Relationship between excess iodine, thyroid function, blood pressure, and blood glucose level in adults, pregnant women, and lactating women: A cross-sectional study

Long-term iodine deficiency and excess inhibit β-casein and α-lactalbumin secretion of milk in lactating rats

Iodine is critical for thyroid hormone synthesis and developmental programming in the first 1,000 days of life. The effect of maternal iodine on milk protein secretion remains unknown. We aimed to explore the effect of long-term maternal iodine deficiency and excess on milk protein secretion in lactating rats and its mechanisms preliminarily. Animal models of iodine deficiency and excess were generated by treating Wistar rats a low-iodine diet and deionized water with different potassium iodide concentrations from reproductive age to lactation. Under iodine deficiency, CSN2 and α-LA secretion of milk was inhibited in early and mid-lactation, respectively, and the inhibition of milk CSN2 and α-LA secretion weakened in late lactation. Under iodine excess, milk CSN2 secretion was inhibited in early lactation, and the inhibition of milk CSN2 and α-LA secretion was more pronounced in late lactation. Under iodine deficiency and excess, the concentrations of CSN2 and α-LA and protein expression levels of THRα1, THRβ1, and PRLR in the mammary gland decreased. These results demonstrate the negative impact of long-term maternal iodine malnutrition on milk protein secretion.

Study on the Applicability of WHO Serum Iodine Standards for Normal Individuals in the Chinese Population-A Cross-sectional Study from Six Provinces in China

This study aims to assess the applicability of the serum iodine (SI) standards proposed by the WHO and other renowned laboratories for the Chinese population. Additionally, it seeks to establish reference intervals (RIs) for SI in Chinese adults and conduct a risk assessment between serum iodine concentration (SIC) and the development of thyroid diseases. This study enrolled 3138 adults aged 18-60 years from six provinces in China. A total of 1794 healthy adults with normal thyroid function were selected to assess the applicability of the international standards and establish China's RI, utilizing five external datasets for validation. Multiple logistic regression analysis was applied to explore the relationship between SIC and thyroid disease. The ratios of adults with normal thyroid function from five provinces whose SI levels fall outside the limits of the international standards are partially greater than 10%. China's RI was 40.11-97.59 µg/L, and the ratios of individuals in the validation datasets outside this RI were all less than 10%. Adults with low SIC levels (< 40.11 µg/L) were at higher risk of hypothyroxinemia (adjusted OR = 4.715, 95% CI = 1.459-15.235), overt hypothyroidism (adjusted OR = 4.719, 95% CI = 1.583-14.067), and autoimmune thyroiditis (adjusted OR = 2.394, 95% CI = 1.410-4.064). Adults with high SIC levels (> 97.59 µg/L) were at a higher risk of overt hyperthyroidism (adjusted OR = 18.170, 95% CI = 5.940-55.577). These international standards are not fully applicable to the Chinese population. We established RIs for SI in Chinese adults to better accommodate the country's specific conditions.

Effect of decitabine on PD-L2 methylation in whole blood of iodine-induced autoimmune thyroiditis rats

Excessive iodine intake can induce autoimmune thyroiditis (AIT), and the methylation of programmed death receptor 2 (PD-L2) may be involved in the development of iodine-induced AIT. Here, we investigated the immune role of methylation of the susceptibility gene PD-L2 in the occurrence of iodine-induced AIT using the DNA methyltransferase inhibitor Decitabine (Dec) in an experimental autoimmune thyroiditis (EAT) rat model. After injecting Dec intraperitoneally into EAT rats, we performed arsenic-cerium catalytic spectrophotometry, pathological hematoxylin and eosin staining, enzyme-linked immunosorbent assay, quantitative methylation-specific polymerase chain reaction (qMSP), and quantitative real-time polymerase chain reaction (qPCR) to determine the relevant indices. The results showed that compared with the control group, the urinary iodine, thyroid lymphocyte infiltration, thyroglobulin antibody (TgAb), interferon (IFN-γ), and interleukin (IL-23) levels of the EAT rats were significantly increased. The PD-L2 methylation levels were significantly decreased in EAT rats compared to control rats, and the mRNA expression of the PD-L2 was significantly increased. Following Dec intervention, the methylation level of the PD-L2 in rats increased and interferon and interleukin-23 levels decreased, albeit not significantly. However, the mRNA expression of PD-L2 decreased significantly after Dec intervention, and the thyroid function of EAT rats also showed a gradual improvement trend. In summary, hypomethylation of PD-L2 is closely related to the development of iodine-induced AIT. Pro-inflammatory cellular factors are also involved in iodine-induced AIT progression. Although Dec shows promise in the treatment of AIT, further evaluation of its safety is necessary.

