Effects of chronic iodine excess in a cohort of long-term American workers in West Africa

Risks of Iodine Excess

Iodine is a micronutrient that is required for thyroid hormone synthesis. The iodide cycle in thyroid hormone synthesis consists of a series of transport, oxidation, organification, and binding/coupling steps in thyroid follicular cells. Common sources of iodine include the consumption of an iodine-rich diet or iodine fortified foods, the administration of amiodarone, iodine-containing supplements, or iodinated contrast media, and other miscellaneous sources. Methods to assess population iodine status include the measurement of urinary iodine concentrations, blood thyroglobulin levels, prevalence of elevated neonatal TSH levels, and thyroid volume. Although excessive iodine intake or exposure is generally well tolerated, an acute iodine load may result in thyroid dysfunction (hypothyroidism or hyperthyroidism) in certain susceptible individuals due to the failure to escape from the Wolff-Chaikoff effect and to the Jod-Basedow phenomenon, respectively. In this review, we discuss the associations between excessive iodine intake or exposure, with particular focus on iodinated contrast media as a common source of excess iodine in healthcare settings, and risks of incident thyroid dysfunction. We also summarize the risks of iodine excess in vulnerable populations and review current guidelines regarding the screening and monitoring of iodinated contrast-induced thyroid dysfunction. Finally, we discuss the long-term potential nonthyroidal health risks associated with iodine excess and suggest the need for more data to define safe upper limits for iodine intake, particularly in high-risk populations.

ESPEN practical short micronutrient guideline

BACKGROUND

Trace elements and vitamins, named together micronutrients (MNs), are essential for human metabolism. The importance of MNs in common pathologies is recognized by recent research, with deficiencies significantly impacting the outcome.

OBJECTIVE

This short version of the guideline aims to provide practical recommendations for clinical practice.

METHODS

An extensive search of the literature was conducted in the databases Medline, PubMed, Cochrane, Google Scholar, and CINAHL for the initial guideline. The search focused on physiological data, historical evidence (for papers published before PubMed release in 1996), and observational and/or randomized trials. For each MN, the main functions, optimal analytical methods, impact of inflammation, potential toxicity, and provision during enteral or parenteral nutrition were addressed. The SOP wording was applied for strength of recommendations.

RESULTS

The limited number of interventional trials prevented meta-analysis and led to a low level of evidence for most recommendations. The recommendations underwent a consensus process, which resulted in a percentage of agreement (%): strong consensus required of >90 % of votes. Altogether the guideline proposes 3 general recommendations and specific recommendations for the 26 MNs. Monitoring and management strategies are proposed.

CONCLUSION

This short version of the MN guideline should facilitate handling of the MNs in at-risk diseases, whilst offering practical advice on MN provision and monitoring during nutritional support.

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 Supplementation Improved Antioxidant Status, Hormonal Status, Sexual Behavior, and Semen Production Performance of Bos indicus Bulls Under Tropical Climatic Condition

Iodine is anessential micronutrient that plays a crucial role in male reproduction (sexual behavior and semen production performance) by modulating thyroid function and the antioxidant status of the animal. Nonetheless, in Bos indicus bulls, a thorough evaluation of the effects of dietary iodine supplementation on antioxidant status, seminal quality parameters, and its interaction with other minerals is not documented. Twelve Bos indicus (Sahiwal) bulls were distributed into three groups (n = 4 in each group) viz. T₁ (control), T₂, and T₃ and fed diets containing 0.250, 0.375, and 0.500 ppm iodine/ kg dry matter intake, corresponding to 0%, 50%, and 100% higher than ICAR (2013) recommendations, respectively. The experimental feeding was carried out for 60 days and the effects on nutrient utilization, hormonal and antioxidant status, and sperm function tests were investigated. Results revealed that body weight, dry matter intake, and nutrient digestibility remained unaffected by dietary supplementation of iodine. Testosterone and thyroxine hormone concentrations were improved (p<0.05) in T₂ and T₃ groups. Blood and seminal iodine content were also higher (p<0.05) in both the supplemented groups (T₂ and T₃). Sperm functions viz. viability, physical membrane integrity, acrosomal integrity, motility, and mitochondrial membrane potential were improved (p<0.05) due to iodine supplementation. Furthermore, lipid peroxidation and membrane scrambling in spermatozoa were reduced (p<0.05) in T₂ and T₃ groups. Blood antioxidant status (total antioxidant activity and GPx levels) was improved (p<0.05) in T₂ and T₃. Sexual behavior was also improved (p<0.05) in iodine-supplemented groups. Hence, it can be concluded that iodine supplementation at the dose rate of 0.500 ppm in the Bos indicus bull diet is beneficial in improving hormonal status, antioxidant status, and semen quality.

