sec>
<sec id="s4_3">
<label>4.3</label>
<title>Comparison of iodine nutrition status among adults and different genders and regions</title>
<p>The percentages of mild iodine deficiency, moderate iodine deficiency, severe iodine deficiency, adequate iodine intake(AI), more than adequate iodine intake(MAI)and excessive iodine intake(EI)were8.41%, 2.17%, 0.26%, 33.22%, 28.35%, and27.59%, respectively. The percentages of mild, moderate and severe iodine deficiency in urban populations (7.13%, 0.87%, 0.0%) were significantly lower than those in rural populations (9.81%, 3.59%, 0.56%) (P &lt; 0.05), and the rate of adequate, more than adequate iodine intake in urban populations (36.03%, 30.93%) were significantly higher than that in rural populations (30.14%, 25.52%). The rate of excess iodine intake was higher in rural populations (30.38%) than in urban populations (25.04%). Female and male had similar nutritional status (P&gt;0.05) (<xref ref-type="table" rid="T4"><bold>Table&#xa0;4</bold></xref>).</p>
<table-wrap id="T4" position="float">
<label>Table&#xa0;4</label>
<caption>
<p>Comparison of adult iodine nutrition and iodine nutrition by gender and population.</p>
</caption>
<table frame="hsides">
<thead>
<tr>
<th valign="top" rowspan="2" align="left">Iodine state</th>
<th valign="top" rowspan="2" align="left">N</th>
<th valign="top" colspan="2" align="left">Male<break/>(n=1358)</th>
<th valign="top" colspan="2" align="left">Female<break/>(n=1270)</th>
<th valign="bottom" rowspan="2" align="left">&#x3c7;<sup>2</sup>
</th>
<th valign="bottom" rowspan="2" align="left"><italic>P</italic>
</th>
<th valign="top" colspan="2" align="left">Urban<break/>(n=1374)</th>
<th valign="top" colspan="2" align="left">Rural<break/>(n=1254)</th>
<th valign="bottom" rowspan="2" align="left">&#x3c7;<sup>2</sup>
</th>
<th valign="bottom" rowspan="2" align="left"><italic>P</italic>
</th>
</tr>
<tr>
<th valign="top" align="left">n</th>
<th valign="top" align="left">Percentage/%</th>
<th valign="top" align="left">n</th>
<th valign="top" align="left">Percentage/%</th>
<th valign="top" align="left">n</th>
<th valign="top" align="left">Percentage/%</th>
<th valign="top" align="left">n</th>
<th valign="top" align="left">Percentage/%</th>
</tr>
</thead>
<tbody>
<tr>
<td valign="top" align="left">Mild iodine deficiency</td>
<td valign="top" align="left">221</td>
<td valign="top" align="left">105</td>
<td valign="top" align="left">7.73</td>
<td valign="top" align="left">116</td>
<td valign="top" align="left">9.13</td>
<td valign="top" align="left">1.68</td>
<td valign="top" align="left">0.195</td>
<td valign="top" align="left">98</td>
<td valign="top" align="left">7.13</td>
<td valign="top" align="left">123</td>
<td valign="top" align="left">9.81</td>
<td valign="top" align="left">6.23</td>
<td valign="top" align="left">0.013</td>
</tr>
<tr>
<td valign="top" align="left">Moderate iodine deficiency</td>
<td valign="top" align="left">57</td>
<td valign="top" align="left">26</td>
<td valign="top" align="left">1.91</td>
<td valign="top" align="left">31</td>
<td valign="top" align="left">2.44</td>
<td valign="top" align="left">0.86</td>
<td valign="top" align="left">0.354</td>
<td valign="top" align="left">12</td>
<td valign="top" align="left">0.87</td>
<td valign="top" align="left">45</td>
<td valign="top" align="left">3.59</td>
<td valign="top" align="left">22.91</td>
<td valign="top" align="left">0.000</td>
</tr>
<tr>
<td valign="top" align="left">Severe iodine deficiency</td>
<td valign="top" align="left">7</td>
<td valign="top" align="left">4</td>
<td valign="top" align="left">0.29</td>
<td valign="top" align="left">3</td>
<td valign="top" align="left">0.24</td>
<td valign="top" align="left">0.08</td>
<td valign="top" align="left">0.772</td>
<td valign="top" align="left">0</td>
<td valign="top" align="left">0.0</td>
<td valign="top" align="left">7</td>
<td valign="top" align="left">0.56</td>
<td valign="top" align="left">7.71</td>
<td valign="top" align="left">0.005</td>
</tr>
<tr>
<td valign="top" align="left">Adequate iodine intake(AI)</td>
<td valign="top" align="left">872</td>
<td valign="top" align="left">440</td>
<td valign="top" align="left">32.40</td>
