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Context: In 2015, we reported an increased prevalence of thyroid disease in a county of low habitual selenium (Se) intake in comparison to a neighboring county with higher intake in a cross-sectional survey in Shaanxi Province, China., Objective: To explore longitudinal effects of low Se status, a prospective cohort study was conducted in the same area from 2013 to 2019, and thyroid peroxidase autoantibodies (TPO-Abs) and disease incidence were compared., Methods: A total 1254 individuals from 1500 reinvited participants were successfully enrolled. Venous blood, fingernails, and urine samples were collected and analyzed to evaluate thyroid status, TPO-Abs, serum Se, and urinary iodine. Diagnosis of Hashimoto thyroiditis (HT) was based on elevated thyrotropin, presence of TPO-Abs, and ultrasound characteristics. Se deficiency was categorized using a serum concentration of 80 µg/L as a threshold, and tested by logistic regression for a relationship to TPO-Abs and HT., Results: Se deficiency was observed in 46.2% of participants from the adequate-Se county (Ziyang) and in 89.7% from the low-Se county (Ningshan). Se concentrations in fingernails differed strongly by residency (Ziyang vs Ningshan; 678.7 vs 364.3 μg/kg; Z = -9.552; P < .001). Newly diagnosed HT in Ziyang was less frequent than in Ningshan (0.09% vs 0.31%; χ 2 = 4.350; P = .037). The conversion rate to seropositive TPO-Abs was 10.2% in Ningshan vs 5.6% in Ziyang. Excluding iodine as confounding factor, low-Se was confirmed as a risk factor for HT (relative risk [95% CI]; 3.65 [1.03-12.90]; P < .05)., Conclusion: The data indicate an increased incidence of TPO-Ab seroconversion with low Se supply and support the hypothesis that Se deficiency contributes to HT as a modifiable risk factor., (© The Author(s) 2022. Published by Oxford University Press on behalf of the Endocrine Society. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

Background: Despite the implementation of the universal salt iodization (USI) program for correction of iodine deficiency in China for ∼20 years, the actual iodine nutrition status of Chinese residents and the prevalence of iodine deficiency and iodine excess are issues that need to be addressed. This nationally representative cross-sectional study was conducted across all 31 provinces of mainland China to gather extensive data on iodine nutrition status and the influential factors. Methods: This study included 78,470 participants, aged 18 years or older, who were interviewed and asked to answer a questionnaire. Urine iodine concentration (UIC) was measured by the inductively coupled plasma mass spectrometry method, and goiter was examined by thyroid ultrasonography. In addition, sixty 9-11 years old school children in each province were randomly selected to evaluate the UIC and thyroid ultrasonography. The iodine nutrition status was determined according to the World Health Organization guidelines. Results: The iodized salt coverage was 95.37%. The median urine iodine (MUI) was 177.89 μg/L (interquartile range [IQR], 117.89-263.90 μg/L) and goiter prevalence was 1.17% (confidence interval [95% CI 0.95-1.43]) in the adult population. The MUI was 199.75 μg/L (IQR, 128.41-303.37 μg/L) in school-age children, and goiter prevalence was 3.50% [95% CI, 2.93-4.13]. The percentage of individuals with UIC <50 μg/L was 3.43%, <20%. Analysis indicated that sex, age, geographic factors, body mass index, and smoking habits influence the iodine nutrition level. Conclusion: The mandatory USI program has successfully eliminated iodine deficiency disorders, and the findings indicate that the iodine nutrition level in the general population is within the safe range.

