Prolonged high iodine intake is associated with inhibition of type 2 deiodinase activity in pituitary and elevation of serum thyrotropin levels

The correlation between iodine and metabolism: a review

Iodine is involved in the synthesis of thyroid hormones and plays a crucial role in human life. Both iodine deficiency and excess are common issues in certain populations. Iodine also has extrathyroidal effects on organs that can uptake it independently of thyroid hormones. Recently, multiple clinical studies have shown a connection between iodine intake and metabolic disorders, such as metabolic syndrome, obesity, diabetes, hypertension, and dyslipidemia. However, the results of these studies have been inconsistent, and the mechanisms behind these associations are still not well understood. Therefore, in this review, we aim to examine the recent research progress regarding the relationship between iodine and metabolic disorders, along with the relevant mechanisms.

Mechanism of multi-organ compensation under different iodine intake in pregnant rats: results from a repeated-measures study of iodine metabolism

PURPOSE

This study aimed to explore the differences in iodine metabolism and expression of NIS and Pendrin in pregnant rats under different iodine nutritional status.

METHODS

Female Wistar rats were divided into four groups: low iodine (LI), normal iodine (NI), ten fold high iodine (10HI), and fifty fold high iodine (50HI). The intervention began after one week of adaptive feeding. Iodine metabolism experiments were performed beginning on the 15th day of pregnancy. 24-h iodine intake and excretion were calculated. The concentrations of iodine in urine, fecal, thyroid, and placenta were measured by ICP-MS. PCR and Western Blot were used to detect the mRNA levels and cell membrane protein of sodium/iodide symporter (NIS) and Pendrin in the small intestine, thyroid, kidney, and placenta.

RESULTS

Fecal iodine excretion (FIE) and urinary iodine excretion (UIE) in the 50HI group were significantly higher than those in the NI group (P < 0.05). The NIS protein and mRNA in the kidney and small intestine have an upward trend in iodine deficiency and a downward trend in iodine excess. Thyroid and placental iodine storage in the 50HI group were significantly higher than those in the NI group (P < 0.05). NIS, Pendrin protein, and mRNA in the thyroid and placenta tend to increase when iodine is deficient and decrease when there is excess.

CONCLUSION

Iodine excretion and iodine stores in the placenta and thyroid gland are positively correlated with iodine intake. NIS and Pendrin are also regulated by iodine intake.

The Role of Thyroid Hormone Synthesis Gene-Related miRNAs Profiling in Structural and Functional Changes of The Thyroid Gland Induced by Excess Iodine

At recent years, the impairment caused by iodine excess are paid more attention. However, there is still largely unknown about the exact mechanism induced by excessive iodine. MiRNAs have been found to act as biomarkers for a variety of diseases, whereas fewer studies focused on miRNAs related to a cluster of genes regulating thyroid hormone synthesis, such as NIS, Pendrin, TPO, MCT8, TSHR, TSHα, and TSHβ-related miRNAs in structural and functional changes of the thyroid gland induced by subchronic and chronic high iodine exposure. In the present study, one hundred and twenty 4-week-old female Wistar rats were randomly divided into control group (I50µg/L KIO3); HI 1 (I6000µg/L KIO3); HI 2 (I10000µg/L KIO3); and HI 3 (I50000µg/L KIO3), the exposure period was 3 months and 6 months, respectively. The iodine contents in the urine and blood, thyroid function, and pathological changes were determined. In addition, levels of thyroid hormone synthesis genes and the associated miRNAs profiling were detected. The results showed that subclinical hypothyroidism occurred in the high iodine groups with subchronic high iodine exposure, while 6-month exposure led to hypothyroidism in the I10000µg/L and I50000µg/L groups. Subchronic and chronic high iodine exposure caused mRNA and protein levels of NIS, TPO, and TSHR decreased significantly, and Pendrin expression increased significantly. In addition, MCT8 mRNA and protein levels are only remarkably decreased under the subchronic exposure. PCR results showed that levels of miR-200b-3p, miR-185-5p, miR-24-3p, miR-200a-3p, and miR-25-3p increased significantly exposed to high iodine for 3 months, while miR-675-5p, miR-883-5p, and miR-300-3p levels increased significantly under the exposure to high iodine for 6 months. In addition, miR-1839-3p level was markedly decreased exposed to high iodine for 3 and 6 months. Taken together, the miRNA profiling of genes regulating thyroid hormone synthesis remarkably altered from subclinical hypothyroidism to hypothyroidism induced by excess iodine exposure, and some miRNAs may play an important role in subclinical hypothyroidism or hypothyroidism through regulating NIS, Pendrin, TPO, MCT8, and TSHR providing promising targets to alleviate the impairment on the structure and function of thyroid gland.

What are the risks associated with lipiodol hysterosalpingography? A literature review

INTRODUCTION

Hysterosalpingography is widely used as a first-line investigation for infertility, and may also be therapeutic, increasing pregnancy rates. Aqueous and oil-based contrast agents can be used. Some studies suggest Lipiodol hysterosalpingography has a greater therapeutic effect on fertility than aqueous contrast, though this is contentious. There are additionally safety concerns surrounding Lipiodol hysterosalpingography. This review summarises the adverse effects associated with Lipiodol hysterosalpingography, particularly on thyroid function.

KEY FINDINGS

331 articles were identified. Of these, 46 met inclusion criteria. 3 further articles were identified from reference lists. Complications typically cited in the literature include pain, intravasation, life-threatening oil embolism, and lipogranuloma formation. Emerging evidence suggests that Lipiodol hysterosalpingography may also impact maternal and neonatal thyroid function. Women may develop hypo- or hyperthyroidism. Thyroid dysfunction is clinically significant as even subclinical hypothyroidism reduces fertility, increases the risk of pregnancy complications including miscarriage, pre-eclampsia and perinatal mortality, and adversely impacts foetal neurodevelopment. One study suggested a possible link with neonatal congenital hypothyroidism.

CONCLUSION

There is emerging evidence to suggest that Lipiodol hysterosalpingography can cause hypo- or hyperthyroidism, in addition to known adverse effects of pain, intravasation, oil embolism, and lipogranuloma formation.

IMPLICATIONS FOR PRACTICE

Given the significance of these risks, and contention surrounding whether Lipiodol truly increases pregnancy rates compared to aqueous mediums, careful consideration is required in the selection of contrast agent. In particular, Lipiodol hysterosalpingography may not be suitable for women with pre-existing thyroid dysfunction.

Prevalence and risk factors of hypothyroidism after universal salt iodisation: a large cross-sectional study from 31 provinces of China

OBJECTIVES

To investigate the prevalence and risk factors of hypothyroidism after universal salt iodisation for 20 years in mainland China.