High Water Iodine Concentrations Are Associated With the Prevalence of Subclinical Hypothyroidism, Thyroid Nodules, and Goiter Among Pregnant Women in Shandong, China

BACKGROUND

Both iodine deficiency and iodine excess can harm the thyroid glands during pregnancy. In areas without iodine fortification, the relationship between the water iodine concentration (WIC) and thyroid disease in pregnant women requires further investigation.

OBJECTIVES

The aim of this study was to evaluate the relationship between WICs and the prevalence of thyroid disease in pregnant women residing in areas with high WICs without access to iodized salt.

METHODS

A cross-sectional survey was conducted in Shandong Province. Water and urine samples were collected, and the iodine content was assessed. Venous blood samples were taken to measure thyroid hormones and antibodies. Ultrasound was used to assess thyroid size and detect nodules.

RESULTS

A total of 1073 pregnant women were included in this study. As the WIC increased, the urinary iodine concentration also increased, according to linear regression analysis (β: 0.5; P < 0.001). The lowest prevalence of subclinical hypothyroidism (SH) and thyroid dysfunction (TD) was observed at a WIC of 10-40 μg/L, whereas the lowest prevalence of thyroid nodules (TNs) and goiter was seen at a WIC of 40-100 μg/L. Logistic regression analysis showed that WIC was significantly associated with thyroid diseases. WIC of <10 μg/L was associated with TD prevalence (OR: 1.8; 95% CI: 1.1, 3.1), and WIC of >100 μg/L was associated with SH, TN, and goiter prevalence (SH-OR: 10.8; 95% CI: 1.4, 84.0; TN-OR: 2.5; 95% CI: 1.1, 5.6; goiter-OR: 2.4; 95% CI: 1.1, 5.6).

CONCLUSIONS

WIC is associated with thyroid function among pregnant women. WIC of <10 μg/L is a risk factor for TD, whereas WIC of >100 μg/L is a risk factor for SH, TN, and goiter. These findings suggest that intermediate WICs are most conducive to thyroid health in pregnant women and that assessing local WICs could help improve maternal health.

Genome-wide association studies of thyroid-related hormones, dysfunction, and autoimmunity among 85,421 Chinese pregnancies

Maintaining normal thyroid function is crucial in pregnancy, yet thyroid dysfunction and the presence of thyroid peroxidase antibodies (TPOAb) affect 0.5% to 18% of pregnant women. Here, we conducted a genome-wide association study (GWAS) of eight thyroid traits, including two thyroid-related hormones, four thyroid dysfunctions, and two thyroid autoimmunity measurements among 85,421 Chinese pregnant women to investigate the genetic basis of thyroid function during pregnancy. Our study identified 176 genetic loci, including 125 previously unknown genome-wide associations. Joint epidemiological and Mendelian randomization analyses revealed significant associations between the gestational thyroid phenotypes and gestational complications, birth outcomes, and later-age health outcomes. Specifically, genetically elevated thyroid-stimulating hormone (TSH) levels during pregnancy correlated with lower glycemic levels, reduced blood pressure, and longer gestational duration. Additionally, TPOAb and thyroid functions during pregnancy share genetic correlations with later-age thyroid and cardiac disorders. These findings provide insights into the genetic determinants of thyroid traits during pregnancy, which may lead to new therapeutics, early pre-diagnosis and preventive strategies starting from early adulthood.

