Selenium and goiter prevalence in borderline iodine sufficiency

Selenium, Iodine and Iron-Essential Trace Elements for Thyroid Hormone Synthesis and Metabolism

The adequate availability and metabolism of three essential trace elements, iodine, selenium and iron, provide the basic requirements for the function and action of the thyroid hormone system in humans, vertebrate animals and their evolutionary precursors. Selenocysteine-containing proteins convey both cellular protection along with H₂O₂-dependent biosynthesis and the deiodinase-mediated (in-)activation of thyroid hormones, which is critical for their receptor-mediated mechanism of cellular action. Disbalances between the thyroidal content of these elements challenge the negative feedback regulation of the hypothalamus-pituitary-thyroid periphery axis, causing or facilitating common diseases related to disturbed thyroid hormone status such as autoimmune thyroid disease and metabolic disorders. Iodide is accumulated by the sodium-iodide-symporter NIS, and oxidized and incorporated into thyroglobulin by the hemoprotein thyroperoxidase, which requires local H₂O₂ as cofactor. The latter is generated by the dual oxidase system organized as 'thyroxisome' at the surface of the apical membrane facing the colloidal lumen of the thyroid follicles. Various selenoproteins expressed in thyrocytes defend the follicular structure and function against life-long exposure to H₂O₂ and reactive oxygen species derived therefrom. The pituitary hormone thyrotropin (TSH) stimulates all processes required for thyroid hormone synthesis and secretion and regulates thyrocyte growth, differentiation and function. Worldwide deficiencies of nutritional iodine, selenium and iron supply and the resulting endemic diseases are preventable with educational, societal and political measures.

Trace elements and the thyroid

Trace elements, such as iodine and selenium (Se), are vital to human health and play an essential role in metabolism. They are also important to thyroid metabolism and function, and correlate with thyroid autoimmunity and tumors. Other minerals such as iron (Ir), lithium (Li), copper (Co), zinc (Zn), manganese (Mn), magnesium (Mg), cadmium (Cd), and molybdenum (Mo), may related to thyroid function and disease. Normal thyroid function depends on a variety of trace elements for thyroid hormone synthesis and metabolism. These trace elements interact with each other and are in a dynamic balance. However, this balance may be disturbed by the excess or deficiency of one or more elements, leading to abnormal thyroid function and the promotion of autoimmune thyroid diseases and thyroid tumors.The relationship between trace elements and thyroid disorders is still unclear, and further research is needed to clarify this issue and improve our understanding of how trace elements mediate thyroid function and metabolism. This paper systematically reviewed recently published literature on the relationship between various trace elements and thyroid function to provide a preliminary theoretical basis for future research.

Using chemical fractionation and speciation to describe uptake of technetium, iodine and selenium by Agrostis capillaris and Lolium perenne

To understand the dynamic mechanisms governing soil-to-plant transfer of selenium (Se), technetium-99 (⁹⁹Tc) and iodine (I), a pot experiment was undertaken using 30 contrasting soils after spiking with ⁷⁷Se, ⁹⁹Tc and ¹²⁹I, and incubating for 2.5 years. Two grass species (Agrostis capillaris and Lolium perenne) were grown under controlled conditions for 4 months with 3 cuts at approximately monthly intervals. Native (soil-derived) ⁷⁸Se and¹²⁷I, as well as spiked ⁷⁷Se, ⁹⁹Tc and ¹²⁹I, were assayed in soil and plants by ICP-MS. The grasses exhibited similar behaviour with respect to uptake of all three elements. The greatest uptake observed was for ⁹⁹Tc, followed by ⁷⁷Se, with least uptake of ¹²⁹I, reflecting the transformations and interactions with soil of the three isotopes. Unlike soil-derived Se and I, the available pools of ⁷⁷Se, ⁹⁹Tc and ¹²⁹I were substantially depleted by plant uptake across the three cuts with lower concentrations observed in plant tissues in each subsequent cut. Comparison between total plant offtake and various soil species suggested that ⁷⁷SeO₄^2-, ⁹⁹TcO₄^- and ¹²⁹IO₃^-, in soluble and adsorbed fractions were the most likely plant-available species. A greater ratio of ¹²⁷I/¹²⁹I in the soil solid phase compared to the solution phase confirmed incomplete mixing of spiked ¹²⁹I with native ¹²⁷I in the soil, despite the extended incubation period, leading to poor buffering of the spiked available pools. Compared to traditional expressions of soil-plant transfer factor (TF_total), a transfer factor (TF_available) expressed using volumetric concentrations of speciated 'available' fractions of each element showed little variation with soil properties.