DESIGN

Nationwide, cross-sectional survey.

SETTING AND PARTICIPANTS

The Thyroid Disorders, Iodine Status and Diabetes epidemiological study included adults from 31 provinces of China. Data included demographic, physical characteristics, urine, serum thyroid-stimulating hormone (TSH), thyroid-peroxidase antibody (TPOAb), thyroglobulin antibody (TgAb) and thyroid ultrasonography. Subclinical hypothyroidism (SCH) was classified into severe SCH (TSH >10 mU/L) and mild SCH (TSH 4.2-9.9 mU/L). A total of 78 470 (38 182 men and 40 288 women) participants were included in the final analysis.

RESULTS

The prevalence of hypothyroidism was 13.95%. The prevalence rates of overt hypothyroidism (OH) and SCH were 1.02% and 13.93%, which mild SCH was significantly higher than severe SCH (12.18% vs 0.75%). Prevalence was higher in women than in men, and this gender difference was noted among all age groups. The prevalence of mild SCH, severe SCH and OH increases by 1.16%, 1.40% and 1.29% for every 10 years older. TPOAb or/and TgAb positive were significantly associated with OH and severe SCH (OR 15.9, p<0.001). However, SCH was positively correlated with increased urine iodine concentration, but this correlation was only in antibody-negative female patients. In non-autoimmune and male populations, there was a U-shaped relationship between severe SCH and OH and urine iodine concentration.

CONCLUSIONS

Mild SCH is the most common form of hypothyroidism, which is related to iodine intake. Severe SCH is more similar to OH which autoimmune is the main cause. The various effects of iodine on hypothyroidism depend on thyroid autoimmune and gender.

Deficiency and excess of groundwater iodine and their health associations

More than two billion people worldwide have suffered thyroid disorders from either iodine deficiency or excess. By creating the national map of groundwater iodine throughout China, we reveal the spatial responses of diverse health risks to iodine in continental groundwater. Greater non-carcinogenic risks relevant to lower iodine more likely occur in the areas of higher altitude, while those associated with high groundwater iodine are concentrated in the areas suffered from transgressions enhanced by land over-use and intensive anthropogenic overexploitation. The potential roles of groundwater iodine species are also explored: iodide might be associated with subclinical hypothyroidism particularly in higher iodine regions, whereas iodate impacts on thyroid risks in presence of universal salt iodization exhibit high uncertainties in lower iodine regions. This implies that accurate iodine supply depending on spatial heterogeneity and dietary iodine structure optimization are highly needed to mitigate thyroid risks in iodine-deficient and -excess areas globally.

The SELFI Study: Iodine Excess and Thyroid Dysfunction in Women Undergoing Oil-Soluble Contrast Hysterosalpingography

CONTEXT

Hysterosalpingography (HSG) with oil-soluble contrast medium (OSCM) improves pregnancy rates. However, OSCM has high iodine content and long half-life, leading to potential iodine excess.

OBJECTIVE

This work aimed to determine the pattern of iodine excess after OSCM HSG and the effect on thyroid function.

METHODS

A prospective cohort study was conducted of 196 consecutive consenting eligible women without overt hypothyroidism or hyperthyroidism. All completed the study with compliance greater than 95%. Participants underwent OSCM HSG (Auckland, 2019-2021) with serial monitoring of thyrotropin (TSH), free thyroxine (FT4), and urine iodine concentration (UIC) for 24 weeks. The main outcome measure was the development of subclinical hypothyroidism (SCH), defined as a nonpregnant TSH greater than 4 mIU/L with normal FT4 (11-22 pmol/L) in those with normal baseline thyroid function.

RESULTS

Iodine excess (UIC ≥ 300 μg/L) was almost universal (98%) with UIC peaking usually by 4 weeks. There was marked iodine excess, with 90% and 17% of participants having UIC greater than or equal to 1000 μg/L and greater than 10 000 μg/L, respectively. Iodine excess was prolonged with 67% having a UIC greater than or equal to 1000 μg/L for at least 3 months. SCH developed in 38%; the majority (96%) were mild (TSH 4-10 mIU/L) and most developed SCH by week 4 (75%). Three participants met the current treatment guidelines (TSH > 10 mIU/L). Thyroxine treatment of mild SCH tended to improve pregnancy success (P = .063). Hyperthyroidism (TSH < 0.3 mIU/L) occurred in 9 participants (5%).

CONCLUSION

OSCM HSG resulted in marked and prolonged iodine excess. SCH occurred frequently with late-onset hyperthyroidism occasionally. Regular thyroid function tests are required for 6 months following this procedure.

Association Between Blood Pressure, Glomerular Filtration Rate, and Serum Thyroid-Stimulating Hormone Levels in Hypothyroid Patients: A Retrospective Single-Center Study

Background: Thyroid hormones have substantial effects on blood pressure (BP) and renal function as they influence the glomerular filtration rate (GFR). Maintaining healthy BP and preventing premature development of nephropathy necessitates taking steps.

Objectives: The aim of this study was to explore the association between BP, GFR, and thyroid-stimulating hormone (TSH) levels in hypothyroid patients at King Abdulaziz University Hospital, Jeddah, Saudi Arabia.

Methods: A retrospective record review study of all hypothyroid patients from June 1, 2010 to June 6, 2020. The medical records of 1,181 adult patients were reviewed, and 157 met the criteria. All patients aged >18 years who were diagnosed with hypothyroidism and were on levothyroxine therapy, were included in this study.

Results: More than half of the participants were female (83.4%). There was no significant correlation between TSH and systolic BP (P= 0.6), or TSH and diastolic BP (P=0.8), while there was a positive correlation between TSH and creatinine (r=0.4, P=0.001) and a negative correlation between TSH and GFR (r=−0.2, P=0.01).

Conclusions: We found no association between BP and TSH, while creatinine correlated directly and GFR inversely with TSH. Follow-up renal function should be a target for physicians in hypothyroid patients to prevent premature complications.