<td valign="top" align="left">432</td>
<td valign="top" align="left">34.02</td>
<td valign="top" align="left">0.87</td>
<td valign="top" align="left">0.35</td>
<td valign="top" align="left">495</td>
<td valign="top" align="left">36.03</td>
<td valign="top" align="left">379</td>
<td valign="top" align="left">30.22</td>
<td valign="top" align="left">11.83</td>
<td valign="top" align="left">0.001</td>
</tr>
<tr>
<td valign="top" align="left">More than adequate iodine intake(MAI)</td>
<td valign="top" align="left">745</td>
<td valign="top" align="left">400</td>
<td valign="top" align="left">29.46</td>
<td valign="top" align="left">345</td>
<td valign="top" align="left">27.17</td>
<td valign="top" align="left">1.40</td>
<td valign="top" align="left">0.237</td>
<td valign="top" align="left">425</td>
<td valign="top" align="left">30.93</td>
<td valign="top" align="left">320</td>
<td valign="top" align="left">25.52</td>
<td valign="top" align="left">9.01</td>
<td valign="top" align="left">0.003</td>
</tr>
<tr>
<td valign="top" align="left">Excessive iodine intake(EI)</td>
<td valign="top" align="left">725</td>
<td valign="top" align="left">383</td>
<td valign="top" align="left">28.20</td>
<td valign="top" align="left">342</td>
<td valign="top" align="left">26.93</td>
<td valign="top" align="left">0.53</td>
<td valign="top" align="left">0.468</td>
<td valign="top" align="left">344</td>
<td valign="top" align="left">25.04</td>
<td valign="top" align="left">381</td>
<td valign="top" align="left">30.38</td>
<td valign="top" align="left">9.74</td>
<td valign="top" align="left">0.002</td>
</tr>
</tbody>
</table>
</table-wrap>
</sec>
<sec id="s4_4">
<label>4.4</label>
<title>Detection of thyroid diseases in adults</title>
<p>Thyroid diseases are detected in residents based on biochemical indicators such as TSH, FT3, and FT4, as the well as Doppler ultrasound color of the thyroid. The prevalence of thyroid disorders in adults were as follows: 1.20% of clinical hyperthyroidism, 0.2% of subclinical hyperthyroidism, 1.00% of clinical hypothyroidism, 29.20% of subclinical hypothyroidism, 9.80% of positive TPO Ab, 9.20% of positive TG Ab, 2.10% of goiter, 6.40% of single thyroid nodules and 1.80% of multiple nodules. The detection rate of subclinical hypothyroidism is as high as 29.20% (<xref ref-type="table" rid="T5"><bold>Table&#xa0;5</bold></xref>).</p>
<table-wrap id="T5" position="float">
<label>Table&#xa0;5</label>
<caption>
<p>Detection of thyroid diseases in adults of different sexes and population.</p>
</caption>
<table frame="hsides">
<thead>
<tr>
<th valign="top" rowspan="2" align="left">thyroid disease</th>
<th valign="top" rowspan="2" align="left">N</th>
<th valign="top" colspan="2" align="left">Male<break/>(n=1358)</th>
<th valign="top" colspan="2" align="left">Female<break/>(n=1270)</th>
<th valign="bottom" rowspan="2" align="left">&#x3c7;<sup>2</sup>
</th>
<th valign="bottom" rowspan="2" align="left"><italic>P</italic>
</th>
<th valign="top" colspan="2" align="left">Urban<break/>(n=1374)</th>
<th valign="top" colspan="2" align="left">Rural<break/>(n=1254)</th>
<th valign="bottom" rowspan="2" align="left">&#x3c7;<sup>2</sup>
</th>
<th valign="bottom" rowspan="2" align="left"><italic>P</italic>
</th>
</tr>
<tr>
<th valign="top" align="left">n</th>
<th valign="top" align="left">Percentage /%</th>
<th valign="top" align="left">n</th>
<th valign="top" align="left">Percentage /%</th>
<th valign="top" align="left">n</th>
<th valign="top" align="left">Percentage /%</th>
<th valign="top" align="left">n</th>
<th valign="top" align="left">Percentage /%</th>
</tr>
</thead>
<tbody>
<tr>
<td valign="top" align="left">Clinical hyperthyroidism</td>
<td valign="top" align="left">31</td>
<td valign="top" align="left">17</td>
<td valign="top" align="left">1.25</td>
<td valign="top" align="left">14</td>
<td valign="top" align="left">1.10</td>
<td valign="top" align="left">0.13</td>
<td valign="top" align="left">0.723</td>
<td valign="top" align="left">19</td>
<td valign="top" align="left">1.38</td>
<td valign="top" align="left">12</td>
<td valign="top" align="left">0.96</td>
<td valign="top" align="left">1.02</td>