ESPEN micronutrient guideline

BACKGROUND

Trace elements and vitamins, named together micronutrients (MNs), are essential for human metabolism. Recent research has shown the importance of MNs in common pathologies, with significant deficiencies impacting the outcome.

OBJECTIVE

This guideline aims to provide information for daily clinical nutrition practice regarding assessment of MN status, monitoring, and prescription. It proposes a consensus terminology, since many words are used imprecisely, resulting in confusion. This is particularly true for the words "deficiency", "repletion", "complement", and "supplement".

METHODS

The expert group attempted to apply the 2015 standard operating procedures (SOP) for ESPEN which focuses on disease. However, this approach could not be applied due to the multiple diseases requiring clinical nutrition resulting in one text for each MN, rather than for diseases. An extensive search of the literature was conducted in the databases Medline, PubMed, Cochrane, Google Scholar, and CINAHL. The search focused on physiological data, historical evidence (published before PubMed release in 1996), and observational and/or randomized trials. For each MN, the main functions, optimal analytical methods, impact of inflammation, potential toxicity, and provision during enteral or parenteral nutrition were addressed. The SOP wording was applied for strength of recommendations.

RESULTS

There was a limited number of interventional trials, preventing meta-analysis and leading to a low level of evidence. The recommendations underwent a consensus process, which resulted in a percentage of agreement (%): strong consensus required of >90% of votes. Altogether the guideline proposes sets of recommendations for 26 MNs, resulting in 170 single recommendations. Critical MNs were identified with deficiencies being present in numerous acute and chronic diseases. Monitoring and management strategies are proposed.

CONCLUSION

This guideline should enable addressing suboptimal and deficient status of a bundle of MNs in at-risk diseases. In particular, it offers practical advice on MN provision and monitoring during nutritional support.

Stopping the supply of iodized salt alone is not enough to make iodine nutrition suitable for children in higher water iodine areas: A cross-sectional study in northern China

BACKGROUND

For the sake of children's health, iodized salt supply has been stopped in many areas with excessive iodine in the drinking water, but children's iodine nutrition status and thyroid function after terminating the iodized salt supply is unknown. Objective We assessed the iodine nutrition, thyroid function and influencing factors for thyroid abnormalities in children from areas with different concentrations of water iodine; the supply of iodized salt has been stopped in high water iodine areas. This study aimed to evaluate whether the strategy of stopping the supplies of iodized salt alone is enough to avoid thyroid dysfunction in all areas with excess water iodine while still meeting the iodine nutrition needs of children.

METHODS

A cross-sectional study was conducted in children from four areas with different drinking water iodine concentrations in Tianjin, China. The drinking water samplings and spot urine samples were collected to estimate the external and internal iodine exposure levels. The thyroid volume was measured, and blood samples were collected to assess thyroid function. Logistic regression analysis was used to analyze risk factors for thyroid abnormalities. A dietary survey was conducted to determine the sources of iodine nutrition among the areas with different iodine concentrations in the drinking water.

RESULTS

In the area with a drinking water iodine concentration ≥300 μg/L, the median urinary iodine concentration (UIC) in children was 476.30 (332.20-639.30) μg/L, which was higher than that in other groups (all P < 0.05), and the prevalence of thyroid nodules and the thyroid goiter rate were higher than those in the <100 μg/L, 100-150 μg/L and 150-300 μg/L areas (all P < 0.01). Binary logistic regression analysis indicated that the risk of thyroid abnormalities was significantly increased in the UIC 200-299 μg/L group (OR: 4.534; 95% CI: 1.565, 13.135; bootstrapped 95% CI: 1.689, 21.206, P = 0.004) and in the UIC ≥ 300 μg/L group (OR: 6.962; 95% CI: 2.490, 19.460; bootstrapped 95% CI: 2.838, 32.570, P = 0.001) compared to the 100-199 μg/L group. The iodine contribution rates from water in areas with water iodine concentrations ≥300 μg/L are up to 63.04%.

CONCLUSIONS

After termination of the iodized salt supply, the level of iodine nutrition of children in the area with drinking water iodine concentrations ≥300 μg/L is still excessive. The water source needs to be replaced in this area. In the area with a water iodine concentration of 150-300 μg/L, it is proposed that stopping the supply of iodized salt is sufficient to achieve the proper iodine nutrition status in children.