Background: Universal salt iodization (USI) was implemented in mainland China in 1996. The prevalence of hyperthyroidism and its risk factors now require examination., Methods: Data were acquired from a nationwide Thyroid, Iodine, and Diabetes Epidemiological survey (TIDE 2015-2017) of 78,470 subjects from 31 provinces. Iodine status, and thyroid hormones and antibodies were measured., Results: After two decades of USI, the prevalence of overt hyperthyroidism (OH), Graves' disease (GD), severe subclinical hyperthyroidism (severe SCH), and mild subclinical hyperthyroidism (mild SCH) in mainland China was 0.78%, 0.53%, 0.22%, and 0.22%, respectively. OH and GD prevalence were higher in women than in men (OH: 1.16% vs . 0.64%, P<0.001; GD: 0.65% vs . 0.37%, P<0.001).Prevalence was significantly decreased after 60 years-of-age compared with 30-39 years-of-age (OH:0.61% vs . 0.81%, P<0.001; GD: 0.38% vs . 0.57%, P<0.001).Excessive iodine(EI) and deficient iodine(DI) were both related to increased prevalence of OH (odds ratio [OR] 2.09, 95% confidence interval [CI] 1.68-2.59; OR1.35, 95%CI 1.07-1.72, respectively); however, only deficient iodine was associated with increased prevalence of GD (OR1.67, 95%CI 1.30-2.15). Increased thyroid peroxidase antibody and thyroglobulin antibody levels were significantly associated with prevalence of OH and GD, but not severe SCH and mild SCH. Although hyperthyroidism was more prevalent in women, the association disappeared after adjusting for other factors such as antibody levels., Conclusion: OH and GD prevalences in mainland China are stable after two decades of USI. Iodine deficiency, elevated thyroid antibody levels, and middle age are the main risk factors for OH and GD. The severe SCH population, rather than the mild SCH population, shows similar characteristics to the OH population., Competing Interests: 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., (Copyright © 2021 Wang, Li, Teng, Shi, Ba, Chen, Du, He, Lai, Li, Chi, Liao, Liu, Liu, Qin, Qin, Quan, Shi, Sun, Tang, Tong, Wang, Zhang, Wang, Xue, Yan, Yang, Yang, Yao, Ye, Zhang, Zhang, Zhu, Zhu, Shan and Teng.)

Background: Associations between iodine intake and thyroid nodules (TNs) were not consistent. We aimed to illustrate the relationship between urinary iodine concentration (UIC) and TNs., Methods: A total of 12,698 participants were enrolled in analysis. All of the participants filled out questionnaires and underwent physical examinations, laboratory tests, and thyroid ultrasonography. UIC, serum thyrotropin (TSH), thyroid peroxidase antibodies (TPOAb), and thyroglobulin antibodies (TgAb) were measured in the central laboratory., Results: The prevalence of TNs was 16.00%, and the median UIC was 206.1  μ g/L. TNs and UIC were negatively related when UIC was less than 527  μ g/L (adjusted OR = 0.87; 95% CI, 0.80, 0.94), and the relationship between UIC and TNs was not statistically significant when UIC was greater than 527  μ g/L (adjusted OR = 1.25; 95% CI, 0.98, 1.60). In women, UIC was negatively associated with risk for TNs (adjusted OR 0.95; 95% CI, 0.91, 0.99)., Conclusion: The relationship between TNs and UIC differed between men and women. The risk of TNs decreased with the elevation of UIC in men when UIC was lower than 527  μ g/L, while UIC and the presence of TNs were negatively correlated in women. In the future, cohort studies or other studies that can explain causality must be conducted to explore the relationship between iodine status and TNs., Competing Interests: The authors declare that there is no conflict of interest regarding the publication of this article., (Copyright © 2020 Hui Sun et al.)