<td valign="top" align="left">0.312</td>
</tr>
<tr>
<td valign="top" align="left">Subclinical hyperthyroidism</td>
<td valign="top" align="left">4</td>
<td valign="top" align="left">2</td>
<td valign="top" align="left">0.15</td>
<td valign="top" align="left">2</td>
<td valign="top" align="left">0.16</td>
<td valign="top" align="left">0.00</td>
<td valign="top" align="left">0.947</td>
<td valign="top" align="left">3</td>
<td valign="top" align="left">0.22</td>
<td valign="top" align="left">1</td>
<td valign="top" align="left">0.08</td>
<td valign="top" align="left">0.83</td>
<td valign="top" align="left">0.363</td>
</tr>
<tr>
<td valign="top" align="left">Clinical hypothyroidism</td>
<td valign="top" align="left">27</td>
<td valign="top" align="left">9</td>
<td valign="top" align="left">0.66</td>
<td valign="top" align="left">18</td>
<td valign="top" align="left">1.42</td>
<td valign="top" align="left">3.67</td>
<td valign="top" align="left">0.055</td>
<td valign="top" align="left">8</td>
<td valign="top" align="left">0.58</td>
<td valign="top" align="left">19</td>
<td valign="top" align="left">1.52</td>
<td valign="top" align="left">5.62</td>
<td valign="top" align="left">0.018</td>
</tr>
<tr>
<td valign="top" align="left">Subclinical hypothyroidism</td>
<td valign="top" align="left">768</td>
<td valign="top" align="left">320</td>
<td valign="top" align="left">23.58</td>
<td valign="top" align="left">448</td>
<td valign="top" align="left">35.28</td>
<td valign="top" align="left">43.40</td>
<td valign="top" align="left">0.000</td>
<td valign="top" align="left">355</td>
<td valign="top" align="left">25.84</td>
<td valign="top" align="left">413</td>
<td valign="top" align="left">32.96</td>
<td valign="top" align="left">16.01</td>
<td valign="top" align="left">0.000</td>
</tr>
<tr>
<td valign="top" align="left">Goiter</td>
<td valign="top" align="left">56</td>
<td valign="top" align="left">13</td>
<td valign="top" align="left">0.96</td>
<td valign="top" align="left">43</td>
<td valign="top" align="left">3.39</td>
<td valign="top" align="left">18.49</td>
<td valign="top" align="left">0.000</td>
<td valign="top" align="left">19</td>
<td valign="top" align="left">1.38</td>
<td valign="top" align="left">37</td>
<td valign="top" align="left">2.96</td>
<td valign="top" align="left">7.75</td>
<td valign="top" align="left">0.005</td>
</tr>
<tr>
<td valign="top" align="left">Single thyroid nodule</td>
<td valign="top" align="left">169</td>
<td valign="top" align="left">78</td>
<td valign="top" align="left">5.74</td>
<td valign="top" align="left">91</td>
<td valign="top" align="left">7.17</td>
<td valign="top" align="left">2.20</td>
<td valign="top" align="left">0.138</td>
<td valign="top" align="left">110</td>
<td valign="top" align="left">8.01</td>
<td valign="top" align="left">59</td>
<td valign="top" align="left">4.70</td>
<td valign="top" align="left">11.87</td>
<td valign="top" align="left">0.001</td>
</tr>
<tr>
<td valign="top" align="left">Multinodular thyroid gland</td>
<td valign="top" align="left">46</td>
<td valign="top" align="left">20</td>
<td valign="top" align="left">1.47</td>
<td valign="top" align="left">26</td>
<td valign="top" align="left">2.05</td>
<td valign="top" align="left">0.02</td>
<td valign="top" align="left">0.262</td>
<td valign="top" align="left">22</td>
<td valign="top" align="left">1.60</td>
<td valign="top" align="left">24</td>
<td valign="top" align="left">1.91</td>
<td valign="top" align="left">0.34</td>
<td valign="top" align="left">0.541</td>
</tr>
<tr>
<td valign="top" align="left">TPO Ab positivity</td>
<td valign="top" align="left">257</td>
<td valign="top" align="left">85</td>
<td valign="top" align="left">6.26</td>
<td valign="top" align="left">172</td>
<td valign="top" align="left">13.54</td>
<td valign="top" align="left">39.47</td>
<td valign="top" align="left">0.000</td>
<td valign="top" align="left">145</td>
<td valign="top" align="left">10.55</td>
<td valign="top" align="left">112</td>
<td valign="top" align="left">8.93</td>
<td valign="top" align="left">1.95</td>
<td valign="top" align="left">0.168</td>
</tr>
<tr>
<td valign="top" align="left">TG Ab positivity</td>