Risks of excess iodine intake in Ghana: current situation, challenges, and lessons for the future

In Ghana, iodine deficiency was first reported in 1994 among 33% of the population. A nationwide Universal Salt Iodization (USI) program plus other complementary interventions were subsequently implemented as a response. Our paper reviews the current risks of excess iodine status in Ghana and identifies policy and research gaps. A mixed methods review of 12 policies and institutional reports and 13 peer-reviewed articles was complemented with consultations with 23 key informants (salt producers and distributors, food processors, regulatory agency officials, and healthcare providers) purposively sampled between May and August 2017. The findings show a strong policy environment indicated by regulations on food and salt fortification (Act 851), including the USI regulation. However, currently, only a third of Ghanaian households use adequately iodized salt. Recent evidence shows that voluntarily fortified processed foods (including condiments) supply a considerable amount of iodine to the food system. Limited biological impact data suggest possible household exposure to excessive dietary iodine (>15 parts per million). Currently, there is no systematic tracking of iodine content from fortified foods and other sources. Cross-sectoral actions are needed to understand this situation better. Key research gap is the lack of comprehensive data on iodine content and intake from other sources in Ghana.

Excess iodine intake: sources, assessment, and effects on thyroid function

Iodine is essential for thyroid hormone synthesis. High iodine intakes are well tolerated by most healthy individuals, but in some people, excess iodine intakes may precipitate hyperthyroidism, hypothyroidism, goiter, and/or thyroid autoimmunity. Individuals with preexisting thyroid disease or those previously exposed to iodine deficiency may be more susceptible to thyroid disorders due to an increase in iodine intake, in some cases at intakes only slightly above physiological needs. Thyroid dysfunction due to excess iodine intake is usually mild and transient, but iodine-induced hyperthyroidism can be life-threatening in some individuals. At the population level, excess iodine intakes may arise from consumption of overiodized salt, drinking water, animal milk rich in iodine, certain seaweeds, iodine-containing dietary supplements, and from a combination of these sources. The median urinary iodine concentration (UIC) of a population reflects the total iodine intake from all sources and can accurately identify populations with excessive iodine intakes. Our review describes the association between excess iodine intake and thyroid function. We outline potential sources of excess iodine intake and the physiological responses and consequences of excess iodine intakes. We provide guidance on choice of biomarkers to assess iodine intake, with an emphasis on the UIC and thyroglobulin.

Does iodine excess lead to hypothyroidism? Evidence from a case-control study in India

BACKGROUND

Iodine deficiency disorders have been known to mankind since antiquity and various researchers elucidated the role of iodine in its causation. However, recent evidence shows that the entire control program ignored multi-causality and association of increased iodine intake with hypothyroidism. This study was conducted to assess differences of iodine intake as measured by urinary iodine excretion (UIE) between cases of hypothyroidism and healthy controls.

METHODS

A case-control study was conducted with three groups (cases, hospital controls and community controls) in two cities of India. Patients with overt hypothyroidism were cases (n = 150) and were compared with age, sex and socioeconomic status-matched hospital (n = 154) and community (n = 488) controls. Thyroid function tests (T3, T4, TSH) were used as diagnostic and inclusion criteria. TPOAb and UIE estimation were carried out for all study participants.

RESULTS

Mean values of TPOAb and UIE were higher in cases as compared to hospital controls as well as community controls (p <0.05). With a cut off of 34 IU/mL for TPOAb, more cases had an anti-TPO level >34 as compared to hospital controls (p <0.001) as well as community controls (p <0.001); OR, 0.06 (95% CI, 0.03, 0.12) and 0.08 (0.05, 0.12), respectively. For UIE cut-off of 300 μg/L, more cases than hospital controls (p = 0.090) and community controls (p = 0.001) had higher levels; OR, 0.671, (0.422, 1.066) and 0.509, (0.348, 0.744), respectively.

CONCLUSION

The study has clearly shown that cases of hypothyroidism are associated with excess iodine intake. Cohort studies to generate further evidence and an eco-social epidemiological approach have been suggested as the way forward.

Prevalence of goiter and thyroid nodules before and after implementation of the universal salt iodization program in mainland China from 1985 to 2014: a systematic review and meta-analysis

OBJECTIVES

We comprehensively estimated the prevalence of goiter and thyroid nodules (TNs) before and after the implementation of the Universal Salt Iodization (USI) program in mainland China and provided information for creating effective health policies.

METHODS

PubMed, Google Scholar, CNKI, Chinese Wanfang and Chongqing VIP databases were searched for relevant studies from Jan 1985 to Feb 2014. Data from eligible citations were extracted by two independent reviewers. All analyses were performed with Stata 11.0 and SPSS 17.0.