Effects of iodine excess on serum thyrotropin-releasing hormone levels and type 2 deiodinase in the hypothalamus of Wistar rats

Iodine is an important element in thyroid hormone biosynthesis. Thyroid function is regulated by the hypothalamic-pituitary-thyroid axis. Excessive iodine leads to elevated thyroid-stimulating hormone (TSH) levels, but the mechanism is not yet clear. Type 2 deiodinase (Dio2) is a Se-containing protease that plays a vital role in thyroid function. The purpose of this study was to explore the role of hypothalamus Dio2 in regulating TSH increase caused by excessive iodine and to determine the effects of iodine excess on thyrotropin-releasing hormone (TRH) levels. Male Wistar rats were randomised into five groups and administered different iodine dosages (folds of physiological dose): normal iodine, 3-fold iodine, 6-fold iodine, 10-fold iodine and 50-fold iodine. Rats were euthanised at 4, 8, 12 or 24 weeks after iodine administration. Serum TRH, TSH, total thyroxine (TT4) and total triiodothyronine (TT3) were determined. Hypothalamus tissues were frozen and sectioned to evaluate the expression of Dio2, Dio2 activity and monocarboxylate transporter 8 (MCT8). Prolonged high iodine intake significantly increased TSH expression (P < 0·05) but did not affect TT3 and TT4 levels. Prolonged high iodine intake decreased serum TRH levels in the hypothalamus (P < 0·05). Dio2 expression and activity in the hypothalamus exhibited an increasing trend compared at each time point with increasing iodine intake (P < 0·05). Hypothalamic MCT8 expression was increased in rats with prolonged high iodine intake (P < 0·05). These results indicate that iodine excess affects the levels of Dio2, TRH and MCT8 in the hypothalamus.

Associations of urinary perchlorate, nitrate and thiocyanate with central sensitivity to thyroid hormones: A US population-based cross-sectional study

BACKGROUND

Perchlorate, nitrate, and thiocyanate are three well-known sodium iodine symporter inhibitors, however, associations of their individual and concurrent exposure with central thyroid hormones sensitivity remain unclear.

OBJECTIVES

To investigate the associations of urinary perchlorate, nitrate, thiocyanate, and their co-occurrence with central thyroid hormones sensitivity among US general adults.

METHODS

A total of 7598 non-pregnant adults (weighted mean age 45.9 years and 52.9% men) from National Health and Nutritional Examination Survey 2007-2012 were included in this cross-sectional study. Central sensitivity to thyroid hormones was estimated with the Parametric Thyroid Feedback Quantile-based Index (PTFQI). Ordinary least-squares regression, weighted quantile sum (WQS) regression, and Bayesian kernel machine regression (BKMR) models were performed to examine the associations of three anions and their co-occurrence with PTFQI.

RESULTS

The weighted mean values of urinary perchlorate, nitrate, thiocyanate, and perchlorate equivalent concentration (PEC) were 5.48 μg/L, 57.59 mg/L, 2.65 mg/L, and 539.8 μg/L, respectively. Compared with the lowest quartile, the least-square means difference (LSMD) of PTFQI was -0.0516 (LSMD ± SE: -0.0516 ± 0.0185, P < 0.01) in the highest perchlorate quartile. On average, PTFQI decreased by 0.0793 (LSMD ± SE: -0.0793 ± 0.0205, P < 0.001) between the highest and lowest thiocyanate quartile. Compared with those in the lowest quartile, participants in the highest PEC quartile had significantly decreased PTFQI levels (LSMD ± SE: -0.0862 ± 0.0188, P < 0.001). The WQS of three goitrogens, was inversely associated with PTFQI (β: -0.051, 95% CI: -0.068, -0.034). In BKMR model, PTFQI significantly decreased when the levels of three anions were at or above their 60th percentiles compared to the median values.

CONCLUSIONS

Higher levels of urinary perchlorate, thiocyanate, and co-occurrence of three goitrogens were associated with increased central thyroid hormones sensitivity among US general adults. Further studies are warranted to replicate our results and elucidate the underlying causative mechanistic links.

[Epidemiology of benign thyroid disorders in the adult population of the Republic of Belarus: analysis of nationwide statistics 2009 to 2019]

BACKGROUND

Nowadays, the Republic of Belarus belongs to the countries with sufficient iodine supply, which made it possible to reduce the incidence of non-toxic goiter and congenital hypothyroidism. However, even a slight change in iodine consumption influences the pattern of thyroid diseases. In addition to iodine deficiency, other environmental conditions, as well as genetic factors, play a significant role in the etiology of thyroid diseases.

AIM

To analyze the dynamics of the main epidemiological indicators of benign thyroid diseases from 2009 to 2019 in the adult population of the Republic of Belarus, using the data of official state statistics.

MATERIALS AND METHODS

The indicators of the incidence and prevalence of benign thyroid diseases were studied on the basis of state statistics for 2009-2019. To analyze the dynamics of the studied indicators, regression analysis was used with the construction of linear and polynomial models.

RESULTS

A decrease in the incidence and prevalence of diffuse euthyroid goiter and an increase in the incidence and prevalence of nodular euthyroid goiter, thyroiditis, acquired hypothyroidism, Graves' disease, as well as the incidence of nodular toxic goiter were revealed.

CONCLUSION

Obtained data indicate, that there is an increase in the prevalence of most of the studied thyroid diseases, despite the adequate iodine supply. The above justifies the need for further study of the causes of the identified trends, as well as the necessity of developing new methods of diagnosis and treatment of thyroid diseases.

The Status of Iodine Nutrition after Removing Iodized Salt in High Water Iodine Regions: a Cross-sectional Study in China

Currently, the removal of iodized salt is carried out in high water iodine regions. The present situation of iodine nutrition and the prevalence of thyroid diseases in such regions have not been clearly elucidated. This study aimed to figure out these problems to help render effective measures for cases of abnormal iodine nutrition status. A cross-sectional study was carried out in four areas of Jining and Heze, Shandong Province, China, with different water iodine concentrations (WIC). In total, 1344 adults were enrolled in this study, and data related to their iodine nutrition, thyroid function, and thyroid ultrasonography were collected. Subjects were grouped according to WIC, urine iodine concentration (UIC), serum iodine concentration (SIC), and combined UIC and SIC for analysis. Iodine levels were in excess in the 100 μg/L ≤ WIC < 300 μg/L and WIC ≥ 300 μg/L areas. Compared with the control WIC group (10-100 μg/L), the WIC ≥ 300 μg/L group had a higher prevalence of thyroid autoimmunity (TAI, 21.25% vs. 13.19%, P <0.05), subclinical hypothyroidism (SH, 20.20% vs. 11.96%, P < 0.05), thyroid nodules (TN, 31.75% vs. 18.71%, P < 0.05), and thyroid dysfunction (23.62% vs. 12.26%, P < 0.05). Compared with the UIC control group (100-300 μg/L), high UIC group (≥ 800 μg/L) had a higher prevalence of TN (33.75% vs. 21.14%, P < 0.05) and thyroid dysfunction (25% vs. 14.47%, P < 0.05). Next, compared with the control SIC group (50-110 μg/L), high SIC group (≥ 110 μg/L) had a higher prevalence of TAI (33.80% vs. 14.47%, P < 0.05), SH (23.94% vs. 14.30%, P < 0.05), and thyroid dysfunction (33.80% vs. 15.29%, P < 0.05). Finally, subjects with the highest UIC and the highest SIC also had a higher prevalence of TAI (25.92% vs. 10.97%, P < 0.05), SH (23.45% vs. 10.97%, P < 0.05), TN (34.56% vs. 15.85%, P < 0.05), and thyroid dysfunction (27.16% vs. 13.41%, P < 0.05) than subjects with middle iodine levels. The iodine nutrition of subjects in the WIC ≥ 300 μg/L areas was still in excess after removing iodized salt from their diets. High levels of iodine also increased the prevalence of TAI, SH, TN, and thyroid dysfunction in those areas. Simply removing iodized salt may not be sufficient for high water iodine regions.