Selenium inadequacy hampers thyroid response of young children after iodine repletion

Selenium (Se) is an integral component of iodothyronine deiodinase, glutathione peroxidase and thioredoxin reductase enzymes and thus is important for normal thyroid function. This study investigated the influence of Se inadequacy on thyroid response of iodine-replete young children. Serum thyroxine (T₄), triiodothyronine (T₃), thyroglobulin (Tg), thyroid stimulating hormone (TSH), and Se were analyzed in 54-60 mo old children (n = 628) from the Amhara region of Ethiopia before salt iodization was commenced; analyses were repeated (n = 555) 15 mo after iodized salt became available. Iodized salt coverage increased from 12.2% to 91.6% of households. Median urinary iodine concentration (UIC) among children increased from 9 μg/l to 167 μg/l (p < 0.001). In addition, all thyroid indices except T₃ showed significant improvement (p < 0.05). Nearly, half of the study children (49.1%) had Se inadequacy (serum Se < 70 μg/l). Serum Se was significantly correlated with T₃ (r = 0.38, p < 0.001), T₄ (r = 0.15, p < 0.001), TSH (r=-0.205, p < 0.001) and Tg (r= -0.11, p < 0.01) concentrations 15 mo after iodine repletion; baseline serum Se and T₄(r= -0.22, p < 0.01) were inversely correlated. Despite adequate iodine status, children with low serum Se had lower serum T₄ (p = 0.003) and T₃(p < 0.001) but higher TSH concentration (p = 0.003). In the partial least square regression model, Se was among the latent variables significantly explaining T₄ and T₃. Results of the present study suggest that Se inadequacy negatively affects the thyroid metabolism of iodine-replete children and may present a substantial public health concern thus emphasize the need to consider correction of Se status for normal thyroid function as well as for benefits from its diverse biological roles.

Medical geology of endemic goiter in Kalutara, Sri Lanka; distribution and possible causes

This study assesses the distribution of goiter in the Kalutara District, Sri Lanka in order to find causative factors for the occurrence of goiter even after the salt iodization. A questionnaire survey was conducted at the household level and at the same time iodine and selenium levels of the water sources were analyzed. Questionnaire survey results indicated the highest numbers of goiter patients in the northern part where the lowest were found in the southern sector which may be due to the presence of acid sulfate soils. Females were more susceptible and it even showed a transmittance between generations. Average iodine concentrations in subsurface water of goiter endemic regions are 28.25 ± 15.47 μg/L whereas non-goiter regions show identical values at 24.74 ± 18.29 μg/L. Surface water exhibited relatively high values at 30.87 ± 16.13 μg/L. Endemic goiter was reported in some isolated patches where iodine and selenium concentrations low, latter was <10 μg/L. The formation of acid sulfate soils in the marshy lands in Kalutara district may lead to transformation of biological available iodine oxidation into volatile iodine by humic substances, at the same time organic matter rich peaty soil may have strong held of iodine and selenium which again induced by low pH and high temperature were suggested as the instrumental factors in the endemic goiter in Kalutara district. Hence, geochemical features such as soil pH, organic matter and thick lateritic cap in the Kalutara goiter endemic area play a role in controlling the available selenium and iodine for food chain through plant uptake and in water.

Poor dietary diversity, wealth status and use of un-iodized salt are associated with goiter among school children: a cross-sectional study in Ethiopia

Background

Globally, more than two billion people are at risk of iodine deficiency disorders, 32% of which are school children. Iodine deficiency has been recognized as a severe public health concern in Ethiopia, however little is known about the problem. Therefore, this study aimed to assess the prevalence of goiter and associated factors among school children (6 to 12 years) in Dabat District, northwest Ethiopia.

