The Relationship between High Iodine Consumption and Levels of Autoimmune Thyroiditis-Related Biomarkers in a Chinese Population: a Meta-Analysis

Wan, Siyuan; Jin, Baiming; Ren, Bingxuan; Qu, Mengying; Wu, Hui; Liu, Lixiang; Boah, Michael; Shen, Hongmei

doi:10.1007/s12011-019-01951-9

Cited by 11 publications

(13 citation statements)

References 18 publications

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“…1). Under this respect, the last data from Danish and Sri Lanka surveys showing no increase of hypothyroidism incidence and a decrease of hyperthyroidism due to Graves' disease about two decades after starting iodoprophylaxis program are of particular interest, as well as the results of recent studies on Chinese populations [69,74,77]. As mentioned above, a "U-shaped" relationship between iodine intake and the risk of developing thyroid autoimmune disease is conceivable, namely, both iodine excess (even moderate) and also iodine deficiency may increase such risk [71].…”

Section: Discussionmentioning

confidence: 99%

“…More recently, in a study conducted in China after two decades of universal salt iodination program, a stable prevalence of thyroid antibody positivity in the population has been reported. This study also found an inverse relationship between iodine intake and thyroid antibodies, suggesting that UIC between 100 and 300 μg/L is optimal and safe for thyroid autoimmunity [ 69 ]. More specifically, a number of data suggest that only iodine supplementation regimens attaining relatively high median UIC levels (i.e., 200 µg/L or more) are able to induce relevant long-term alteration of thyroid function due to autoimmune disease, and the relationship between population iodine supply and occurrence of AITD could be depicted by a “U-shaped” function [ 70 , 71 ]: in other words, the likelihood of developing thyroid autoimmune diseases would increase when median population UIC exceeds approximately 300 µg/L, but as well when is less than 100 µg/L (see Fig.…”

Section: Does Iodoprophylaxis Induce Thyroid Autoimmunity?mentioning

confidence: 91%

“…1 ). The majority of these results come from Chinese populations, in whom marked differences in iodine supply in single region have been observed due to different iodine supply strategies [ 69 , 71 – 75 ]. In line with such a scenario, according to at least two recent reports cited above [ 58 , 59 ] both iodine deficiency and iodine excess are associated with increased risk of thyroid autoantibody positivity in pregnancy.…”

Section: Does Iodoprophylaxis Induce Thyroid Autoimmunity?mentioning

confidence: 99%

“…Therefore, monitoring iodoprophylaxis with standardized population surveys is mandatory, to ensure that both iodine deficiency and iodine excess are avoided. In this regard and on the basis of the experience from Italy and other countries [ 20 , 69 ], we are confident that the routine assessment of thyroid hypoechogenicity in monitoring iodine prophylaxis programs in populations will provide the advantage of easily and quickly identifying even minimal modifications of this frequency over time and to allow the appropriate adjustments of the iodine prophylaxis program if necessary.…”

Section: Does Iodoprophylaxis Induce Thyroid Autoimmunity?mentioning

confidence: 99%

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Iodoprophylaxis and thyroid autoimmunity: an update