Association between Iodine Intake, Thyroid Function, and Papillary Thyroid Cancer: A Case-Control Study

BACKGROUND

This study aimed to assess the effects of iodine intake, thyroid function, and their combined effect on the risk of papillary thyroid cancer (PTC) and papillary thyroid microcarcinoma (PTMC).

METHODS

A case-control study was conducted including 500 community-based controls who had undergone a health check-up, and 446 overall PTC cases (209 PTC and 237 PTMC) from the Thyroid Cancer Longitudinal Study. Urinary iodine concentration (UIC), was used as an indicator of iodine intake, and serum for thyroid function. The risk of PTC and PTMC was estimated using unconditional logistic regression.

RESULTS

Excessive iodine intake (UIC ≥220 μg/gCr) was associated with both PTC (odds ratio [OR], 18.13 95% confidence interval [CI], 8.87 to 37.04) and PTMC (OR, 8.02; 95% CI, 4.64 to 13.87), compared to adequate iodine intake (UIC, 85 to 219 μg/gCr). Free thyroxine (T4) levels ≥1.25 ng/dL were associated with PTC (OR, 1.97; 95% CI, 1.36 to 2.87) and PTMC (OR, 2.98; 95% CI, 2.01 to 4.41), compared to free T4 levels of 0.7 to 1.24 ng/dL. Individuals with excessive iodine intake and high free T4 levels had a greatly increased OR of PTC (OR, 43.48; 95% CI, 12.63 to 149.62), and PTMC (OR, 26.96; 95% CI, 10.26 to 70.89), compared to individuals with adequate iodine intake and low free T4 levels.

CONCLUSION

Excessive iodine intake using creatinine-adjusted UIC and high free T4 levels may have a synergistic effect on PTC and PTMC. Considering both iodine intake and thyroid function is important to assess PTC and PTMC risk.

Distributions of serum thyroid-stimulating hormone in 2020 thyroid disease-free adults from areas with different iodine levels: a cross-sectional survey in China

PURPOSE

The aim of the present study was to describe the distributions of serum thyroid- stimulating hormone (TSH) levels in thyroid disease-free adults from areas with different iodine levels in China. Meanwhile, we aimed to evaluate the influence of age and gender on the distribution of TSH, assess the relationship between concentrations of TSH and free thyroxine (FT₄), and analyze the factors that may affect TSH levels.

METHODS

2020 adults were included from April 2016 to June 2019. Urinary iodine concentration, serum iodine concentration, serum TSH, FT₄, free triiodothyronine, thyroid peroxidase antibodies and thyroglobulin antibodies were measured, and thyroid ultrasonography was performed.

RESULTS

The median of TSH in iodine-fortification areas (IFA), iodine-adequate areas (IAA), iodine-excessive areas (IEA) were 2.32, 2.11 and 2.34 mIU/L, respectively. Serum TSH concentrations were significantly higher in IFA and IEA than that in IAA (p = 0.005 and < 0.0001). The TSH values of most adults were distributed within the range of 1.01-3.00 mIU/L with the same trend in three groups. In our study, TSH levels did not change with age, and the TSH level of females was higher than that of males (p < 0.0001). There was a negative correlation between FT₄ and TSH in IAA (r = - 0.160, p < 0.0001) and IEA (r = - 0.177, p < 0.0001), but there was no correlation between FT₄ and TSH in IFA (r = - 0.046, p = 0.370). BMI, smoking status, education levels, and marital status were associated with TSH.

CONCLUSION

Our study provides a basis for establishing the reference intervals of TSH in different iodine level areas.

Evaluation and Treatment of Amiodarone-Induced Thyroid Disorders

Amiodarone is a class III antiarrhythmic drug containing 37% iodine by weight, with a structure similar to that of thyroid hormones. Deiodination of amiodarone releases large amounts of iodine that can impair thyroid function, causing either hypothyroidism or thyrotoxicosis in susceptible individuals reflecting ~20% of patients administered the drug. Not only the excess iodine, but also the amiodarone (or its metabolite, desethylamiodarone) itself may cause thyroid dysfunction by direct cytotoxicity on thyroid cells. We present an overview of the epidemiology and pathophysiology of amiodarone-induced thyroid disorders, with a focus on the various forms of clinical presentation and recommendations for personalized management of each form.

The Effect of Increased Iodine Intake on Serum Thyrotropin: A Cross-Sectional, Chinese Nationwide Study

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.

Efficacy and Safety of Long-Term Universal Salt Iodization on Thyroid Disorders: Epidemiological Evidence from 31 Provinces of Mainland China

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.

Prevalence and clinical correlates of subclinical hypothyroidism in first-episode drug-naive patients with major depressive disorder in a large sample of Chinese

BACKGROUND

The coexistence of subclinical hypothyroidism (SCH) and depression has been intensively examined in the patients receiving thyroxine or antidepressant treatment. This study aimed to investigate the prevalence and clinical correlates of severe SCH in Chinese first-episode drug naïve patients with major depressive disorder (MDD).

METHODS

Using a cross-sectional design, we recruited a total of 1706 MDD patients. Depressive symptoms were evaluated using the 17-item Hamilton Depression Rating Scale (HAMD). Severity of anxiety and psychiatric symptoms were evaluated by the Hamilton Anxiety Rating Scale (HAMA) and the Positive and Negative Syndrome Scale (PANSS), respectively. Serum thyroid function parameters were measured by a chemiluminescence immunoassay. Based on the serum thyroid stimulating hormone (TSH) level, SCH was further divided into mild (TSH < 10 mIU/L) and severe SCH (TSH ≥ 10 mIU/L).

RESULTS

More patients with severe SCH had severe anxiety, psychotic symptoms, suicide attempts (all p < 0.001), compared with those without severe SCH. Logistic regression showed that suicide attempts and psychiatric symptoms were associated with severe SCH (both p < 0.001). Multiple linear regression showed that age (p < 0.05), BMI (p < 0.001), HAMD score (p < 0.001), HAMA score (p < 0.001), PANSS positive subscore (p = 0.001) and CGI score (p = 0.001) were associated with TSH levels.