Excess Iodine Consumption Induces Oxidative Stress and Pancreatic Damage Independently of Chemical Form in Male Wistar Rats: Participation of PPAR-γ and C/EBP-β

BACKGROUND

Human beings consume different chemical forms of iodine in their diet. These are transported by different mechanisms in the cell. The forms of iodine can be part of thyroid hormones, bind to lipids, be an antioxidant, or be an oxidant, depending on their chemical form. The excessive consumption of iodine has been associated with pancreatic damage and diabetes mellitus type 2, but the association between disease and the chemical form consumed in the diet is unknown. This research analyzes the effect of excessive iodine consumption as Lugol (molecular iodine/potassium iodide solution) and iodate on parameters of pancreatic function, thyroid and lipid profiles, antioxidant and oxidant status, the expression of IR/Akt/P-Akt/GLUT4, and transcription factors PPAR-γ and CEBP-β.

METHODS

Three groups of Wistar rats were treated with 300 μg/L of iodine in drinking water: (1) control, (2) KIO3, and (3) Lugol.

RESULTS

Lugol and KIO3 consumption increased total iodine levels. Only KIO3 increased TSH levels. Both induced high serum glucose levels and increased oxidative stress and pancreatic alpha-amylase activity. Insulin levels and antioxidant status decreased significantly. PPAR-γ and C/EBP-β mRNA expression increased.

CONCLUSION

The pancreatic damage, hypertriglyceridemia, and oxidative stress were independent of the chemical form of iodine consumed. These effects depended on PPAR-γ, C/EBP-β, GLUT-4, and IR.

Association between physical activity and thyroid function in American adults: a survey from the NHANES database

OBJECTIVE

Physical activity (PA) is closely related to our lives, and the effects of PA on thyroid function have not been elucidated.

METHODS

Using data from the National Health and Nutrition Examination Survey (NHANES) 2007-2012, we included 5877 participants and analyzed the associations of thyroid function with weekly physical activity (PAM, expressed in metabolic equivalents of task) and physical activity time (PAT) in American adults. Univariate and multivariate logistic analyses were used to demonstrate the associations of PAM and PAT with the primary outcome. Linear regression analysis was performed to determine the associations between thyroid biochemical indicators/diseases and PAM/PAT.

RESULTS

Our study revealed noticeable sex differences in daily PA among the participants. The odds ratio of the fourth versus the first quartile of PAM was 3.07 (confidence interval, CI [1.24, 7.58], p = 0.02) for overt hypothyroidism, 3.25 (CI [1.12, 9.45], p = 0.03) for subclinical hyperthyroidism in adult men. PAT in the range of 633-1520 min/week was found to be associated with the occurrence of subclinical hyperthyroidism [p < 0.001, OR (95% CI) = 5.89 (1.85, 18.80)], PAT of the range of > 1520 min/week was found to be associated with the occurrence of overt hypothyroidism [p < 0.001, OR (95% CI) = 8.70 (2.80, 27.07)] and autoimmune thyroiditis (AIT) [p = 0.03, OR (95% CI) = 1.42 (1.03, 1.97)] in adult men. When PAM < 5000 MET*minutes/week or PAT < 1000 min/week, RCS showed an L-shaped curve for TSH and an inverted U-shaped curve for FT4. The changes in FT3 and TT3 in men were linearly positively correlated with PAM and PAT, while TT4 is linearly negatively correlated.

CONCLUSION

The amount of daily physical activity of American adults is strongly associated with changes in thyroid function, including thyroid hormone levels and thyroid diseases. Thyroid hormone levels were varied to a certain extent with changes in PAM and PAT.

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.

Association of serum thyroid hormone and coronary artery calcification in patients who underwent invasive coronary angiography: an observational study

BACKGROUND

Thyroid hormones (TH) are known to have a range of effects on the cardiovascular system. However, there is still controversy regarding the relationship between thyroid function and coronary artery calcification (CAC). The purpose of this paper is to investigate the relationship between TH and CAC, especially severe CAC, in patients who underwent invasive coronary angiography (ICA). This may provide further insights into the potential role of TH in the development and progression of cardiovascular disease.

METHOD

This observational study included 4221 patients who underwent ICA after completing CTA in a single center. We collected demographic, clinical, and laboratory data from electronic medical records and measured CAC scores via non-contrast cardiac CT.

RESULT

The study found that there is a negative correlation between the CAC score and FT3 level, even after adjusting for potential confounding factors, but there was no correlation between the CAC score and FT4 or TSH. When categorized into quartiles, the highest quartile of FT3 was associated with a decrease (β = -104.37, 95%CI: -172.54, -36.21) in calcification score compared to the lowest quartile. This correlation was more significant in the subgroup of individuals with diabetes or hypertension.