Methods

A school-based cross-sectional study was conducted from February 21 to March 31, 2016. A total of 735 school children were included in the study. A stratified multistage sampling followed by systematic sampling technique was employed to select the study participants. Thyroid physical examination was done and classified according to the World Health Organization recommendations as grade 0, grade 1, and grade 2. The level of salt iodine content was determined using the rapid field test kit. The value 0 parts per million (PPM), <15 PPM and ≥15 PPM with the corresponding color chart on the rapid test kit were used to classify the level of iodine in the sampled salt. A multivariable logistic regression analysis was employed to identify factors associated with goiter. Adjusted Odds Ratio (AOR) with a 95% Confidence Interval (CI) was calculated to show the strength of association. In multivariable analysis, variables with a P-value of <0.05 were considered statistically significant.

Results

In this community, the overall prevalence of goiter was 29.1% [95% CI: 25.9, 32.6], in which about 22.4 and 6.7% had goiter grade 1 and grade 2, respectively. The age of children (AOR = 1.13; 95% CI: 1.01, 1.26), being housewife mother (AOR = 1.49; 95% CI: 1.08, 2.15), use of unprotected well water source for drinking (AOR = 6.25; 95% CI: 2.50, 15.66), medium household wealth status (AOR = 1.78; 95% CI: 1.18, 2.92), use of inadequately iodized salt (AOR = 2.79; 95% CI: 1.86, 4.19), poor dietary diversity score of the child (AOR = 1.92;95% CI: 1.06, 3.48) and medium maternal knowledge (AOR = 0.65; 95% CI: 0.42, 0.94) were significantly associated with goiter.

Conclusions

The prevalence of goiter is higher in Dabat District, which confirmed a moderate public health problem. Therefore, regular monitoring of household salt iodine content, improving access to safe water, promoting the importance of diversified food for children is recommended to address the higher burden of iodine deficiency.

Ensuring Effective Prevention of Iodine Deficiency Disorders

BACKGROUND

Programs initiated to prevent iodine deficiency disorders (IDD) may not remain effective due to changes in government policies, commercial factors, and human behavior that may affect the efficacy of IDD prevention programs in unpredictable directions. Monitoring and outcome studies are needed to optimize the effectiveness of IDD prevention.

SUMMARY

Although the need for monitoring is compelling, the current reality in Europe is less than optimal. Regular and systematic monitoring surveys have only been established in a few countries, and comparability across the studies is hampered by the lack of centralized standardization procedures. In addition, data on outcomes and the cost of achieving them are needed in order to provide evidence of the beneficial effects of IDD prevention in countries with mild iodine deficiency.

CONCLUSION

Monitoring studies can be optimized by including centralized standardization procedures that improve the comparison between studies. No study of iodine consumption can replace the direct measurement of health outcomes and the evaluation of the costs and benefits of the program. It is particularly important that health economic evaluation should be conducted in mildly iodine-deficient areas and that it should include populations from regions with different environmental, ethnic, and cultural backgrounds.

A randomized-controlled, double-blind study of the impact of selenium supplementation on thyroid autoimmunity and inflammation with focus on the GPx1 genotypes

PURPOSE

To analyze the impact of selenium supplementation on serum antiTPO levels and thyroid echogenicity in patients with CAT, evaluating the response in subgroups with different GPx1 genotypes.

METHODS

CAT patients (n = 55) with positive antiTPO were randomized to selenomethionine (SeMet) 200 μg daily (n = 28) or placebo (n = 27) for 3 months. Assessments included GPx1 genotyping at baseline and serum levels of plasma selenium, erythrocyte GPx1 activity, antiTPO and thyroid echogenicity at baseline, and 3 and 6 months.

RESULTS

In the SeMet group, the increase in plasma levels of selenium and erythrocyte GPx1 activity was similar among patients with different GPx1 genotypes. In the overall cohort, patients randomized to SeMet showed a 5 % decrease in antiTPO levels at 3 months (p = non-significant) and 20 % at 6 months (p < 0.001 versus 3 months). In contrast, patients in the placebo group did not show significant changes in antiTPO levels at any time point. Subgroup analysis showed that patients with different GPx1 genotypes presented comparable responses in antiTPO levels and echogenicity index to SeMet.

CONCLUSIONS

Selenium supplementation decreased serum antiTPO levels in CAT patients, with similar response among patients with different GPx1 genotypes.