Background: Subclinical hypothyroidism is diagnosed based on serum thyrotropin (TSH) reference intervals, which in turn are affected by many factors. Methods: Data were acquired from a Chinese nationally representative cross-sectional study of 78,470 participants (TIDE study). The total study population were participants from the TIDE program, and the reference population was a subset of the total population defined by the National Academy of Clinical Biochemistry (NACB) guidelines. Serum concentrations of thyroid hormones, TSH, thyroid antibodies, and urine iodine concentration (UIC) were measured. Results: The geometric mean serum TSH (2.5th-97.5th) for the reference population (defined by the NACB) and total population was 2.28 mIU/L (0.74-7.04 mIU/L) and 2.34 mIU/L (0.61-8.33 mIU/L), respectively. In the reference population, increase in UIC was significantly associated with increase in the 50th and 97.5th centiles and decrease in the 2.5th centile of TSH. The median TSH was significantly higher in women than in men (2.41 mIU/L vs. 2.16 mIU/L, p -value <0.001). Increased age was significantly associated with an increased TSH, 97.5th centile. For each 10-year increase in the population age, the TSH 97.5th centile increased by 0.534 mIU/L. The prevalence of subclinical hypothyroidism diagnosed according to the assay-recommended interval (Roche 0.27-4.2 mIU/L) and NACB standard interval in the TIDE study (0.74-7.04 mIU/L) differed significantly (Roche 13.61% vs. TIDE 3.00%, p  < 0.05). However, there was no significant difference in future cardiovascular disease, reflected by the Framingham risk score, between the 0.27-4.2 and 4.2-7.04 mIU/L TSH groups. Conclusions: Serum TSH concentration significantly increased with increase in iodine intake. Thus, iodine intake must be considered in establishing TSH reference intervals. To avoid overdiagnosis and overtreatment of subclinical hypothyroidism, different areas should use individual serum TSH reference intervals.

Background and Aims: Iodine is one of the most important trace elements in the human body. It is not only the main component of thyroid hormones but also has extrathyroid biological functions. To date, there have been no large-scale epidemiological studies on the relationship between hyperuricemia and iodine intake, although both are closely related to health. A population-based epidemiological survey in China offers such an opportunity., Methods: This population-based cross-sectional study recruited 75,653 adults aged ≥ 18 years from 2015 to 2017 with a randomized, multistage, stratified sampling strategy. Serum uric acid levels and urinary iodine concentrations (UICs) were measured., Results: Stratified by UIC, the prevalence of hyperuricemia was 17.8%, 18.8%, 16.0% and 13.7% in the UIC < 100, 100-199, 200-299, and ≥ 300 μg/L groups, respectively; the prevalence of gout was 4.0%, 3.4%, 2.4% and 1.7%, respectively. The prevalence of gout decreased significantly as the UIC increased. The prevalence of hyperuricemia and gout were markedly higher in postmenopausal females than in the premenopausal population (hyperuricemia: 15.9% vs. 8.3%, X 2  = 520.072, p < 0.001; gout: 3.6% vs. 1.3%, X 2  = 219.889, p < 0.001), and the prevalence decreased as the UIC increased. Subjects in the more than adequate and excessive iodine groups had lower likelihoods of having hyperuricemia [aOR = 0.81 (95% CI 0.77-0.85), aOR = 0.68 (95% CI 0.64-0.72)] and lower odds of having gout than subjects in the adequate iodine (AI) group [aOR = 0.77 (95% CI 0.68-0.86), aOR = 0.59 (95% CI 0.51-0.68)]., Conclusions: UIC was inversely associated with the occurrence of hyperuricemia and gout. More in-depth research and prospective studies are needed to explore the molecular mechanisms and confirm the observed association.

Background: Iodine intake is associated with thyroid autoimmunity. In this study, we evaluated the changes in thyroid autoimmunity after 20 years of universal salt iodization (USI) in China. Methods: A total of 78,470 subjects (18 years or older) from 31 provincial regions of mainland China participated in the study. Serum thyroid peroxidase antibody (TPOAb), thyroglobulin antibody (TgAb), TSH receptor antibody, thyrotropin (TSH), and urinary iodine concentration (UIC) were measured. Results: Positive TPOAb and TgAb were detected in 10.19% [CI 9.80-10.59] and 9.70% [CI 9.28-10.13] of the subjects, respectively. The prevalence of positive isolated TPOAb (i-TPOAb), positive isolated TgAb (i-TgAb), and double positive TPOAb and TgAb (d-Ab) was 4.52%, 4.16%, and 5.94%, respectively. The prevalence of thyroid antibody positivity was the highest in the iodine-deficient (UIC <100 μg/L) groups. The prevalence of i-TPOAb was inversely associated with more than adequate iodine intake (MAI) and excessive iodine intake (EI); the odds ratio (OR) was 0.89 [CI 0.81-0.98] for MAI and 0.90 [CI 0.81-0.99] for EI. We observed that i-TgAb, like i-TPOAb, was a high-risk factor for subnormal TSH levels (OR = 3.64 [CI 2.62-5.05]) and elevated TSH levels (OR = 1.62 [CI 1.49-1.77]). The prevalence of thyroid antibody positivity varied among five ethnic groups. Conclusions: After two decades of USI, the prevalence of thyroid antibody positivity has remained low. MAI and EI had an inverse relationship with TPOAb positivity, which reveals that UIC between 100 and 299 μg/L is optimal and safe for thyroid autoimmunity. These conclusions need to be confirmed in a follow-up study because this study was a cross-sectional study.