RESULTS

Eligible articles (N = 31; 4 in English and 27 in Chinese) included 52 studies (15 about goiter rates made before 1996 and 14 afterwards, and 23 about TNs). Our meta-analysis suggests a pooled prevalence for goiter before and after 1996 and for TNs of 22.8% (95% CI: 15.3%, 30.3%), 12.6% (95% CI: 9.4%, 15.8%) and 22.7% (95% CI: 18.3%, 27.0%), respectively. Egger's test of three independent categories revealed no evidence of publication bias (p = 0.101, 0.148 and 0.113, respectively).

CONCLUSIONS

The prevalence of goiter was reduced by almost half after 1996 in mainland China, so the USI program was considered beneficial. However, subgroup analysis suggests that both insufficient and excess iodine may be associated with goiter. The prevalence of goiter and TNs increased significantly after 2002, suggesting a risk of excessive iodine intake. Thus, salt iodization standardizations should be set according to local conditions.

Consequences of excess iodine

Iodine is a micronutrient that is essential for the production of thyroid hormones. The primary source of iodine is the diet via consumption of foods that have been fortified with iodine, including salt, dairy products and bread, or that are naturally abundant in the micronutrient, such as seafood. Recommended daily iodine intake is 150 µg in adults who are not pregnant or lactating. Ingestion of iodine or exposure above this threshold is generally well-tolerated. However, in certain susceptible individuals, including those with pre-existing thyroid disease, the elderly, fetuses and neonates, or patients with other risk factors, the risk of developing iodine-induced thyroid dysfunction might be increased. Hypothyroidism or hyperthyroidism as a result of supraphysiologic iodine exposure might be either subclinical or overt, and the source of the excess iodine might not be readily apparent.

The standard, intervention measures and health risk for high water iodine areas

Our study aims to clarify the population nutrient status in locations with different levels of iodine in the water in China; to choose effective measurements of water improvement(finding other drinking water source of iodine not excess) or non-iodised salt supply or combinations thereof; to classify the areas of elevated water iodine levels and the areas with endemic goiter; and to evaluate the risk factors of water iodine excess on pregnant women, lactating women and the overall population of women. From Henan, Hebei, Shandong and Shanxi province of China, for each of 50∼99 µg/L, 100∼149 µg/L, 150∼299 µg/L, and ≥300 µg/L water iodine level, three villages were selected respectively. Students of 6–12 years old and pregnant were sampled from villages of each water-iodine level of each province, excluded iodized salt consumer. Then the children's goiter volume, the children and pregnant's urinary iodine and water iodine were tested. In addition, blood samples were collected from pregnant women, lactating women and other women of reproductive age for each water iodine level in the Shanxi Province for thyroid function tests. These indicators should be matched for each person. When the water iodine exceeds 100 µg/L; the iodine nutrient of children are iodine excessive, and are adequate or more than adequate for the pregnant women. It is reasonable to define elevated water iodine areas as locations where the water iodine levels exceed 100 µg/L. The supply of non-iodised salt alone cannot ensure adequate iodine nutrition of the residents, and water improvement must be adopted, as well. Iodine excess increases the risk of certain thyroid diseases in women from one- to eightfold.

Goitre prevalence and epidemiological features in children living in areas with mildly excessive iodine in drinking-water

The prevalence of goitre in areas with mildly excessive iodine in drinking-water is still under debate. The aim of the present study was to explore the prevalence of goitre and its epidemiological characteristics in these areas using WHO criteria. To this end, three towns with a median water iodine (MWI) of 150-300 μg/l were selected randomly in Hengshui City of Hebei Province of China, and one town with a MWI of 105 μg/l was chosen as a control. A total of 452 children in the three towns and 120 children in the control town were randomly selected to measure thyroid volume (T vol) by ultrasound. The goitre status of these children was judged using the criteria recommended by the WHO. The overall goitre prevalences in the three towns were 24·6 % (111/452) by age-specific T vol and 33·0 % (149/452) by body surface area (BSA)-adjusted T vol, which were significantly higher than that in the control town by both age-specific T vol (14·0 % (17/120), P= 0·015) and BSA-adjusted T vol (17·5 % (21/120), P= 0·001). Significant differences were found neither in goitre prevalences across sex by both age-specific T vol (P= 0·078) and BSA-adjusted T vol (P= 0·692) nor in that across age group by both BSA-adjusted T vol (P= 0·461) and age-specific T vol (P= 0·183). The present study found a high prevalence of goitre in children living in areas with mildly excessive iodine in drinking-water in Hebei Province. No significant differences were found in goitre prevalences across sex and age group. These results suggest that the T vol reference values recommended by the WHO could be too low for Chinese children.