Selenium and the thyroid

PURPOSE OF REVIEW

This article provides an update on the role of the essential trace element selenium and its interaction with the other trace elements iodine and iron that together contribute to adequate thyroid hormone status. Synthesis, secretion, metabolism and action of thyroid hormone in target tissues depend on a balanced nutritional availability or supplementation of these elements. Selenium status is altered in benign and malignant thyroid diseases and various selenium compounds have been used to prevent or treat widespread diseases such as goiter, autoimmune thyroid disease or thyroid cancer.

RECENT FINDINGS

Several studies, most with still too low numbers of cases, indicate that selenium administration in both autoimmune thyroiditis (Hashimoto thyroiditis) and mild Graves' disease improves clinical scores and well-being of patients and reduces thyroperoxidase antibody titers. However, published results are still conflicting depending on basal selenium status, dose, time and form of selenium used for intervention. Evidence for sex-specific selenium action, lack of beneficial effects in pregnancy and contribution of genetic polymorphisms (selenoprotein S) has been presented.

SUMMARY

Adequate nutritional supply of selenium that saturates expression of circulating selenoprotein P, together with optimal iodine and iron intake, is required for a healthy and functional thyroid during development, adolescence, adulthood and aging.

Selenium: an element for life

This review aims to illustrate the importance of selenium (Se) for maintenance of overall health, especially for the thyroid, immunity, and homeostasis. Furthermore, it outlines the role of Se in reproduction and in virology and discusses the effects of Se supplementation in critical illness. The multifaceted aspects of this essential nutrient have attracted worldwide clinical and research interest in the last few decades. Se exerts its activity in the form of the aminoacid selenocysteine incorporated in selenoproteins. The impact of Se administration should be considered in relation to its apparent U shaped effects, i.e., exhibiting major advantages in Se-deficient individuals but specific health risks in those with Se excess. Addition of selenium to the administration of levothyroxine may be useful in patients with low Se intake and with mild-form or early-stage Hashimoto's thyroiditis (HT). Serum Se concentration (possibly also at tissue level) decreases in inflammatory conditions and may vary with the severity and duration of the inflammatory process. In such cases, the effect of Se supplementation seems to be useful and rational. Meanwhile, Se's ability to improve the activity of T cells and the cytotoxicity of natural killer cells could render it effective in viral disease. However, the evidence, and this should be stressed, is at present conflicting as to whether Se supplementation is of benefit in patients with HT, though there are indications that it is advantageous in cases of mild/moderate Graves' Orbitopathy. The role of Se in type 2 diabetes mellitus (T2DM) is ambiguous, driven by both Se intake and serum levels. The evidence that insulin and glycaemia influence the transport and activity of Se, via regulatory activity on selenoproteins, and that high serum Se may have a diabetogenic effect suggests a 'Janus-effect' of Se in T2DM. Though the evidence is not as yet clear-cut, the organic form (selenomethionine), due to its pharmacokinetics, is likely to be more advantageous in long-term prevention, and supplementation efforts, while the inorganic form (sodium selenite) has proven effective in an acute, e.g., sepsis, clinical setting. Recent data indicate that functional selenoprotein single-nucleotide polymorphisms (SNPs) may interfere with Se utilization and effectiveness.

The Association between Cobalt Deficiency and Endemic Goiter in School-Aged Children

BACKGROUND

In Iran, an iodine deficiency control program was initiated in 1989 by iodizing salt. Despite this program, goiters have remained an endemic condition in most parts of Iran. Thus, it is possible that other factors aside from iodine deficiency may contribute to endemic goiter. The aim of this study was to investigate the association between cobalt deficiency and endemic goiter in a region of Iran with a high prevalence of goiter.

METHODS

A cross-sectional study was conducted among school children aged 9 to 11 years in the city of Kerman, Iran. In the first phase of the study, a multistage, proportional-to-size, cluster sampling method was used to screen 5,380 out of 29,787 students. After the screening phase, 170 students (130 goitrous and 40 nongoitrous) were randomly selected, and serum and urine specimens were obtained. We measured thyroid function, serum cobalt level, and urinary iodine excretion. Univariate and multiple logistic regression analyses were performed.