CONCLUSION

Our findings suggest that suicide attempts and psychiatric symptoms may be associated with severe SCH. Moreover, severe anxiety, depressive and psychotic symptoms, as well as older age and higher BMI are possibly related to elevated TSH levels.

The Association of Maternal Iodine Status in Early Pregnancy with Thyroid Function in the Swedish Environmental Longitudinal, Mother and Child, Asthma and Allergy Study

Background: Severe maternal iodine deficiency can impact fetal brain development through effects on maternal and/or fetal thyroid hormone availability. The effects of mild-to-moderate iodine deficiency on thyroid function are less clear. The aim was to investigate the association of maternal urinary iodine concentration corrected for creatinine (UI/Creat) with thyroid function and autoantibodies in a mild-to-moderate iodine-deficient pregnant population. Methods: This study was embedded within the Swedish Environmental Longitudinal, Mother and child, Asthma and allergy (SELMA) study. Clinical reference ranges were determined by the 2.5th and 97.5th population-based percentile cutoffs. The associations of UI/Creat with thyrotropin (TSH), free thyroxine (fT4), free triiodothyronine (fT3), total T4 (TT4), and total T3 (TT3) were studied using multivariable linear regression in thyroid peroxidase antibody (TPOAb)-negative women. The association of UI/Creat with TPOAb and thyroglobulin antibody (TgAb) positivity was analyzed using multivariable logistic regression. Results: Urinary iodine and thyroid function were measured at a median (95% range) gestational age of 10 (6-14) weeks in 2009 women. The median (95% range) UI/Creat was 85 μg/g (36-386) and the UI/Creat was below 150 μg/g in 80.1% of women. Reference ranges did not differ substantially by UI/Creat. A lower UI/Creat was associated with a lower TSH (p = 0.027), a higher TT4 (p = 0.032), and with a corresponding trend toward slightly higher fT4 (p = 0.081), fT3 (p = 0.079), and TT3 (p = 0.10). UI/Creat was not associated with the fT4/fT3 (p = 0.94) or TT4/TT3 ratios (p = 0.63). Women with a UI/Creat of 150-249 μg/g had the lowest prevalence of TPOAb positivity (6.1%), while women with a UI/Creat of <150 μg/g had a higher prevalence (11.0%, odds ratio [OR] confidence interval [95% CI] 1.84 [1.07-3.20], p = 0.029). Women with a UI/Creat ≥500 μg/g showed the highest prevalence and a higher risk of TPOAb positivity, however, only a small proportion of women had such a UI/Creat (12.5%, OR, [95% CI] 2.36 [0.54-10.43], p = 0.26). Conclusions: We could not identify any meaningful differences in thyroid function reference ranges. Lower iodine availability was associated with a slightly lower TSH and a higher TT4. Women with adequate iodine intake had the lowest risk of TPOAb positivity.

Reference Range and Sociodemographic Characteristics of TSH among Reproductive Age Women in Rural China

Appropriate reference range of thyroid-stimulating hormone (TSH) is important to interpreting the results of thyroid functional tests. However, the reference range and sociodemographic characteristics of TSH based on large-scale studies are yet to be declared in rural China. To clarify reference range and sociodemographic characteristics of TSH in reproductive age of women from rural China. A nationwide population-based study was conducted as The National Free Preconception Health Examination Project (NFPHEP). Nearly 400,000 (n = 392,659) of Chinese rural women aged 15-55 years were randomly recruited. Predetermined strict exclusion criteria made a number of 359,895 as the reference population. Serum TSH was evaluated with enzyme-linked immunosorbent assay (ELISA). The reference range of TSH on overall and reference population was 0.39-5.20 and 0.39-5.13 uIU/ml (2.5th-97.5th percentiles), respectively. In the reference population, the range (2.5th to 97.5th percentile) of serum TSH in different age groups was 0.40-5.03 uIU/ml, 0.39-5.15 uIU/ml, 0.37-6.10 uIU/ml, and 0.44-7.03 uIU/ml, respectively. The mean TSH value in women aged 26-35 years was 2.26 uIU/ml, significantly lower than those aged 36-45 (p < 0.001). The mean TSH values for eastern, central, and western regions were 2.28 uIU/ml, 2.29 uIU/ml, and 2.24 uIU/ml respectively. The mean of serum TSH concentration was significantly higher in central region than that in western region (p ≤ 0.001). The TSH value 0.39-5.13 uIU/ml (2.5th-97.5th percentiles) was derived as a reference range of reproductive age women from rural China. We use the TSH ranges from reference population to diagnose hyperthyrotropinemia or hypothyroidism in different areas in China. The reference ranges for eastern, central, and western regions were 0.33-5.61 uIU/ml, 0.40-5.04 uIU/ml, and 0.40-4.98 uIU/ml (2.5th-97.5th percentiles) respectively. The value of serum TSH was associated with age, living region, smoking, drinking, educational level, and interpersonal tension, as well as life and economic pressure, but irrelevant to ethnicity or occupation.

Association of TSHR Gene Copy Number Variation with TSH Abnormalities

Thyroid-stimulating hormone (TSH) is secreted by the pituitary gland and promotes thyroid growth and function, with increased TSH levels typically associated with hypothyroidism. By consulting the literature, we found that the TSHR, PAX8, and PDE4B genes are associated with thyroid function. Recently, copy number variations (CNVs) have been used as genetic markers to investigate inter-individual variation. Therefore, we investigated the relationship between the TSHR, PAX8, and PDE4B gene CNVs and TSH abnormalities, by calculating variations in gene copy number. Four hundred and eighty-one participants, 232 healthy controls and 249 patients with TSH abnormalities, were selected from three distinct areas in China with different iodine statuses. RT-PCR was used to detect CNVs. Urinary iodine concentrations (UIC) were measured by As³⁺-Ce⁴⁺ catalytic spectrophotometry. There was an association between a CNV at the TSHR gene and TSH abnormalities (p = 0.002). The distribution of PAX8 and PDE4B gene CNVs between patients with TSH abnormalities and healthy controls was not significantly different. UIC > 200 μg/l (OR = 1.49, 95% CI = 1.01-2.22) and the TSHR gene (OR = 6.01, 95% CI = 1.96-18.41) were found to be risk factors for TSH abnormalities. PAX8 and PDE4B gene CNVs were not significantly associated with TSH abnormalities. There was no significant interaction between UIC and any of the examined CNVs. In conclusion, the TSHR gene CNV was associated with the development of TSH abnormalities. No significant associations were revealed between urinary iodine levels and candidate gene CNVs.