Background: Iodine is important in both thyroid function and human metabolism. Studies have explored the effect of iodine on metabolic disorders through thyroid function. This study aimed to investigate the relationship between iodine status and metabolic disorders, such as metabolic syndrome (MetS), hypertension, impaired glucose metabolism, central obesity, and dyslipidemia. Methods: A total of 51,795 subjects aged ≥18 years from the TIDE (Thyroid Disorders, Iodine Status and Diabetes, a national epidemiological cross-sectional study) program were included. The prevalence of metabolic disorders and its related diseases was calculated based on the level of urinary iodine concentrations (UICs) using the chi-square method. To further explore whether the prevalence was associated with UIC, quadratic and UIC-stratified logistic regression models were used. Results: The prevalence of metabolic disorders as a function of UIC was found to be U-shaped with a lower prevalence of 76.0% at an UIC of 300-499 μg/L. Participants with an UIC of 300-499 μg/L showed an association with metabolic disorders (odds ratio [OR] = 0.857, 95% confidence interval [CI 0.796-0.922]) and hypertension (OR = 0.873 [CI 0.814-0.936]). An UIC of 300-799 μg/L was found to be associated with the occurrence of MetS and impaired glucose tolerance. An UIC of 500-799 μg/L was associated with the occurrence of prediabetes (OR = 0.883 [CI 0.797-0.978]). An UIC of ≥300 μg/L was associated with the occurrence of hypertriglyceridemia, hypercholesterolemia, and high levels of low-density lipoprotein cholesterol. Furthermore, an UIC of <100 μg/L showed an association with hypertension (OR = 1.097 [CI 1.035-1.162]) and hypercholesterolemia (OR = 1.178 [CI 1.117-1.242]). Conclusions: The association between UICs in adults and metabolic disorders and its related diseases is U-shaped. The association between UIC and metabolic disorders disappears in cases of iodine deficiency (<100 μg/L) or excess (≥500 μg/L).

Background: Mandatory universal salt iodization (USI) has been implemented in China for 20 years. Although iodine deficiency disorders are effectively controlled, the risk of excess iodine have been debated. Methods: A nationally representative cross-sectional study with 78,470 enrolled participants, aged 18 years or older, from all 31 provincial regions of mainland China was performed. The participants were given a questionnaire and underwent B-mode ultrasonography of the thyroid. Serum concentrations of thyroid hormones, thyroid antibodies, and urine iodine concentration (UIC) were measured. Results: The median UIC of the adult population was 177.89 μg/L. The weighted prevalence of thyroid disorders in adults were as follows: 0.78% of overt hyperthyroidism, 0.44% of subclinical hyperthyroidism, 0.53% of Graves' disease, 1.02% of overt hypothyroidism, 12.93% of subclinical hypothyroidism, 14.19% of positive thyroid antibodies, 10.19% of positive thyroid peroxidase antibodies, 9.70% of positive thyroglobulin antibodies, 1.17% of goiter, and 20.43% of thyroid nodules. Iodine excess was only associated with higher odds of overt hyperthyroidism and subclinical hypothyroidism, while iodine deficiency was significantly associated with higher odds of most thyroid disorders. In addition, increased iodine intake was significantly associated with elevated serum thyrotropin levels but was inversely associated with thyroid antibodies and thyroid nodules. Conclusions: The long-term mandatory USI program with timely adjustments is successful in preventing iodine deficiency disorders, and it appears to be safe. The benefits outweigh the risks in a population with a stable median iodine intake level of up to 300 μg/L.