CONCLUSION

The study found a negative correlation between FT3 and CAC in patients who underwent ICA. The correlation was consistent with other studies and may suggest that low levels of FT3 are associated with severe CAC. The study may provide new evidence for future research on CAC and potential therapeutic approaches.

Dietary protein intake affects the association between urinary iodine and clinically relevant depression: Evidence from NHANES 2007-2018

Both iodine concentration and protein intake are important nutritional factors that may influence the development of depressive symptoms. However, there are no studies on the effect of protein intake on the relationship between iodine concentration and the risk of depression. The study aimed to explore the relationship between iodine and the risk of clinically relevant depression (CRD) according to protein intake. This study analyzed the adults (≥18 years) who participated in the 2007-2018 National Health and Nutrition Cross-sectional Survey (N = 10,462). CRD was assessed using the Patient Health Questionnaire (PHQ-9). Protein intake was assessed using two 24-h dietary recalls and urinary iodine concentration (UIC) was measured using inductively coupled plasma dynamic response cell mass spectrometry. Weighted multivariate logistic regression and restrictive cubic splines were performed to assess the relationship between UIC and CRD according to protein category (low protein intake <0.8 g/kg/day; high protein intake: ≥0.8 g/kg/day). After controlling for sociodemographic, behavioral, chronic diseases, and dietary factors, a positive correlation was observed between UIC (log10) and CRD (OR: 1.36, 95% CI: 1.026, 1.795). Low UIC (<100 μg/L) was associated with a lower prevalence of CRD (OR: 0.73, 95% CI: 0.533, 0.995) in high protein intake individuals, whereas this relationship did not exist in those with low protein intake. Moreover, restrictive cubic splines confirmed a near L-shaped relationship between UIC and CRD in the low-protein group (nonlinear p = .042) and a linear relationship between them in the high-protein group (nonlinear p = .392). This study illustrates that protein intake affects the relationship between UIC and CRD. Combining lower UIC and high protein intake may help reduce the prevalence of CRD, which would have significant implications for managing patients with depressive CRD in the clinical setting.

Effect of different iodide intake during pregnancy and lactation on thyroid and cardiovascular function in maternal and offspring rats

OBJECTIVE

We aimed to investigate the impact of different iodide intake during pregnancy and lactation on iodine concentration in urine and serum, fatty acid metabolism, thyroid and cardiovascular function in maternal and offspring rats.

METHODS

Pregnant rats were randomly assigned to four groups: normal adult iodide intake (NAI, 7.5 μg/d), normal pregnant iodide intake (NPI, 12.5 μg/d), 5 times (5 HI, 62.5 μg/d) and 10 times higher-than-normal pregnant iodide intake (10 HI, 125 μg/d). The maternal rats were continuously administered potassium iodide until postnatal day 16 (PN16). Thyroid function was measured by enzyme-linked immunosorbent assay (ELISA). The iodine concentration in urine and serum were detected by inductively coupled plasma mass spectrometry (ICP-MS). The messenger ribonucleic acid (mRNA) expressions of Krüppel-like factor 9 (KLF9) and thioredoxin reductase 2 (Txnrd2) were measured using quantitative real-time polymerase chain reaction (RT-qPCR). Characteristic distribution of KLF9 expression and its interaction with TRβ was assessed by immunohistochemical and immunofluorescence staining. Serum fatty acids were analyzed by Liquid Chromatography-Mass Spectrometry (LC-MS). Cardiac function and blood pressure were measured by echocardiography and a non-invasive tail-cuff system.