Nitric oxide is involved in the hypothyroidism with significant morphology changes in female Wistar rats induced by chronic exposure to high water iodine from potassium iodate

Epidemiological studies indicated that chronic exposure to high water iodine is associated with primary hypothyroidism (PH) and subclinical hypothyroidism (SCH). However, the mechanism is not well understood. In this study, we explored whether chronic exposure to high water iodine from potassium iodate (KIO₃) can induce hypothyroidism in addition to determining if nitric oxide (NO) is involved in the pathogenesis. 96 female Wistar rats were divided into six groups: control, I_1000μg/L, I_3000μg/L, I_6000μg/L, N-nitro-L-arginine methylester (L-NAME) and L-NAME+I_6000μg/L. After 3 months, urine iodine concentration, thyroid hormone, NO and nitric oxide synthase (NOS) serum levels were determined. Additionally, thyroid expression of inducible nitric oxide synthase (iNOS) was also investigated. Thyroid morphology was observed under light microscopy and transmission electron microscope. SCH as indicated by elevated serum thyrotropin (TSH) was induced among rats exposed to 3000 μg/L I^-, while rats treated with 6000 μg/L I^- presented PH characterized by elevated TSH and lowered total thyroxine in serum. Moreover, serum NO, NOS and iNOS expression in the thyroid were significantly increased in I_3000μg/L and I_6000μg/L groups. Changes in thyroid function and morphology in the L-NAME+I_6000μg/L group were extenuated compared to I_6000μg/L group. These findings suggested that chronic exposure to high water iodine from KIO₃ likely induces hypothyroidism with significant morphology changes in female Wistar rats and NO appears to be involved in the pathogenesis.

High Urinary Iodine, Thyroid Autoantibodies, and Thyroid-Stimulating Hormone for Papillary Thyroid Cancer Risk

Thyroid nodules have become a common clinical problem, and the clinical importance of thyroid nodules lies in the determination of thyroid cancer. This study aims to evaluate the risk factors for papillary thyroid cancer (PTC) with regard to urinary iodine concentration (UIC), thyroid-stimulating hormone (TSH), thyroid peroxidase antibody (TPOAb), and thyroglobulin antibody (TGAb) in comparison to thyroid nodular goiter (NG). Among the 2041 patients, 43.8% of which showed more than adequate (UIC 200-299 μg/L) and excessive iodine (UIC ≥ 300.0 μg/L) status. Compared with adequate iodine intake, iodine deficiency (UIC < 100 μg/L) was inversely associated with multifocality (OR 0.59, P = 0.040), while more than adequate iodine intake was independently associated with an increased risk of larger tumor size (OR 1.33, P = 0.002) in female PTC patients but not in males. No significant difference in UIC was observed between patients with PTC and NG, suggesting that high iodine intake may be related with the growth of PTC, but not with its oncogenesis. Besides, positive for TPOAb and TGAb were individually associated with papillary thyroid microcarcinoma (PTMC) risk (OR 2.05 and 1.71, respectively, both P < 0.05) in female patients with tumor foci < 1 cm but not in males. Furthermore, younger age (< 46 years), TGAb positivity and small thyroid nodules in both sexes, higher TSH, TPOAb positivity, and multifocality in females could all predict PTC risk (all P < 0.05). These results might have clinical significance for managing patients with thyroid nodules and those with thyroidectomy.

Maternal Exposure to Iodine Excess Throughout Pregnancy and Lactation Induces Hypothyroidism in Adult Male Rat Offspring

This study aimed to investigate the consequences of maternal exposure to iodine excess (IE; 0.6 mg NaI/L) throughout pregnancy and lactation on the hypothalamus-pituitary-thyroid axis of the male offspring in adulthood. Maternal IE exposure increased hypothalamic Trh mRNA expression and pituitary Tsh expression and secretion in the adult male offspring. Moreover, the IE-exposed offspring rats presented reduced thyroid hormones levels, morphological alterations in the thyroid follicles, increased thyroid oxidative stress and decreased expression of thyroid differentiation markers (Tshr, Nis, Tg, Tpo, Mct8) and thyroid transcription factors (Nkx2.1, Pax8). Finally, the data presented here strongly suggest that epigenetic mechanisms, as increased DNA methylation, augmented DNA methyltransferases expression, hypermethylation of histone H3, hypoaceylation of histones H3 and H4, increased expression/activity of histone deacetylases and decreased expression/activity of histone acetyltransferases are involved in the repression of thyroid gene expression in the adult male offspring. In conclusion, our results indicate that rat dams' exposure to IE during pregnancy and lactation induces primary hypothyroidism and triggers several epigenetic changes in the thyroid gland of their male offspring in adulthood.

Iodine excess exposure during pregnancy and lactation impairs maternal thyroid function in rats

Adequate maternal iodine consumption during pregnancy and lactation guarantees normal thyroid hormones (TH) production, which is crucial to the development of the fetus. Indeed, iodine deficiency is clearly related to maternal hypothyroidism and deleterious effects in the fetal development. Conversely, the effects of iodine excess (IE) consumption on maternal thyroid function are still controversial. Therefore, this study aimed to investigate the impact of IE exposure during pregnancy and lactation periods on maternal hypothalamus-pituitary-thyroid axis. IE-exposed dams presented reduced serum TH concentration and increased serum thyrotropin (TSH) levels. Moreover, maternal IE exposure increased the hypothalamic expression of Trh and the pituitary expression of Trhr, Dio2, Tsha and Tshb mRNA, while reduced the Gh mRNA content. Additionally, IE-exposed dams presented thyroid morphological alterations, increased thyroid oxidative stress and decreased expression of thyroid genes/proteins involved in TH synthesis, secretion and metabolism. Furthermore, Dio1 mRNA expression and D1 activity were reduced in the liver and the kidney of IE-treated animals. Finally, the mRNA expression of Slc5a5 and Slc26a4 were reduced in the mammary gland of IE-exposed rats. The latter results are in accordance with the reduction of prolactin expression and serum levels in IE-treated dams. In summary, our study indicates that the exposure to IE during pregnancy and lactation induces primary hypothyroidism in rat dams and impairs iodide transfer to the milk.

A PRISMA-compliant systematic review and meta-analysis of the relationship between thyroid disease and different levels of iodine intake in mainland China

BACKGROUND

Low-iodine intake has historically been an issue in China, causing widespread iodine deficiency diseases (IDD). China started to introduce universal salt iodization in 1995, but reports of increased thyroid disease are a concern and appropriate levels of iodine intake must be considered.