Iodine-induced thyroid dysfunction

PURPOSE OF REVIEW

To summarize the mechanisms of iodine-induced hypothyroidism and hyperthyroidism, identify the risk factors for thyroid dysfunction following an iodine load, and summarize the major sources of excess iodine exposure.

RECENT FINDINGS

Excess iodine is generally well tolerated, but individuals with underlying thyroid disease or other risk factors may be susceptible to iodine-induced thyroid dysfunction following acute or chronic exposure. Sources of increased iodine exposure include the global public health efforts of iodine supplementation, the escalating use of iodinated contrast radiologic studies, amiodarone administration in vulnerable patients, excess seaweed consumption, and various miscellaneous sources.

SUMMARY

Iodine-induced thyroid dysfunction may be subclinical or overt. Recognition of the association between iodine excess and iodine-induced hypothyroidism or hyperthyroidism is important in the differential diagnosis of patients who present without a known cause of thyroid dysfunction.

Role of iodine in thyroid physiology

Adequate levels of iodine, a trace element variably distributed on the earth, are required for the synthesis of the thyroid hormones thyroxine (T₄) and triiodothyronine (T₃). The iodide cycle consists of a series of transport, oxidation and coupling steps in thyroid follicular cells to produce thyroid hormone. The sodium/iodide symporter (NIS) transports iodide into the thyrocyte. Competitive inhibitors of NIS, such as perchlorate and thiocyanate, can decrease the entrance of iodide into the follicular cell. Pendrin is the primary protein that is responsible for iodide efflux out of the thyrocyte and into the follicular lumen. T₄ is deiodinated in target tissues to produce the active form of thyroid hormone, T₃, and other metabolites. Exposure to excessive iodine or chronic iodine deficiency may result in various clinical disorders. The Wolff-Chaikoff effect and Jöd-Basedow phenomenon describe mechanisms of thyroid autoregulation and dysregulation, respectively, during iodine excess. Population studies have determined that iodine deficiency exists in approximately 38% of the world's population, is the leading cause of preventable mental retardation, and is of particular concern to women and their infants. Finally, the unique role of iodine utilization in thyroid physiology has applications in many important clinical areas.

Endemic goitre and excessive iodine in urine and drinking water among Saharawi refugee children

Objective

To assess the prevalence of enlarged thyroid volume (Tvol) in Saharawi refugee children, and their urinary iodine concentration (UIC), and to identify possible sources of excess iodine intake.

Design

A cross-sectional survey was performed during January–February 2007. Tvol was measured by ultrasound and iodine concentration was analysed in casual urine samples, in household drinking water and in milk samples from household livestock.

Setting

The study was undertaken in four refugee camps in the Algerian desert.

Subjects

The subjects were 421 Saharawi children, 6–14 years old.

Results

Enlarged Tvol was found in 56 % (Tvol-for-age) and 86 % (Tvol-for-body-surface-area) of the children. The median (25th percentile–75th percentile, P25–P75) UIC was 565 (357–887) μg/l. The median (P25–P75) iodine concentration in household drinking water was 108 (77–297) μg/l. None of the children had UIC below 100 μg/l, 16 % had UIC between 100 and 299 μg/l, and 84 % had UIC above 300 μg/l. There was a positive association between Tvol and whether the household possessed livestock.

Conclusions

The children are suffering from endemic goitre and high UIC caused probably by an excessive intake of iodine. The excessive iodine intakes probably originate from drinking water and milk.

Tanzania national survey on iodine deficiency: impact after twelve years of salt iodation

BACKGROUND

In many low-income countries, children are at high risk of iodine deficiency disorders, including brain damage. In the early 1990s, Tanzania, a country that previously suffered from moderate to severe iodine deficiency, adopted universal salt iodation (USI) as an intervention strategy, but its impact remained unknown.

METHODS

We report on the first national survey in mainland Tanzania, conducted in 2004 to assess the extent to which iodated salt was used and its apparent impact on the total goitre prevalence (TGP) and urinary iodine concentrations (UIC) among the schoolchildren after USI was initiated. In 2004, a cross-sectional goitre survey was conducted; covering 140,758 schoolchildren aged 6 - 18 years were graded for goitre according to new WHO goitre classification system. Comparisons were made with district surveys conducted throughout most of the country during the 1980s and 90s. 131,941 salt samples from households were tested for iodine using rapid field test kits. UIC was determined spectrophotometrically using the ammonium persulfate digestion method in 4523 sub-sampled children.