RESULTS

The prevalence of grade 2 goiters was 34.8% (95% confidence interval [CI], 31.5 to 42.5), with both sexes being equally affected. The weight and body mass index of goitrous subjects was significantly lower (P<0.001) than those of nongoitrous subjects. The serum cobalt levels were lower in goitrous subjects than in nongoitrous subjects (4.4±2.9 µg/L vs. 6.4±2.7 µg/L). The urinary iodine levels were also lower in goitrous subjects than in nongoitrous subjects (198.3±108.3 µg/L vs. 270.2±91.1 µg/L). Multiple regression analysis showed that only cobalt deficiency, not iodine deficiency, significantly contributed to the presence of goiter (odds ratio, 0.78; 95% CI, 0.61 to 0.99; P=0.042).

CONCLUSION

Cobalt deficiency may be an important independent predicator for goiter in endemic regions, especially areas in which goiters persist despite salt iodization programs.

Genetic and non-iodine-related factors in the aetiology of nodular goitre

Genetic and a large number of environmental non-iodine-related factors play a role in the cause of nodular goitre. Most evidence for the influence of genetic and environmental factors in the cause of goitre is from cross-sectional, population-based studies. Only a few studies have included prospective data on risk factors for nodular goitre, although few prospective data are available on the effect of iodine and tobacco smoking on goitre development. Goitre is not one single phenotype. Many epidemiological studies do not distinguish diffuse from nodular goitre, as the investigated parameter is often thyroid volume or frequency with increased thyroid volume. Moreover, information on the presence and effect of gene-environment, gene-gene, and environment-environment effect modifications is limited. Thus, firm conclusions about the relative contributions and causality of the investigated risk factors should be made with caution. Smoking seems to be an established risk factor for nodular goitre, possibly with effect modification from iodine intake, as the risk associated with smoking is smaller or absent in areas with sufficient iodine intake. The use of oral contraceptives might have protective effects against goitre, and childbirth is an increased risk factor for goitre in areas with non-optimal iodine intake. Insulin resistance is a recently investigated risk factor, and the risk of goitre may be reversible with metformin treatment. Iodine remains the major environmental risk factor for nodular goitre.

Thyroid volume, goiter prevalence, and selenium levels in an iodine-sufficient area: a cross-sectional study

Background

Selenium (Se) is a necessary element for the biosynthesis of thyroid hormones. We investigated the relationship between selenium status, thyroid volume, and goiter in a cross-sectional study in an iodine-sufficient area.

Methods

We selected residents of Chengdu (over 18 years old and living in the city for more than 5 years) using a stratified cluster sampling technique. Fifteen hundred subjects were selected for the study, which involved a questionnaire survey, physical examination, thyroid ultrasound, serum thyroid function test, and determination of serum selenium level. Thyroid volume was calculated from the thickness, width, length, and a corrective factor for each lobe. Ultimately, 1,205 subjects completed the investigation and were included in our study. Additionally, 80 school-age children were selected to provide urine samples for urinary iodine analysis. We analyzed the data using appropriate nonparametric and parametric statistical tests.

Results

The median urinary iodine value was 184 μg/L in school-age children, indicating iodine sufficiency. The median serum selenium level of the 1,205 subjects was 52.63 (interquartile range [IQR] : 40.40-67.00) μg/L. The median thyroid volume was 9.93 (IQR: 7.71-12.57) mL; both log-transformed serum selenium and log-transformed thyroid volume were Gaussian distributions (P = .638 and P = .046, respectively). The prevalences of goiter and thyroid nodules were 8.8% and 18.6%. The prevalences of positive thyroid autoantibodies, thyroperoxidase autoantibodies and thyroglobulin autoantibodies were 16.7%, 12.0%, and 11.1%, respectively. In the general linear regression model, there were positive associations between serum selenium and age, and body mass index. We found no association between serum selenium and thyroid-stimulating hormone. In simple linear regression analyses, we found no association between thyroid volume and serum selenium. There were no significant differences in serum selenium between persons with or without goiter. Serum selenium was not a risk factor for goiter.

Conclusion

In our study population, serum selenium was neither associated with thyroid volume nor with goiter in an iodine-sufficient area. More studies should be conducted by following non-goitrous persons over time and monitoring their selenium status.

Selenium and the thyroid

PURPOSE OF REVIEW

To provide information on the role of the essential trace element selenium, which enables appropriate thyroid hormone synthesis, secretion, and metabolism, and to discuss supplementation with various selenium compounds, which prevent thyroid diseases such as goiter and exert beneficial effects in thyroid autoimmune diseases.