<td valign="top" align="left">242</td>
<td valign="top" align="left">65</td>
<td valign="top" align="left">4.79</td>
<td valign="top" align="left">177</td>
<td valign="top" align="left">13.94</td>
<td valign="top" align="left">65.73</td>
<td valign="top" align="left">0.000</td>
<td valign="top" align="left">136</td>
<td valign="top" align="left">9.90</td>
<td valign="top" align="left">106</td>
<td valign="top" align="left">8.45</td>
<td valign="top" align="left">1.64</td>
<td valign="top" align="left">0.201</td>
</tr>
</tbody>
</table>
</table-wrap>
<p>The detection rates of subclinical hypothyroidism, and goiter were significantly higher in females (35.28%, 3.39%) than those in males (23.58%, 0.96%) (P &lt; 0.05), and the positive rates of TPO Ab and TG Ab were significantly higher in females (13.54%, 13.94%) (P &lt; 0.05). The detection rates of clinical hypothyroidism, subclinical hypothyroidism, and nodular goiter were significantly higher in rural populations (1.52%, 32.96%, 2.96%) than those in urban populations (0.58%, 25.84%,1.38%) (P &lt; 0.05).</p>
</sec>
<sec id="s4_5">
<label>4.5</label>
<title>Thyroid diseases and iodine nutritional status</title>
<p>As show in <xref ref-type="table" rid="T6"><bold>Table&#xa0;6</bold></xref>, under different iodine nutrition statuses, there was no significant difference in the prevalence of clinical hyperthyroidism, subclinical hyperthyroidism, subclinical hypothyroidism, nodular goite, thyroid nodules detected, and positive rates of TPO Ab and TG Ab (P &gt; 0.05). The detection rate of clinical hypothyroidism was statistically significant in different iodine nutritional states (P&lt; 0.05).</p>
<table-wrap id="T6" position="float">
<label>Table&#xa0;6</label>
<caption>
<p>Prevalence of thyroid diseases among people with different iodine nutritional status.</p>
</caption>
<table frame="hsides">
<thead>
<tr>
<th valign="top" rowspan="2" align="left">thyroid disease</th>
<th valign="top" colspan="2" align="left">Deficient iodine intake(n=297)</th>
<th valign="top" colspan="2" align="left">Adequate iodine intake(n=861)</th>
<th valign="top" colspan="2" align="left">More than adequate iodine intake(n=745)</th>
<th valign="top" colspan="2" align="left">Excessive iodine intake(n=725)</th>
<th valign="bottom" rowspan="2" align="left">&#x3c7;<sup>2</sup>
</th>
<th valign="bottom" rowspan="2" align="left"><italic>P</italic>
</th>
</tr>
<tr>
<th valign="top" align="left">n</th>
<th valign="top" align="left">Percentage /%</th>
<th valign="top" align="left">n</th>
<th valign="top" align="left">Percentage /%</th>
<th valign="top" align="left">n</th>
<th valign="top" align="left">Percentage /%</th>
<th valign="top" align="left">n</th>
<th valign="top" align="left">Percentage /%</th>
</tr>
</thead>
<tbody>
<tr>
<td valign="top" align="left">Clinical hyperthyroidism</td>
<td valign="top" align="left">2</td>
<td valign="top" align="left">0.67</td>
<td valign="top" align="left">9</td>
<td valign="top" align="left">1.06</td>
<td valign="top" align="left">10</td>
<td valign="top" align="left">1.34</td>
<td valign="top" align="left">10</td>
<td valign="top" align="left">1.38</td>
<td valign="top" align="left">1.17</td>
<td valign="top" align="left">0.761</td>
</tr>
<tr>
<td valign="top" align="left">Subclinical hyperthyroidism</td>
<td valign="top" align="left">0</td>
<td valign="top" align="left">0.00</td>
<td valign="top" align="left">1</td>
<td valign="top" align="left">0.12</td>
<td valign="top" align="left">2</td>
<td valign="top" align="left">0.27</td>
<td valign="top" align="left">1</td>
<td valign="top" align="left">0.14</td>
<td valign="top" align="left">1.19</td>
<td valign="top" align="left">0.756</td>
</tr>
<tr>
<td valign="top" align="left">Clinical hypothyroidism</td>
<td valign="top" align="left">8</td>
<td valign="top" align="left">2.69</td>
<td valign="top" align="left">6</td>
<td valign="top" align="left">0.71</td>
<td valign="top" align="left">5</td>
<td valign="top" align="left">0.67</td>
<td valign="top" align="left">7</td>
<td valign="top" align="left">0.97</td>
<td valign="top" align="left">10.22</td>
<td valign="top" align="left">0.017</td>
</tr>
<tr>