Background: The goal of eliminating iodine deficiency worldwide was successfully achieved in China after the implementation of a mandatory universal salt iodization program for the last 16 years. Thus, China has been assessed as a country with more than adequate iodine levels. This survey aimed to investigate the current iodine status in China and the effects of an increased iodine intake on the spectrum and prevalence of thyroid disorders., Methods: A total of 15,008 adult subjects from 10 cities in eastern and central China were investigated. Serum thyrotropin (TSH), thyroid peroxidase antibodies (TPOAb), thyroglobulin antibodies (TgAb), and urine iodine concentration (UIC) were measured, and an ultrasonography of the thyroid was performed in all subjects. Free thyroxine (fT4) and free triiodothyronine (fT3) levels were only measured if the serum TSH was outside the normal range., Results: The median UIC values were 197 μg/L in school-age children (SAC) and 205 μg/L in a cohort population. Six cities were classified as regions with adequate iodine intake (AII), and four cities as regions with more than adequate iodine intake (MTAII), according to median SAC UIC. The prevalence of clinical hypothyroidism, subclinical hypothyroidism, and positive thyroid antibodies was significantly higher in MTAII cities than it was in AII cities. Moreover, the prevalence of clinical hyperthyroidism (1.1% vs. 0.8%, p = 0.033) and Graves' disease (0.8% vs. 0.5%, p = 0.019) also significantly increased in MTAII cities. Compared with a five-year prospective study conducted in 1999, the prevalence of goiter significantly decreased (2.9% vs. 5.02%, p = 0.001), but there was a significant increase in thyroid nodules (12.8% vs. 2.78%, p = 0.001). The prevalence of subclinical hypothyroidism (16.7% vs. 3.22%), positive TPOAb (11.5% vs. 9.81%), and positive TgAb (12.6% vs. 9.09%) significantly increased, while no changes were seen in clinical hyperthyroidism, subclinical hyperthyroidism, or Graves' disease., Conclusion: The goal of eliminating iodine deficiency has been successfully achieved in China. However, the prevalence and spectrum of thyroid disorders has increased, reflecting possible adverse effects of increased iodine intake.

Background: Hypothyroidism is a major manifestation of autoimmune thyroid diseases (AITD). We previously reported that a low selenium (Se) status was linked to an elevated prevalence of thyroid diseases. We hypothesized that Se status may also influence the restoration of thyroid function. Thus, this study aimed to investigate the factors affecting the recovery of thyroid function in patients with (sub-)clinical hypothyroidism, with a specific focus on Se status. Methods: We conducted a 6-year prospective cohort study comparing two counties with different Se concentrations. Demographic and disease data were collected from 1,190 individuals (549 Se-adequate and 641 Se-deficient) who completed a follow-up study in 2019. In addition, urinary iodine (I) levels, thyroid function, and serum and nail Se levels were measured. Logistic regression was used to investigate the relationship between Se deficiency and recovery of thyroid function. Results: Sex and smoking status was similar between the two counties studied. Thyroid function recovery rate was significantly higher in Se-deficient counties (46.0% vs. 30.6%, P = 0.008). In the multivariate analysis, our results show that female sex (odds ratio [OR] (95% confidence interval [CI]) = 1.875 (1.080–3.257), P = 0.026] and increasing age [OR (95%CI) = 1.028(1.007–1.049), P = 0.009] were associated with the recovery rate. Additionally, our study revealed that while Se status was significant in the univariate analysis, this association appeared to disappear in the multivariate analysis. Conclusions: Female sex and increasing age have unfavorable effects on the recovery of thyroid function in patients over 30 years of age with (sub-) clinical hypothyroidism. [ABSTRACT FROM AUTHOR]