RESULTS

83.6% (95% CI: 83.4 - 83.8) of salt samples tested positive for iodine. Whereas the TGP was about 25% on average in the earlier surveys, it was 6.9% (95%CI: 6.8-7.0) in 2004. The TGP for the younger children, 6-9 years old, was 4.2% (95%CI: 4.0-4.4), n = 41,965. In the 27 goitre-endemic districts, TGP decreased from 61% (1980s) to 12.3% (2004). The median UIC was 204 (95% CF: 192-215) microg/L. Only 25% of children had UIC <100 microg/L and 35% were > or = 300 microg/L, indicating low and excess iodine intake, respectively.

CONCLUSION

Our study demonstrates a marked improvement in iodine nutrition in Tanzania, twelve years after the initiation of salt iodation programme. The challenge in sustaining IDD elimination in Tanzania is now two-fold: to better reach the areas with low coverage of iodated salt, and to reduce iodine intake in areas where it is excessive. Particular attention is needed in improving quality control at production level and perhaps the national salt iodation regulations may need to be reviewed.

Effects of Kang-Jia-Wan, a Chinese medicinal herb officinal, on apoptosis induction in goiter of rats

ETHNOPHARMACOLOGICAL RELEVANCE

Kang-Jia-Wan (KJW), a traditional Chinese herbal medicine, is widely used to treat goiter in the clinics in China.

AIM

The mechanisms by which KJW treats goiter are unclear. It is known that insufficient apoptosis of thyrocytes is involved in the formation of goiter. Here, we investigated whether KJW could induce apoptosis in goiter of rats given methimazole (MMI).

MATERIALS AND METHODS

Fifty-six Wistar rats were randomly separated into four groups: normal, MMI, MMI+low-dose KJW and MMI+hig h-dose KJW. Except for the normal group (20 rats), all groups (each with 12 rats) were given 0.04% (w/v) MMI in their drinking water. One week later, the rats in MMI+low- and high-dose KJW groups were orally supplemented with KJW at 250 mg/kg d(-1) and 1000 mg/kg d(-1), respectively.

RESULTS

After KJW treatment for 12 weeks, the relative thyroid weight (mg/100g body weight) of the MMI+high-dose KJW group decreased significantly. Features of apoptosis were also apparent in thyroid tissues of rats given KJW treatment. Importantly, KJW markedly increased the caspase-3 and Fas protein expression, in a dose-dependent manner, in the thyroid specimens.

CONCLUSIONS

These results showed that KJW played a therapeutic role via apoptosis induction in the goitrous glands.

A iodúria de pacientes portadores de tireopatias autoimunes em Santo andré, SP, é comparável à dos indivíduos normais e estável nos últimos dez anos

OBJETIVO: Avaliar se o aumento de iodo na dieta seria o fator desencadeante de tireopatias autoimunes na cidade de Santo André, SP. MÉTODOS: Determinou-se a iodúria em amostra isolada de 58 pacientes, divididos em quatro grupos e de 13 indivíduos normais (controles). RESULTADOS: Iodúria: grupo 1 - hipertireoidismo = 203,5 ± 152,71 µg/L (média ± DP); grupo 2 hipotireoidismo = 258,31 ± 148,2 µg/L; grupo 3 - tireodite crônica autoimune = 244,29 ± 191,6 µg/L; grupo 4 - amiodarona = 1.157,5 ± 261,8 µg/L; grupo 5 - controles = 262,31 ± 146,2 µg/L. Comparadas as médias da iodúria entre os cinco grupos, dos grupos 1, 2, 3 e 5 não apresentaram diferenças significantes (p > 0,05) e todos diferiram do grupo 4 (p < 0,05). A iodúria dos grupos 1, 2, 3 e 5, obtida em 2002 e 2003, não diferiram dos valores determinados em 1994 em escolares em Santo André. CONCLUSÃO: Este estudo evidencia que o iodo não deve ser considerado o agente responsável pelas tireopatias autoimunes em Santo André, e outros fatores ambientais devem ser investigados.

Cigarette smoking and iodine as hypothyroxinemic stressors in U.S. women of childbearing age: a NHANES III analysis

BACKGROUND

Exposure to environmental thiocyanate through smoking has been suggested to lead to hypothyroxinemia, which potentially impairs brain development in the fetuses of affected women, though studies are conflicting. It was hypothesized that iodine status might modulate the effects of thiocyanate exposure on the prevalence of hypothyroxinemia in women of childbearing age.