RECENT FINDINGS

Selenium administration in both autoimmune thyroiditis (M. Hashimoto) and mild Graves' disease improves clinical scores and well-being of patients and reduces autoimmune antibody titres in several prospective, placebo-controlled supplementation studies.

SUMMARY

Adequate nutritional supply of selenium, together with the two other essential trace elements iodine and iron, is required for a healthy thyroid during development and adolescence, as well as in the adult and aging populations.

Approach to and treatment of goiters

The main causes of simple diffuse goiter (SDG) and multinodular goiter (MNG) are iodine deficiency, increase in serum thyroid-stimulating hormone (TSH) level, natural goitrogens, smoking, chronic malnutrition, and lack of selenium, iron, and zinc. Increasing evidence suggests that heredity is equally important. Treatment of SDG and MNG still focuses on L-thyroxine-suppressive therapy surgery. Radioiodine alone or preceded by recombinant human TSH stimulation is widely used in Europe and other countries. Each of these therapeutic options has advantages and disadvantages, with acute and long-term side effects.

Effect of Selenium on HLA-DR Expression of Thyrocytes

Autoimmune thyroid diseases (ATDs) represent the most frequent forms of the organ-specific autoimmune thyroid disorders that result from interaction between genetic and environmental factors. Selenium has been shown to exert a beneficial effect on the autoimmune thyroiditis. In spite of therapeutical effect of selenium on autoimmunity, the mechanism of its action has not been revealed. Objective. To determine whether selenium in vitro thyrocytes cultures are able to influence the HLA-DR molecule expression of human thyrocytes and production of free oxygen radicals. Method. Thyrocytes were prepared from human thyroid gland and cultured in vitro in the presence of interferon-γ and sodium selenite. The expression of HLA-DR molecules induced by interferon-γ in the presence of sodium selenite of various concentration was measured by fluorescence-activated cell sorter. Results. Selenium has a dose-dependent inhibitory effect on the expression of HLA-DR molecules of thyrocytes induced by interferon-γ. This effect of selenium was in the inverse correlation with antioxidative capacity. Conclusion. Beneficial effect of selenium on autoimmune mechanism is a complex mechanism in which the inhibitory effect on HLA-DR molecule expression and antioxidative capacity are involved into therapy of autoimmune thyroiditis.

Evaluation of iodine, iron, and selenium in biological samples of thyroid mother and their newly born babies

BACKGROUND

There is accumulating facts that the metabolism of essential trace elements is altered in thyroid patients.

AIM

The aim of present study was to compare the status of essential trace elements, iodine, iron (Fe), and selenium (Se) in biological samples (serum and urine) of goitrous mothers (age ranged 30-40) and their newly born infants (n=76). An age matched 68 non-goitrous mothers and their infants, residing in the same locality, were selected as referents. For a comparative study, the biological samples of non-goitrous and goitrous pregnant and non pregnant female subjects of the same age group and socio-economic status were also analyzed.

METHODS

The Fe and Se concentrations in biological samples were determined by a flame and hydride generation atomic absorption spectrometry respectively, while iodine was measured by iodide-ion selective electrode, prior to microwave assisted acid digestion. The validity and accuracy of the methodology was checked by certified reference materials.

RESULTS

The mean values of iodine, Fe and Se in serum and urine samples of thyroid mothers and their infants were significantly lower as compared to the referent mothers-infants pairs (p<0.01).

CONCLUSIONS

The deficiencies of essential trace elements may adversely affect the health of women and their neonates.

Prevalence of age-related cataract in high-selenium areas of China

The objective of this study was to determine the prevalence of age-related cataract in high-selenium areas of China. This is a cross-sectional study of 1,522 persons aged 50 years and more who were selected as a representative sample from the Enshi prefecture in Hubei province. All lenses were graded and classified for opacities by slit lamp after papillary dilation, using the Lens Opacification Classification System II. The age-related cataract patients were 418 cases (33.28%). The prevalence of age-related cataract was 37.2% in women and 26.0% in men. The prevalence of nuclear cataract was 23.7%; cortical cataract was 22.4% and posterior subcapsule cataract was 5.2%. The prevalence of cataract of the 50-59 group was 13.41%; 60-69 group was 42.15%; 70 and over group was 61.9%. The prevalence of age-related cataract in high-selenium areas has not significantly increased; to some extent, the high selenium intake will not become a risk factor for the increase of cataract incidence.