<td valign="top" align="left">Subclinical hypothyroidism</td>
<td valign="top" align="left">81</td>
<td valign="top" align="left">27.27</td>
<td valign="top" align="left">265</td>
<td valign="top" align="left">30.78</td>
<td valign="top" align="left">203</td>
<td valign="top" align="left">26.57</td>
<td valign="top" align="left">228</td>
<td valign="top" align="left">29.84</td>
<td valign="top" align="left">3.79</td>
<td valign="top" align="left">0.285</td>
</tr>
<tr>
<td valign="top" align="left">Goiter</td>
<td valign="top" align="left">8</td>
<td valign="top" align="left">2.70</td>
<td valign="top" align="left">19</td>
<td valign="top" align="left">2.24</td>
<td valign="top" align="left">8</td>
<td valign="top" align="left">1.08</td>
<td valign="top" align="left">21</td>
<td valign="top" align="left">2.90</td>
<td valign="top" align="left">6.49</td>
<td valign="top" align="left">0.090</td>
</tr>
<tr>
<td valign="top" align="left">Single thyroid nodule</td>
<td valign="top" align="left">21</td>
<td valign="top" align="left">7.07</td>
<td valign="top" align="left">62</td>
<td valign="top" align="left">7.30</td>
<td valign="top" align="left">50</td>
<td valign="top" align="left">6.71</td>
<td valign="top" align="left">36</td>
<td valign="top" align="left">4.97</td>
<td valign="top" align="left">3.94</td>
<td valign="top" align="left">0.268</td>
</tr>
<tr>
<td valign="top" align="left">Multinodular thyroid gland</td>
<td valign="top" align="left">3</td>
<td valign="top" align="left">1.01</td>
<td valign="top" align="left">16</td>
<td valign="top" align="left">1.88</td>
<td valign="top" align="left">12</td>
<td valign="top" align="left">1.61</td>
<td valign="top" align="left">15</td>
<td valign="top" align="left">2.07</td>
<td valign="top" align="left">1.54</td>
<td valign="top" align="left">0.673</td>
</tr>
<tr>
<td valign="top" align="left">TPO Ab positivity</td>
<td valign="top" align="left">33</td>
<td valign="top" align="left">11.11</td>
<td valign="top" align="left">88</td>
<td valign="top" align="left">10.37</td>
<td valign="top" align="left">64</td>
<td valign="top" align="left">8.59</td>
<td valign="top" align="left">70</td>
<td valign="top" align="left">9.66</td>
<td valign="top" align="left">2.13</td>
<td valign="top" align="left">0.545</td>
</tr>
<tr>
<td valign="top" align="left">TG Ab positivity</td>
<td valign="top" align="left">27</td>
<td valign="top" align="left">9.09</td>
<td valign="top" align="left">79</td>
<td valign="top" align="left">9.31</td>
<td valign="top" align="left">58</td>
<td valign="top" align="left">7.79</td>
<td valign="top" align="left">76</td>
<td valign="top" align="left">10.48</td>
<td valign="top" align="left">3.24</td>
<td valign="top" align="left">0.357</td>
</tr>
</tbody>
</table>
</table-wrap>
</sec>
</sec>
<sec id="s5" sec-type="discussion">
<label>5</label>
<title>Discussion</title>
<p>By synthesizing thyroid stimulating hormone (TH), iodine plays a crucial role in the growth of the body and in the development of tissue morphology. Insufficient THS production caused by iodine deficiency can lead to endemic goiter, cretinism, hypothyroidism, and even thyroid cancer (<xref ref-type="bibr" rid="B6">6</xref>). However, long-term excessive iodine exposure can lead to iodine induced hyperthyroidism, iodine excess goiter, chronic lymphocytic thyroiditis, and hypothyroidism (<xref ref-type="bibr" rid="B7">7</xref>). The Qinghai Province is situated in northwest China, on the Qinghai-Tibet Plateau. Qinghai Province is currently suffering from widespread iodine deficiency in the external environment. The implementation and continuous adjustment of USI policies have effectively controlled iodine deficiency disorder (IDD) (<xref ref-type="bibr" rid="B5">5</xref>). However, in the past 20 years, there have been no systematic reports on the epidemiology of thyroid diseases in our province. The iodine nutritional status is biased towards key populations in a certain region (<xref ref-type="bibr" rid="B8">8</xref>), specific ethnic groups in a certain region (<xref ref-type="bibr" rid="B9">9</xref>), or iodine deficiency disease testing (<xref ref-type="bibr" rid="B10">10</xref>, <xref ref-type="bibr" rid="B11">11</xref>), lacking large-scale surveys. In addition, there are no reports of a correlation between iodine nutritional status and thyroid diseases.</p>