OBJECTIVE

To assess the prevalence of thyroid disease with different urinary iodine concentrations (UICs) in the general population of those residing in mainland China. Furthermore, we aimed to analyze the relationship between thyroid disease and UIC, to provide guidance in establishing effective health policies regarding iodine intake.

METHODS

PubMed, Cochrane, Embase, CNKI, Wan fang, and CQVIP databases were searched for random community-based relevant studies with UIC published before January 2016 in mainland China. Two independent reviewers extracted data from eligible citations, and obtained prevalence of thyroid disease for different UICs, as well as the intergroup interaction P values.

RESULTS

Forty-three articles were included. The prevalence of thyroid nodules was 22.3% (95% confidence interval [CI]: 20.6%-24.1%) for the low-iodine group, 25.4% (95% CI: 20.8%-28.8%) for the medium-iodine group, and 6.8% (95% CI: 2.8%-11.5%) for the high-iodine group. In the high-iodine group, the prevalence of thyroid nodules was lower than the other groups. The prevalence of 8.3% (95% CI: 3.8%-17.3%) for subclinical hypothyroidism in the high-iodine group was significantly higher than the low- and medium-iodine groups (P < .01). The prevalence of hypothyroidism in the medium-iodine group was 0.2% (95% CI: 0.1%-0.4%), and was lower than the prevalence of the other 2 groups (P < .01). There was no difference in prevalence of hyperthyroidism in each group.

CONCLUSIONS

Thyroid nodules are the most easily detectable thyroid disease. These have a lower prevalence in the high-iodine group. The prevalence of most thyroid diseases is lowest for a UIC ranging from 100 to 299 μg/L. This serves as a reference for health policy-making with respect to iodine levels. Further studies on this topic should be carried out according to sufficient thyroid cancer data.

Population-Based National Prevalence of Thyroid Dysfunction in Spain and Associated Factors: Di@bet.es Study

BACKGROUND

The aim of this study was to investigate the national prevalence of thyroid dysfunction in Spain and its association with various clinical, environmental, and demographic variables.

METHODS

The study included 4554 subjects (42.4% men) with a mean age of 50 years (range 18-93 years), who were participants in a national, cross-sectional, population-based survey conducted in 2009-2010. Data gathered included clinical and demographic characteristics, physical examination, and blood sampling. Thyrotropin, free thyroxine, free triiodothyronine, and thyroid peroxidase antibody (TPOAb) concentrations were analyzed by electrochemiluminescence. Urinary iodine (UI) levels were measured in an isolated urine sample.

RESULTS

The prevalence of treated hypothyroidism, untreated subclinical hypothyroidism, and untreated clinical hypothyroidism was 4.2% [confidence interval (CI) 3.6-4.9%], 4.6% [CI 4.0-5.2%], and 0.3% [CI 0.1-0.5%], respectively. The prevalence of total hypothyroidism (including all fractions) was 9.1% [CI 8.2-10.0%]. The prevalence of total hyperthyroidism was 0.8% [CI 0.6-1.1]. A total of 7.5% [CI 6.7-8.3%] of the population tested positive for TPOAbs (≥50 IU/mL). In multivariate logistic regression models, TPOAbs were strongly associated with both hypothyroidism (p < 0.001) and hyperthyroidism (p = 0.005), whereas high UI levels (>200 μg/g creatinine) were associated with hypothyroidism (p < 0.001). The positive association between UI and hypothyroidism remained for both treated (p < 0.001) and untreated (p < 0.05) hypothyroidism, whereas it was especially significant for non-autoimmune (TPOAbs negative) forms (p < 0.001). At UI levels ≥200 μg/g, there was a positive correlation between UI and thyrotropin levels (β = 0.152, p < 0.001) and a negative correlation between UI and free triiodothyronine levels (β = -0.134, p = 0.001).

CONCLUSION

According to the data, a large proportion (10%) of the Spanish population has some evidence of thyroid dysfunction. High TPOAb concentrations were associated with both hypo- and hyperthyroidism, whereas high UI concentrations were associated with hypothyroidism.

Effect of Prolonged Iodine Overdose on Type 2 Iodothyronine Deiodinase Ubiquitination-Related Enzymes in the Rat Pituitary

The purpose of this study is to determine the effect of prolonged iodine overdose on type 2 iodothyronine deiodinase (D2) ubiquitination-related enzymes. Male Wistar rats were fed different doses of iodine and were then euthanized at the 4, 8, 12, or 24 weeks (4w, 8w, 12w, or 24w) after iodine administration. Urinary iodine concentration (UIC), thyroid-stimulating hormone (TSH), total thyroxine (TT4), and total triiodothyronine (TT3) were determined. Real-time quantitative RT-PCR and Western blot were used to measure mRNA and protein expression levels of pituitary D2 as well as two D2-specific ubiquitin ligases [WD repeat and SOCS box-containing protein 1 (WSB-1), membrane-associated ring finger (C3HC4) 6 (MARCH6 or TEB4)] and two D2-specific deubiquitinating enzymes [ubiquitin-specific peptidase 20 (USP20) and ubiquitin-specific peptidase 33 (USP33)]. The mRNA and protein expression levels of USP19, a TEB4-specific deubiquitinating enzyme, were also measured. Prolonged high iodine intake significantly increased TSH expression. At 12w, TSH was 1.57-, 1.44-, and 2.11-fold of NI group in 6HI, 10HI, and 50HI groups, respectively. At 24w, TSH had increased to 2.11-fold in the 50HI group. The pituitary D2 protein level decreased at 12w and 24w; though the mRNA level did not change. Prolonged iodine intake increased mRNA and protein expression levels of pituitary WSB-1 and TEB4. High iodine intake had no discernible effects on USP20. Temporary increases in USP33 and USP19 mRNA levels were observed. The enzymes related to D2 ubiquitination change with prolonged high iodine intake. Increased D2 ubiquitination suppresses the activity of D2, causing a decrease in negative feedback of the hypothalamic-pituitary-thyroid axis.

Underlying Mechanisms of Pituitary-Thyroid Axis Function Disruption by Chronic Iodine Excess in Rats

BACKGROUND

Iodine is essential for thyroid hormone synthesis and is an important regulator of thyroid function. Chronic iodine deficiency leads to hypothyroidism, but iodine excess also impairs thyroid function causing hyperthyroidism, hypothyroidism, and/or thyroiditis. This study aimed to investigate the underlying mechanisms by which exposure to chronic iodine excess impairs pituitary-thyroid axis function.

METHODS

Male Wistar rats were treated for two months with NaI (0.05% and 0.005%) or NaI+NaClO₄ (0.05%) dissolved in drinking water. Hormone levels, gene expression, and thyroid morphology were analyzed later.