Selenium deficiency as a possible contributor of goiter in schoolchildren of Isfahan, Iran

The prevalence of goiter still remains high in some areas of Iran in spite of iodine supplementation. In the present study, we investigated the role of selenium (Se) deficiency in the etiology of goiter in Isfahan. Two thousand three hundred thirty-one schoolchildren were selected by multistage random sampling. Thyroid size was estimated in each child by inspection and palpation. Urinary iodine concentration (UIC) and plasma Se were measured. Overall, 32.9% of the 2,331 children had goiter. The median UIC was 19.55 microg/dl. Plasma Se was measured in 96 goitrous and 72 nongoitrous children. The mean +/- SD of plasma Se in goitrous and nongoitrous children was 66.86 +/- 21.82 and 76.67 +/- 23.33 microg/l, respectively (P = 0.006). Goitrous girls had lower plasma Se level than nongoitrous girls (65.62 +/- 21.64 vs. 76.51 +/- 22.61 microg/dl, P = 0.02). Goitrous boys had lower plasma Se level than nongoitrous boys (68.45 +/- 22.21 vs. 76.91 +/- 24.76 microg/l, P = 0.14). The prevalence of Se deficiency was significantly higher in goitrous boys and girls than nongoitrous children. Se deficiency is among the contributors of goiter in Isfahan goitrous schoolchildren. However, the role of other micronutrient deficiencies or goitrogens should be investigated in this region.

Iodine-deficiency disorders

2 billion individuals worldwide have insufficient iodine intake, with those in south Asia and sub-Saharan Africa particularly affected. Iodine deficiency has many adverse effects on growth and development. These effects are due to inadequate production of thyroid hormone and are termed iodine-deficiency disorders. Iodine deficiency is the most common cause of preventable mental impairment worldwide. Assessment methods include urinary iodine concentration, goitre, newborn thyroid-stimulating hormone, and blood thyroglobulin. In nearly all countries, the best strategy to control iodine deficiency is iodisation of salt, which is one of the most cost-effective ways to contribute to economic and social development. When iodisation of salt is not possible, iodine supplements can be given to susceptible groups. Introduction of iodised salt to regions of chronic iodine-deficiency disorders might transiently increase the proportion of thyroid disorders, but overall the small risks of iodine excess are far outweighed by the substantial risks of iodine deficiency. International efforts to control iodine-deficiency disorders are slowing, and reaching the third of the worldwide population that remains deficient poses major challenges.

[The effect of selenium therapy on autoimmune thyroiditis]

Selenium as an essential trace element is capable of exerting complex effects on the endocrine and immune system by its antioxidant capacity. The role of selenium is important because the level of free oxygen radicals is elevated in the physiological thyroid hormone synthesis.

THE AIM OF STUDY

was to determine whether selenium therapy can influence the level of antithyroid peroxidase and antithyroglobulin antibodies or whether there is a correlation between antioxidant capacity and the titer of autoantibodies.

METHOD

132 patient with autoimmune thyroiditis were investigated in a prospective, blind and placebo-controlled study. L-thyroxine substitution therapy was made in both groups and the level of TSH remained in the normal range. The selenium-treated group (n = 70 patients, 68 female, mean age 41,4 +/- 9,5 year) was compared with the placebo-treated group (n = 62 patients, 61 female, mean age 42,7 +/- 8,3 year). Selenium therapy was continued by L-seleno-methionine (per os 2 x 100 microg/day) for one year. Determination of TSH, fT4, fT3 and autoantibodies was carried out by chemiluminescence method. Total antioxidant capacity was determined by Randox kit, the level of selenium in the sera by atomic absorption technique was measured. In the follow-up study, patients were controlled every third month and at the end of a one-year observation period.

RESULTS

The level of selenium in the untreated patients was significantly lower than in treated patients and controls. The fT3/fT4 ration proved to be higher in patients after selenium therapy. The titer of antithyroid antibodies (mostly the antithyroid peroxidase) significantly decreased at the end of the study. An inverse correlation was found between antioxidant capacity and the level of antithyroid peroxidase antibodies. The volume of thyroid gland slightly diminished in treated patients. Side effects were not observed.