DESIGN

The study population comprised 6967 women (age range: 15- 44 years) from the National Health and Nutrition Examination Survey (NHANES) III database. Smoking status was stratified into nonsmokers and those who smoked 1-10, 11-20, 21-30, and 31+ cigarettes a day. Iodine status was stratified based on urinary iodine excretion as <50, 50-99, 100-199, 200-299, and 300+ microug/L. Hypothyroxinemia was defined as the lower fifth percentile of total thyroxine levels among nonsmokers, adjusted for age and race/ethnicity. Univariate, multivariate, and regression analyses were conducted to evaluate the impact of smoking and urinary iodine excretion on the prevalence of hypothyroxinemia.

RESULTS

Increasing levels of cigarette smoking are associated with increasing prevalence of hypothyroxinemia [chi(2)(4) = 14.15, p = 0.007]. When analyzed by urinary iodine level, the hypothyroxinemic effect of smoking was limited to the highest two urinary iodine strata [chi(2)(4) = 41.48, p < 0.001; and chi(2)(4) = 40.62, p < 0.001]. A significant interaction effect between smoking and urinary iodine was noted, underscoring the relationship between high levels of urinary iodine excretion and smoking with respect to hypothyroxinemia.

CONCLUSIONS

Heavy smoking was associated with a higher prevalence of hypothyroxinemia. The impact of thiocyanate exposure from smoking on the prevalence of hypothyroxinemia is limited to those women of childbearing age with the highest urinary iodine excretion. Iodine supplementation should be cautiously considered in women of childbearing age who are smokers.

Thyroid autoimmunity in the current iodine environment

Iodine is essential for thyroid function. Thyroid disorders related to iodine deficiency decreased progressively with the continuous iodine prophylaxis and the increased iodine intake. An adverse effect resulting from iodine prophylaxis may be the induction of thyroid autoimmunity. Although experiments performed in animal models suggest that iodine could initiate or exacerbate thyroid autoimmunity, the role of iodine in humans remains controversial. Several observational studies in areas with adequate or high iodine intake suggest that there is an increase in the incidence of thyroid autoimmune disease. Moreover, intervention studies suggest that increased iodine intake may enhance thyroid autoimmunity too. However, not all studies generated the same findings, probably because of genetic, racial, and environmental differences. It seems that autoimmune exacerbation is a transient phenomenon. Studies have shown that in persons presenting thyroid antibodies, the levels of these antibodies progressively decrease when the majority of them react against a nonspecific pattern of thyroglobulin (Tg) epitopes. However, in a small number of these persons, the anti-Tg antibodies are similar to those in patients with patent thyroid autoimmune disease, reacting against specific immunodominant Tg epitopes, and their levels persist. One possible attractive explanation is that enhanced iodine intake increases the antigenicity of Tg through the incorporation of iodine into its molecule and the formation of iodinated Tg epitopes or even the generation of noniodinated pathogenetic Tg epitopes that are normally cryptic.

Incidence of iodine deficiency in patients presenting with goitre--discrepancy between clinical and ultrasonographic evaluation of the thyroid: comparison of patients with and without autoimmune thyroiditis--clinical, hormonal and urinary iodine excretion studies

In endemic areas iodine deficiency, and in iodine sufficient regions autoimmune thyroiditis, is the first aetiological factor for goitre. The aims of this study were to determine the incidence of iodine deficiency and autoimmune thyroiditis in patients presenting with goitre, to compare clinical and ultrasonographic assessment of thyroid size and to investigate the relationship between iodine and autoimmune thyroiditis. Patients diagnosed with goitre clinically (n = 204) were evaluated by their anthropometric measurements, ultrasonographic examination of the thyroid gland, thyroid function and TRH stimulation tests, thyroid autoantibodies and morning urinary iodine measurements. Thyroid volumes were evaluated according to three different reference criteria. Incidences of iodine deficiency and autoimmune thyroiditis were 54% and 17%. The incidences of iodine deficiency and excess were not significantly different in the autoimmune group (n = 35) compared to the non-autoimmune group (n = 169). In the autoimmune group, urinary iodine concentration correlated positively with serum thyroid hormones (FT3 r = 0.42, TT3 r = 0.38, TT4 r = 0.34) and negatively with serum TSH levels (r = 0.45). There were discrepancies between clinical and ultrasonographic evaluation of goitre, and between different reference criteria. This study revealed that iodine deficiency is still the first aetiological factor for goitre in our region and failed to show a relationship between iodine intake and autoimmune thyroid disease.

High thyroid volume in children with excess dietary iodine intakes

BACKGROUND

There are few data on the adverse effects of chronic exposure to high iodine intakes, particularly in children.