RESULTS

High iodide intake (5 HI and 10 HI) during pregnancy and lactation results in increased urinary iodine concentration (UIC), serum total iodine concentration (STIC) and serum non-protein-bound iodine concentration (SNBIC) in both maternal and offspring rats, along with significantly increased FT3 and its target gene expression of KLF9. In maternal rats of both 5 HI and 10 HI groups, systolic blood pressure (SBP) was significantly higher, the increased SBP was significantly correlated with the increased UIC (r = 0.968, p = 0.002; r = 0.844, p = 0.035), KLF9 (r = 0.935, p = 0.006; r = 0.954, p = 0.003) and the decreased Txnrd2 (r = -0.909, p = 0.012; r = -0.912, p = 0.011). In maternal rats of 10 HI group, cardiac hyperfunction with increased LVEF, LVFS and decreased LVESD were observed. The increased LVEF and decreased LVESD were significantly correlated with UIC, STIC and SNBIC (r = 0.976, p = 0.001; r = 0.945, p = 0.005; r = 0.953, p = 0.003; r = -0.917, p = 0.01; r = -0.859, p = 0.028; r = -0.847, p = 0.033), LVEF, LVFS and LVESD were significant correlated with KLF9 (r = 0.950, p = 0.004; r = 0.963, p = 0.002; r = -0.990, p = 0.0002) and Txnrd2 expression (r = -0.979, p = 0.001; r = -0.915, p = 0.01; r = 0.933, p = 0.007), and the decreased LVESD was correlated with decreased epoxyeicosatrienoic acid (EET) metabolites: 5,6-EET, 8,9-DHET and 11,12-DHET (r = 0.999, p = 0.034; r = 1.000, p = 0.017; r = 1.000, p = 0.017). While in offspring rats, no significant change in SBP and cardiac function was found. STIC and SNBIC were much lower than those in maternal rats, and eicosapentaenoic acid (EPA) metabolites (9-HEPE, 15-HEPE and 14,15 DiHETE) were significantly increased.

CONCLUSION

In addition to thyroid hormones, STIC, SNBIC, KLF9, Txnrd2, EET and EPA metabolites might be promising biomarkers in high iodide intake-induced thyroid and cardiovascular function.

Prevalence of Excessive Iodine Intake in Pregnancy and Its Health Consequences: Systematic Review and Meta-analysis

The objective was to estimate the prevalence of excessive iodine intake in pregnant women and to investigate the consequences for maternal-fetal health. The systematic review was based on PRISMA. The search was conducted in September 2021 in LILACS, PubMed/MEDLINE, Science Direct, and SCOPUS databases. Observational studies that assessed excessive nutritional iodine status in pregnancy diagnosed by urinary iodine concentration and associated it with biomarkers of thyroid health function were included. Study selection, data extraction, and risk of biased evaluation were performed independently. Meta-analysis was calculated using a fixed and random effect model, and heterogeneity was assessed by the chi-square test. Meta-regressions were performed to identify the causes of heterogeneity using the Knapp and Hartung test. Nine studies were included in the systematic review, and eight in the meta-analysis. The prevalence of excessive iodine intake in 10,736 pregnant women in different regions of the world was 52%. The main implications for pregnant women were hypothyroxinemia, hypothyroidism, and hyperthyroidism. For the newborn, macrosomia and thyroid dysfunction. In addition, drinking water with high iodine intake contributed to excessive iodine intake. Therefore, the prevalence of iodine excess was 52%, with high heterogeneity among studies, explained by trimester of gestation and FT4 level; therefore, the farther the trimester of gestation and the lower the FT4, the higher the prevalence of iodine excess. PROSPERO Registration: CRD420206467 ( https://www.crd.york.ac.uk/prospero/display_record.php?RecordID=206467 ).

Serum thyroglobulin as a biomarker of iodine excess and thyroid disease occurrence in adults

BACKGROUND

Thyroglobulin (Tg) is considered a sensitive indicator of iodine deficiency. However, the usefulness of Tg as a biomarker of excess iodine is uncertain. The present study aimed to determine the influence of different iodine intake on serum Tg levels, evaluate the influence of thyroid diseases on the distribution of Tg, and identify the factors that may affect Tg levels.

METHODS

A cross-sectional survey with a total of 1208 adults was conducted in different water iodine areas in China. Urinary iodine concentration (UIC), water iodine concentration (WIC), serum Tg, thyroid-stimulating hormone (TSH), and thyroid antibodies were measured. The thyroid volumes and nodules were measured by B-scan ultrasound.