CONCLUSIONS

Selenium completed with L-thyroxine is a suitable therapy for patients with autoimmune thyroiditis.

A practical approach to managing the risks of iodine deficiency in flocks using thyroid - weight: birthweight ratios of lambs

AIM

To establish a protocol for determining the iodine status of a flock and managing the risks of iodine deficiency, using thyroid-weight:birthweight ratios of newborn lambs and serum iodine concentrations of ewes.

METHODS

Data were collected from iodine supplementation studies in Southland and Rangitikei, of sheep fed exclusively pasture or pasture plus brassica during the latter half of gestation (n=350, or 89 per treatment group). The ewes were supplemented pre-mating or at the time of pregnancy scanning with an injection of long-acting iodised oil. Serum iodine concentrations were measured in ewes prepartum in Rangitikei and postpartum at both locations. The thyroid-weight:birthweight ratios (as g/ kg) in 229 newborn lambs were determined at post-mortem examination and compared between iodine supplemented vs unsupplemented flocks using probit analysis. Samples of pasture and kale were analysed monthly for determination of iodine and selenium.

RESULTS

Initial mean serum iodine concentration of all ewes was 41 mug iodine/L. Supplementation increased serum iodine concentrations regardless of forage fed, and concentrations remained high for between 127 and 206 days. The range of thyroid-weight:birthweight ratios in lambs from supplemented ewes was 0.09-0.70 (mean 0.35, standard deviation (SD) 0.147) g/kg. Among lambs from unsupplemented ewes, the range was much wider (0.21-8.5; mean 1.61, SD 1.95 g/kg). About half of those ratios were >0.8 g/kg and clearly indicative of goitre, including 62% from the groups on brassica and 18% from the Rangitikei group fed exclusively pasture. Probit calculations showed that a ratio of 0.40 (95% confidence interval (CI)=0.29-0.47) g/kg predicted with 35% probability, and a ratio of 0.80 (95% CI=0.70-0.99) g/kg predicted with 90% probability that a lamb came from an unsupplemented flock.

CONCLUSIONS

Compared to iodine concentrations in forages, thyroid-weight:birthweight ratios more accurately reflected the iodine status of the flock and could be used to identify which flocks to supplement the following year. Serum iodine concentrations of ewes measured before or after lambing did not reflect forage fed, but values near 40 mug/L were associated with goitrous lambs.

CLINICAL RELEVANCE

Thyroid-weight:birthweight ratios >0.8 g/kg were indicative of iodine deficiency, and ewes should be supplemented pre-mating or during pregnancy to prevent goitre the following year. Ratios <0.4 g/kg rarely occurred among deficient flocks, so the probability of benefit from supplementation was low. Intermediate ratios were ambiguous, and the iodine status of the flock could not be determined from biomarkers. In such cases individual-farm supplementation trials might be required to detect and manage the risks of marginal deficiency.

Effect of age on sexually dimorphic selenoprotein expression in mice

Clinical data suggest that selenium (Se) supplementation decreases disease predisposition and severity and accelerates recovery in a variety of pathologies. Pre-supplementation Se levels and sex represent important determinants of these Se-dependent health effects. Accordingly, we previously reported on sexually dimorphic expression patterns of Se-dependent glutathione peroxidase 1, type I deiodinase, and selenoprotein P in young mice. In the present study we investigated whether these differences vary with age. The strong sexual dimorphic expression of hepatic type I deiodinase that was observed in young mice vanished both at the mRNA and enzyme activity level by 1 year of age. In contrast, the strong sex-specific differences in renal type I deiodinase mRNA expression were sustained with age. Accordingly, deiodinase enzymatic activities differed in male and female kidneys, largely independent of age [average of 6.8 vs. 15.7 pmol/(min mg) in males vs. females]. In parallel, hepatic Se concentrations and glutathione peroxidase activities increased in female mice compared to male littermates, establishing a new sexual dimorphism in liver. Thus, age represents another important modifier of the dynamic sex- and tissue-specific selenoprotein expression patterns. These data highlight again the unique physiological regulatory mechanisms that have evolved to control Se metabolism according to the actual needs of the organism.