OBJECTIVE

The objective of the study was to ascertain whether high dietary intakes of iodine in children result in high thyroid volume (Tvol), a high risk of goiter, or both.

DESIGN

In an international sample of 6-12-y-old children (n = 3319) from 5 continents with iodine intakes ranging from adequate to excessive, Tvol was measured by ultrasound, and the urinary iodine (UI) concentration was measured. Regressions were done on Tvol and goiter including age, body surface area, sex, and UI concentration as covariates.

RESULTS

The median UI concentration ranged from 115 microg/L in central Switzerland to 728 microg/L in coastal Hokkaido, Japan. In the entire sample, 31% of children had UI concentrations >300 microg/L, and 11% had UI concentrations >500 microg/L; in coastal Hokkaido, 59% had UI concentrations >500 microg/L, and 39% had UI concentrations >1000 microg/L. In coastal Hokkaido, the mean age- and body surface area-adjusted Tvol was approximately 2-fold the mean Tvol from the other sites combined (P < 0.0001), and there was a positive correlation between log(UI concentration) and log(Tvol) (r = 0.24, P < 0.0001). In the combined sample, after adjustment for age, sex, and body surface area, log(Tvol) began to rise at a log(UI concentration) >2.7, which, when transformed back to the linear scale, corresponded to a UI concentration of approximately 500 microg/L.

CONCLUSIONS

Chronic iodine intakes approximately twice those recommended-indicated by UI concentrations in the range of 300-500 microg/L-do not increase Tvol in children. However, UI concentrations >/=500 microg/L are associated with increasing Tvol, which reflects the adverse effects of chronic iodine excess.

Changes in iodine excretion in 50-69-y-old denizens of an Arctic society in transition and iodine excretion as a biomarker of the frequency of consumption of traditional Inuit foods

BACKGROUND

Iodine intake in Greenland has been hypothesized to exceed 10 times the recommended amount. The transition from a traditional Arctic society may change the iodine intake, but no field studies have been performed.

OBJECTIVE

We aimed to ascertain iodine intakes, factors affecting iodine intake in circumpolar populations, and the usefulness of urinary iodine excretion as a biomarker for validation of Inuit food-frequency questionnaires.

DESIGN

Data were collected in a cohort study of 4 Greenland population groups: Inuit living in the capital city, the major town, and settlements in East Greenland and non-Inuit. Supplement use and lifestyle factors were evaluated with questionnaires, and dietary habits were ascertained with a food-frequency questionnaire. Iodine was measured in spot urine samples.

RESULTS

One percent of the population of Greenland was invited, and the participation rate was 95%. Less than 5% of Inuit but 55% of non-Inuit had urinary iodine excretion < 50 microg/24 h. Median urinary iodine excretion declined with the degree of decrease in the traditional lifestyle: it was 198, 195, 147, and 58 microg/24 h among Inuit in settlements, town, and city and in non-Inuit, respectively (P < 0.001). Participants were divided into diet groups calculated from Inuit food frequency. Iodine excretion decreased with increasing intake of imported foods (P < 0.001). In regression models, type of diet and the subject's lifestyle, sex, weight, ethnicity, and intake of iodine-containing supplements affected urinary iodine excretion.

CONCLUSIONS

Circumpolar non-Inuit are at risk of iodine deficiency. Departure from the traditional Inuit diet lowers iodine intake, which should be monitored in Arctic societies. Urinary iodine excretion may be a useful biomarker of traditional Inuit food frequency.

Moléstias associadas à carência crônica de iodo

Fundamentalmente, a glândula tiróide, face à carência de iodo, se adapta por incremento da captação deste halogênio, aumenta a sua massa glandular (bócio), induz secreção preferencial de T3 e eleva a síntese e liberação de TSH. Os exames laboratoriais e de imagem permitem a comprovação dos mecanismos adaptativos. A iodúria permite avaliação quantitativa do grau de carência iódica. Em algumas populações, coexiste a influência de bocígenos naturais presentes nos alimentos consumidos localmente. O cretinismo endêmico é síndrome neurológica e endócrina que conduz o indivíduo a quadro severo de rebaixamento mental e surdo-mudez. No Brasil, as moléstias associadas à carência de iodo foram sempre avaliadas por inquéritos nacionais em escolares. A correção da deficiência de iodo se faz pela adição de iodato de potássio ao sal de consumo humano. Várias leis e decretos foram elaborados tentando aperfeiçoar o sistema universal de iodação do sal, que, mais recentemente, foi aprimorado e tornou-se mais eficiente em propiciar iodo a toda população brasileira.