Teti¹,

Panciroli

Nazzari

et al. 2021

Immunol Res

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Adequate iodine intake is necessary for normal thyroid function. Iodine deficiency is associated with serious complications, but also iodine excess can lead to thyroid dysfunction, and iodine supplementation aimed to prevent iodine deficiency disorders has been associated with development of thyroid autoimmunity. The epidemiology of thyroid diseases has undergone profound changes since the implementation of iodoprophylaxis, notably by means of iodine-enriched salt, specifically resulting in decreased prevalence of goiter and neonatal hypothyroidism, improved cognitive function development in infancy, and reduced incidence of more aggressive forms of thyroid cancer. The main question we address with this review is the clinical relevance of the possible effect on autoimmunity exerted by the use of iodine-enriched salt to correct iodine deficiency. In animal models, exogenous iodine is able to trigger or exacerbate thyroid autoimmunity, but it is still not clear whether the observed immunological changes are due to a direct effect of iodine on immune response, or whether they represent a secondary response to a toxic effect of iodine on thyroid tissue. Previous iodine status of a population seems to influence the functional thyroid response to increased iodine intake and possibly the development of thyroid autoimmunity. Moreover, the prevalence of thyroid antibodies, regarded as hallmark of autoimmune thyroid disease, varies between populations under the influence of genetic and environmental factors, and the presence of thyroid antibodies does not always coincide with the presence of thyroid disease or its future development. In addition, the incidence of autoimmune diseases shows a general increasing trend in the last decades. For all these reasons, available data are quite heterogeneous and difficult to analyze and compare. In conclusion, available data from long-term population surveys show that a higher than adequate population iodine intake due to a poorly controlled program of iodine prophylaxis could induce thyroid dysfunction, including thyroid autoimmunity mostly represented by euthyroid or subclinical hypothyroid autoimmune thyroiditis. Close monitoring iodine prophylaxis is therefore advised to ensure that effects of both iodine deficiency and iodine excess are avoided.

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Section: Discussionmentioning

confidence: 99%

Section: Does Iodoprophylaxis Induce Thyroid Autoimmunity?mentioning

confidence: 91%

Section: Does Iodoprophylaxis Induce Thyroid Autoimmunity?mentioning

confidence: 99%

Section: Does Iodoprophylaxis Induce Thyroid Autoimmunity?mentioning

confidence: 99%

See 2 more Smart Citations

Iodoprophylaxis and thyroid autoimmunity: an update

Teti¹,

Panciroli

Nazzari

et al. 2021

Immunol Res

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“…Causes of excess iodine are the consumption of overiodized salt, seaweeds (as already mentioned) [ 141 , 144 , 145 ], consumption of excess iodine through water and milk and taking diary supplements that contain iodine [ 234 ]. Most studies investigating the effect of high iodine intake on TSH and thyroid hormone levels in healthy adults observed an increase in TSH levels and a decrease in the levels of thyroid hormones after excess iodine [ 141 , 144 , 145 , 235 , 236 , 237 , 238 , 239 , 240 , 241 ]. Although only a few studies have been conducted, the pattern of TSH and thyroid hormone levels observed in these studies has shown consistency: an increase in TSH levels followed by a decrease in thyroid hormone levels ( Table 1 ).…”

Section: Environmental Factors That Influence Tsh and Thyroid Hormone Levelsmentioning

confidence: 99%

Environmental Factors Affecting Thyroid-Stimulating Hormone and Thyroid Hormone Levels

Leko

Gunjača

Pleić

et al. 2021

IJMS

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Thyroid hormones are necessary for the normal functioning of physiological systems. Therefore, knowledge of any factor (whether genetic, environmental or intrinsic) that alters the levels of thyroid-stimulating hormone (TSH) and thyroid hormones is crucial. Genetic factors contribute up to 65% of interindividual variations in TSH and thyroid hormone levels, but many environmental factors can also affect thyroid function. This review discusses studies that have analyzed the impact of environmental factors on TSH and thyroid hormone levels in healthy adults. We included lifestyle factors (smoking, alcohol consumption, diet and exercise) and pollutants (chemicals and heavy metals). Many inconsistencies in the results have been observed between studies, making it difficult to draw a general conclusion about how a particular environmental factor influences TSH and thyroid hormone levels. However, lifestyle factors that showed the clearest association with TSH and thyroid hormones were smoking, body mass index (BMI) and iodine (micronutrient taken from the diet). Smoking mainly led to a decrease in TSH levels and an increase in triiodothyronine (T3) and thyroxine (T4) levels, while BMI levels were positively correlated with TSH and free T3 levels. Excess iodine led to an increase in TSH levels and a decrease in thyroid hormone levels. Among the pollutants analyzed, most studies observed a decrease in thyroid hormone levels after exposure to perchlorate. Future studies should continue to analyze the impact of environmental factors on thyroid function as they could contribute to understanding the complex background of gene–environment interactions underlying the pathology of thyroid diseases.

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