RESULTS

Based on the WIC data, subjects were divided into three groups. Based on the median urinary iodine concentration (MUIC) data, the iodine levels were adequate, more than adequate, and excess for the WIC < 10 μg/L group, 10 μg/L ≤ WIC ≤ 100 μg/L g, and WIC > 100 μg/L groups, respectively. The median Tg was significantly higher in the excess iodine group than in the adequate iodine group and the more than adequate iodine group (14.6 μg/L vs.12.7 μg/L, P = 0.042; 14.6 μg/L vs.12.5 μg/L, P = 0.004). Multiple linear regression analysis showed that excess iodine intake, goitre, thyroid nodules, and hypothyroidism were significantly related to higher serum Tg levels.

CONCLUSION

Serum Tg level can be a promising biomarker of excessive iodine intake, but other factors, especially the presence of thyroid disease, should be considered when using this parameter.

Does Iodine Influence the Metabolism of Glucose?

Thyroid function and glucose status are linked; experimental, clinical, and epidemiological studies have shown this. Iodine is a vital trace element that is inextricably linked to thyroid hormone synthesis. The latter is also associated with glucose metabolism and diabetes. Recently, some-but not all-studies have shown that iodine is linked to glucose metabolism, glucose intolerance, impaired fasting glucose, prediabetes, diabetes mellitus, or gestational diabetes. In this concise review, we review these studies, focusing on iodine and glucose metabolism and prediabetic conditions or type 2 diabetes mellitus. The potential beneficial effect of iodine on glucose metabolism may be attributed to its antioxidant properties.

Relationship between water iodine and children's goiters

Excessive iodine can lead to goiters. However, the relationship between the water iodine concentration (WIC) and goiter rate (GR) is unclear. This study aims to explore the factors that influence children's GR in areas with high WIC and analyse the threshold value of the GR increase associated with the WIC. According to the monitoring of the areas with high WIC in China in 2018-2020, a total of 54 050 children in eight high water iodine provinces were chosen. Drinking water, urine and edible salt samples of children were collected. The thyroid volume (Tvol) was measured. A generalised additive model (GAM) was used to analyse the relationship between the WIC and GR in children. Among the 54 050 children in areas with high WIC, the overall GR was 3·34 %, the median of water iodine concentration was 127·0 µg/l, the median of urinary iodine concentration was 318 µg/l and the non-iodised salt coverage rate (NISCR) was 63·51 %. According to the GAM analysis results, water iodine and urinary iodine are factors that influence the Tvol and GR, while the NISCR affects only the GR. When the WIC was more than 420 µg/l or the urinary iodine concentration was more than 800 µg/l, the GR increased rapidly. When the NISCR reached more than 85 %, the GR was the lowest. Thus, in areas with high WIC, WIC more than 420 µg/l may increase the risk of goiter, and the NISCR should be increased to over 85 % to avoid goiters in children.

Iodine as a potential endocrine disruptor-a role of oxidative stress

PURPOSE

Iodine is an essential micronutrient required for thyroid hormone biosynthesis. However, overtreatment with iodine can unfavorably affect thyroid physiology. The aim of this review is to present the evidence that iodine-when in excess-can interfere with thyroid hormone synthesis and, therefore, can act as a potential endocrine-disrupting chemical (EDC), and that this action, as well as other abnormalities in the thyroid, occurs-at least partially-via oxidative stress.

METHODS

We reviewed published studies on iodine as a potential EDC, with particular emphasis on the phenomenon of oxidative stress.

RESULTS

This paper summarizes current knowledge on iodine excess in the context of its properties as an EDC and its effects on oxidative processes.

CONCLUSION

Iodine does fulfill the criteria of an EDC because it is an exogenous chemical that interferes-when in excess-with thyroid hormone synthesis. However, this statement cannot change general rules regarding iodine supply, which means that iodine deficiency should be still eliminated worldwide and, at the same time, iodine excess should be avoided. Universal awareness that iodine is a potential EDC would make consumers more careful regarding their diet and what they supplement in tablets, and-what is of great importance-it would make caregivers choose iodine-containing medications (or other chemicals) more prudently. It should be stressed that compared to iodine deficiency, iodine in excess (acting either as a potential EDC or via other mechanisms) is much less harmful in such a sense that it affects only a small percentage of sensitive individuals, whereas the former affects whole populations; therefore, it causes endemic consequences.