<p>In this study, a total of 2628 valid datas were obtained, and we found that the median UIC of the overall population was 217.90 ug/L, with a median UIC of 220.84 ug/L for males and 213.87 ug/L for females, which was higher than the national median urinary iodine of 177.89 &#x3bc;g/L of adults during the same period level (<xref ref-type="bibr" rid="B12">12</xref>). The recommended urine iodine level for normal adults in China is 100-200 ug/L. Therefore, the urine iodine level for adults in our province currently falls within the iodine excess range specified in the WHO/UNICEF/ICCIDD standard. By further grouping the age groups, the iodine intake of young and middle-aged people is relatively high, which may be related to the large dietary intake, multiple types, and excessive iodine salt intake of such people. The extent of iodine deficiency and the rate of iodine overdose are higher in rural areas. Iodine deficiency may be related to residents&#x2019; irregular iodized salt intake, such as poor economic conditions, reluctance to buy iodized salt, and purchase un-iodized salt on their own. The higher rate of excess iodine intake may be related to the high number of young people in the age group of 18-29 years old.</p>
<p>This study found that the detection rates of clinical hyperthyroidism, subclinical hyperthyroidism, clinical hypothyroidism, and goiter in Qinghai Province (1.20%, 0.20%, 1.00%, 2.10%) were similar to the overall national level (0.78%, 0.44%, 1.02%, 1.17%) during the same period of the TIDE study, and the positive rates of TPO Ab and TG Ab antibodies (9.80%, 9.20%) were also relatively stable compared to the TIDE study (10.19%, 9.70%). Subclinical hypothyroidism (29.20%) was higher than the national level (12.93%) during the same period, Subclinical hypothyroidism is detected at a significantly higher rate than the national average. The global reported data showed that clinical hyperthyroidism was 0.2%-1.3% (<xref ref-type="bibr" rid="B13">13</xref>), subclinical hyperthyroidism was 1% to 5% (<xref ref-type="bibr" rid="B14">14</xref>), and clinical hypothyroidism was 0.2-5.3% (<xref ref-type="bibr" rid="B13">13</xref>). In contrast, our data are generally consistent. Nevertheless, excessive iodine consumption in the diet may be contributing to an increase in the incidence rate of subclinical hypothyroidism in the population (<xref ref-type="bibr" rid="B15">15</xref>). Chronic long-term stimulation of excessive iodine may be the factor that iodine induces hypothyroidism. Furthermore, the detection rate was higher among female than among male, and in rural areas than in urban ones. However, the detection rate did not differ significantly among patients with different levels of urinary iodine.</p>
<p>Thyroid diseases can be caused by insufficient or excessive iodine intake, according to previous studies (<xref ref-type="bibr" rid="B16">16</xref>, <xref ref-type="bibr" rid="B17">17</xref>). Subclinical hypothyroidism is associated with an increase in iodine intake in iodine-deficient populations. However, it has also been reported that there is no correlation between iodine nutritional status and thyroid disease. In this study, no correlation was found between iodine and subclinical hypothyroidism. Further research is needed to clarify the reference range of TSH and the correlation between iodine and thyroid function in normal populations in Qinghai Province.</p>