RESULTS

NaI-treated rats presented high levels of iodine in urine, increased serum thyrotropin levels, slightly decreased serum thyroxine/triiodothyronine levels, and a decreased expression of the sodium-iodide symporter, thyrotropin receptor, and thyroperoxidase mRNA and protein, suggesting a primary thyroid dysfunction. In contrast, thyroglobulin and pendrin mRNA and protein content were increased. Kidney and liver deiodinase type 1 mRNA expression was decreased in iodine-treated rats. Morphological studies showed larger thyroid follicles with higher amounts of colloid and increased amounts of connective tissue in the thyroid of iodine-treated animals. All these effects were prevented when perchlorate treatment was combined with iodine excess.

CONCLUSIONS

The present data reinforce and add novel findings about the disruption of thyroid gland function and the compensatory action of increased thyrotropin levels in iodine-exposed animals. Moreover, they draw attention to the fact that iodine intake should be carefully monitored, since both deficient and excessive ingestion of this trace element may induce pituitary-thyroid axis dysfunction.

Iodine Status and Prevalence of Thyroid Disorders After Introduction of Mandatory Universal Salt Iodization for 16 Years in China: A Cross-Sectional Study in 10 Cities

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.

Iodine nutrition and thyroid diseases in Chengdu, China: an epidemiological study

OBJECTIVE

To assess the iodine nutritional status and investigate the prevalence of thyroid diseases in a community population in Chengdu, China.

METHODS

Eighty school-age children were randomly selected for measurements of urinary iodine concentration. A total of 1500 residents over the age of 18 who had lived in Chengdu for more than 5 years were selected by stratified cluster sampling. Serum thyroid hormone concentrations and thyroid autoantibodies were measured, and thyroid ultrasonography was performed.

RESULTS

The median urine iodine concentration was 184 µg/l in school-age children. The prevalence of clinical hyperthyroidism, subclinical hyperthyroidism, clinical hypothyroidism and subclinical hypothyroidism was 0.97%, 1.95%, 0.90% and 5.55%, respectively. The prevalence of thyroid autoantibodies and thyroid nodules was 15.82% and 16.87%, respectively. The prevalence of clinical hyper- and hypothyroidism was greater in females than in males (P < 0.05). The prevalence of subclinical hyper- and hypothyroidism, thyroid nodules and thyroid autoantibodies increased significantly with age (P < 0.05). The rate of new abnormal TSH was 9.37%, and the average serum Thyroid Stimulating Hormone (TSH) concentrations increased with age. When TSH >0.71 mU/l, the prevalence of positive TPOAb and/or TgAb increased significantly with rising concentrations of TSH (P < 0.05); however, the prevalence of thyroid nodules did not increase with escalating concentrations of TSH (P = 0.09).

CONCLUSION

Subclinical thyroid diseases, especially subclinical hypothyroidism and thyroid nodules, are common in an iodine sufficient area. Females and the elderly might benefit from routine screening for thyroid diseases, followed by appropriate detection and treatment.

Iodine deficiency and thyroid disorders

Iodine deficiency early in life impairs cognition and growth, but iodine status is also a key determinant of thyroid disorders in adults. Severe iodine deficiency causes goitre and hypothyroidism because, despite an increase in thyroid activity to maximise iodine uptake and recycling in this setting, iodine concentrations are still too low to enable production of thyroid hormone. In mild-to-moderate iodine deficiency, increased thyroid activity can compensate for low iodine intake and maintain euthyroidism in most individuals, but at a price: chronic thyroid stimulation results in an increase in the prevalence of toxic nodular goitre and hyperthyroidism in populations. This high prevalence of nodular autonomy usually results in a further increase in the prevalence of hyperthyroidism if iodine intake is subsequently increased by salt iodisation. However, this increase is transient because iodine sufficiency normalises thyroid activity which, in the long term, reduces nodular autonomy. Increased iodine intake in an iodine-deficient population is associated with a small increase in the prevalence of subclinical hypothyroidism and thyroid autoimmunity; whether these increases are also transient is unclear. Variations in population iodine intake do not affect risk for Graves' disease or thyroid cancer, but correction of iodine deficiency might shift thyroid cancer subtypes toward less malignant forms. Thus, optimisation of population iodine intake is an important component of preventive health care to reduce the prevalence of thyroid disorders.

Effects of increased iodine intake on thyroid disorders

Iodine is a micronutrient essential for the production of thyroid hormones. Iodine deficiency is the most common cause of preventable mental impairment worldwide. Universal salt iodization (USI) has been introduced in many countries as a cost-effective and sustainable way to eliminate iodine deficiency disorders for more than 25 years. Currently, the relationship between USI and iodine excess has attracted more attention. Iodine excess can lead to hypothyroidism and autoimmune thyroiditis, especially for susceptible populations with recurring thyroid disease, the elderly, fetuses, and neonates. Nationwide USI was introduced in China in 1996. This review focused on the effects of iodine excess worldwide and particularly in China.

Dietary iodine and selenium affected the mRNA expression levels of skin monodeiodinase (II, III) in Liaoning Cashmere goats

Livestock are frequently provided nutrient-depleted diets, which can negatively impact animal health and productivity. In our previous trial, we found that iodine (I) supplementation (not selenium (Se)) could increase cashmere production. In order to explore the role of I and Se in cashmere growth, we investigated the effects of dietary I and Se supplementation in Liaoning cashmere goats. Serum thyroid hormone status and the mRNA expression levels of skin monodeiodinase (MDII, MDIII) were measured during the cashmere fiber growth period. Forty-eight 2.5-year-old Liaoning cashmere goats (38.6 ± 2.65 kg BW) were divided into six equal groups, and their diets were supplemented with I (0, 2, or 4 mg/kg DM) and Se (0 or 1 mg/kg DM) in a 2 × 3 factorial treatment design. The six treatment groups were: I(0)Se(0), I(2)Se(0), I(4)Se(0), I(0)Se(1), I(2)Se(1), and I(4)Se(1). Concentrations of I and Se in the basal diet (group I(0)Se(0)) were 0.67 and 0.09 mg/kg DM, respectively. The trial started in September of 2009 and lasted 70 days. For every measured parameter, supplemental Se had no significant effect on thyroid hormones, but improved the mRNA expression levels of skin MDIII (P < 0.01). However, supplemental I increased levels of thyroid hormones (thyroxine and triiodothyronine) and improved the mRNA expression levels of skin MDII (P < 0.05). These results show that the addition of I to cashmere goat feedstock may be an effective means of increasing cashmere production through thyroid hormones regulating the mRNA expression of skin MDII.