Relationships between the serum TPOAb and TGAb antibody distributions and water iodine concentrations, thyroid hormones and thyroid diseases: a cross-sectional study of 2503 adults in China

The aim of this study was to explore the status of thyroid peroxidase antibody (TPOAb) and thyroglobulin antibody (TGAb) in three areas with differing water iodine concentrations; and to discuss the relationships between these two thyroid antibodies and thyroid diseases in the three areas. We investigated 2503 adults from three areas. Urinary iodine concentrations, thyroid stimulating hormone (TSH), free thyroxine (FT4), free triiodothyronine (FT3), TPOAb, TGAb and thyroid volume (TV) were measured, and thyroid ultrasonography was performed. The positivity rates of TGAb(+), TPOAb(+) and TGAb(+) and TPOAb(+) or TGAb(+) were significantly higher in iodine fortification (IF) areas than iodine adequate (IA) areas (all P < 0·05). In IF and iodine excess areas, the positivity rates of TPOAb(+), TGAb(+) and TPOAb(+) or TGAb(+) significantly increased with age (all P for trend < 0·05). The levels of TSH, TV and the prevalence of overt hypothyroidism, subclinical hypothyroidism and goitre were significantly elevated in the thyroid antibody-positive groups in the three areas, but the FT3 was diminished (all P < 0·010). Positivity for TPOAb and TGAb was associated with an increased risk of subclinical hypothyroidism in the three areas. In areas with different median water iodine, positivity for both TPOAb and TGAb was associated with elevated TSH values. Notably, with the increased levels of TPOAb, the frequency of abnormally elevated TSH increased dramatically in the three areas.

The Effects of Long-Term High Water Iodine Levels in the External Environment on the Carotid Artery

Iodine excess typically affects thyroid function in the human body and may damage carotid artery. Four investigation plots with different water iodine levels were selected in Shandong Province, China. These included a low, medium, and high iodine group and an iodine excess group whose water iodine content was < 10, 50-150, 150-300, and > 300 μg/L, respectively. Residents aged 20-65 years answered a questionnaire and underwent carotid artery ultrasonography, and their height, weight, and urinary iodine concentrations were measured. A total of 2026 individuals participated in the study. Urinary iodine concentration increased with increased water iodine levels. The medial thickening rate and intimal roughness rate in the iodine excess group were significantly higher than in the other three groups. After controlling for factors such as gender, age, and BMI, iodine excess remained as a risk factor for carotid intima-media thickening. Excess water iodine in the external environment is a risk factor for intima-media thickening of the carotid artery, suggesting that iodine excess may cause vascular injury and promote atherosclerosis.

Impact of urinary iodine concentration on blood glucose levels and blood pressure: a nationwide population-based study

PURPOSE

Iodine is a vital trace element for systemic metabolic control as well as thyroid hormone synthesis. Though iodine has significant antioxidant and anti-inflammatory effects, reports on its effects on metabolic disorders are limited and inconsistent.

METHODS

Impact of urinary iodine concentrations (UICs) on fasting blood glucose (FBG) levels and blood pressure (BP) in the general Korean population was evaluated adjusting for covariates including thyrotropin level and presence of thyroid diseases.

RESULTS

The median UIC was 302.3 μg/L in all participants and was significantly lower in those with dysglycemia (303.6 μg/L in normal participants, 285.1 μg/L in participants with FBG levels of 100-125 mg/dL, and 261.8 μg/L in participants with FBG levels ≥ 126 mg/dL; p = 0.002). Similarly, the UIC was lower in participants with higher BP (311.6 μg/L in normal participants, 288.7 μg/L in prehypertensive participants, and 265.8 μg/L in hypertensive participants; p < 0.001). The multiple linear regression model showed a negative correlation between the UIC and FBG levels (p = 0.002), and the UIC and systolic BP (p < 0.001). One standard deviation increase in the UIC showed odds ratios of 0.84 (95% confidence interval [CI] = 0.73-0.98) for elevated FBG levels (≥ 100 mg/dL) and 0.94 (95% CI = 0.88-0.99) for elevated SBP (≥ 120 mm Hg) after full adjustment.

CONCLUSION

Higher UICs were associated with lower FBG and BP levels, independent of thyroid function and other confounding factors in Korea, an iodine-replete country.