<p>According to this study, 8.2% of thyroid nodules are detected in Qinghai Province, less than 49.0% in Beijing (<xref ref-type="bibr" rid="B18">18</xref>), 36,88% in Heilongjiang (<xref ref-type="bibr" rid="B19">19</xref>), and 27.8% in Shanghai (<xref ref-type="bibr" rid="B20">20</xref>), and less than the overall national level of 20.43% during the same period. Female are most likely to be detected with goiter than male, and urban areas have a higher detection rate than rural areas. This result is consistent with adult domestic and foreign adult data (<xref ref-type="bibr" rid="B21">21</xref>, <xref ref-type="bibr" rid="B22">22</xref>). There is an association between higher iodine intake and a lower prevalence of thyroid nodules in the TIDE study (<xref ref-type="bibr" rid="B3">3</xref>). However, we found no significant association between thyroid nodules and people with different urinary iodine levels. Therefore, the specific mechanism of thyroid nodules remains unclear. It has been reported that thyroid nodules may be related to genetics, economic development, lifestyle, and more exposure to radiation among urban populations, atmospheric and water pollution, as well as psychological stress and other predisposing factors for thyroid nodules (<xref ref-type="bibr" rid="B23">23</xref>, <xref ref-type="bibr" rid="B24">24</xref>). More research is needed to analyze the cause.</p>
<p>We found that the detection rate of hypothyroidism in people with iodine deficiency is higher than in other iodine nutritional situations. Many studies have reported that low urinary iodine levels are associated with decreased thyroid function. Iodine deficiency or excessive nutrition can easily increase the prevalence of clinical and subclinical hypothyroidism (<xref ref-type="bibr" rid="B1">1</xref>). There were no statistical differences in the detection rates of other diseases among populations with different iodine intakes, which may be due to sampling reasons or other learning disturbances, etc.</p>
<p>This study is the first epidemiological investigation to comprehensively evaluate iodine nutrition and thyroid diseases in Qinghai Province. We found that the iodine nutrition level in Qinghai Province is currently in excess of iodine. The prevalence of most thyroid diseases remained stable, with a paradoxical significant decrease in the rate of thyroid nodule detection and a significant increase in the proportion of subclinical hypothyroidism. It should continue to be implemented and monitored, while actively searching for the causes of subclinical hypothyroidism and taking the corresponding countermeasures. The incidence rate of thyroid nodules is low, but the detection of malignancy should be done well. The inadequacies of this article are due to the fact that only two residential communities in urban and rural areas were selected, and the samples couldn&#x2019;t represent the entire population. Furthermore, Qinghai province has a different high altitudes, and whether there are differences between different altitudes requires further research.</p>
</sec>
<sec id="s6" sec-type="data-availability">
<title>Data availability statement</title>
<p>The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.</p>
</sec>
<sec id="s7" sec-type="ethics-statement">
<title>Ethics statement</title>
<p>The research protocols were approved by the Medical Ethics Committee of China Medical University. All subjects were provided written informed consent following a thorough explanation of the research procedures. Some measures were taken to ensure the project quality. The studies were conducted in accordance with the local legislation and institutional requirements. Written informed consent for participation in this study was provided by the participants&#x2019; legal guardians/next of kin.</p>
</sec>
<sec id="s8" sec-type="author-contributions">
<title>Author contributions</title>
<p>XF, LZ, and CC collect data and write the article. All authors contributed to the article and approved the submitted version.</p>
</sec>
</body>
<back>
<sec id="s9" sec-type="funding-information">
<title>Funding</title>
<p>The authors declare that no financial support was received for the research, authorship, and/or publication of this article.</p>
</sec>
<ack>
<title>Acknowledgments</title>
<p>We apologize to investigators whose contributions were not cited due to space limitations.</p>
</ack>
<sec id="s10" sec-type="COI-statement">
<title>Conflict of interest</title>
<p>The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.</p>
</sec>
<sec id="s11" sec-type="disclaimer">
<title>Publisher&#x2019;s note</title>
<p>All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.</p>
</sec>
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