Excessive Iodine Intake Research Articles

Iodine status five years after the mandatory salt iodization legislation indicates above requirement: a cross sectional study in Northwest Ethiopia

BackgroundIodine deficiency is one of a major nutritional problem. The study aimed to assess the iodine status of populations in Dabat district using median urinary iodine concentration (UIC) in school-age children (6–12 years) and compared the results with goiter prevalence.MethodsThe study used a cross-sectional study design. The study was conducted in Dabat district, northwest Ethiopia in May 2016. Spot urine samples were used for the determination of UIC. Manual examination of the thyroid gland was performed to assess presence of goiter. The MBI international Rapid Test Kits (RTK) were used to determine the level of salt iodine content. Children aged 6–12 years were recruited from schools using a multistage stratified sampling. One-way Analysis of Variance (ANOVA) was used to compare mean of log-transformed UIC values among key variables. Significant was determined at P-value less than 0.05.ResultsA total of 358 school age children enrolled to the study. The mean age of children was 10.8((Standard Deviation (SD) = 1.45) years and 56.7% were males. The median UIC was 235 μg/l ((Inter Quartile Range (IQR): 161, 320]. Excessive iodine intake and inadequate iodine intake was observed on 29.1 and 8.7% of school aged children, respectfully. The coverage of iodized salt use in school-age children were 66.8%. The UIC was higher in urban children than rural counterparts and in those used adequately iodised salt than inadequately iodized salt (P < 0.05). Thirty-four percent of school-age children had a goiter. The prevalence of grade 1 and grade 2 goiter was 26.5 and 7.5%, respectively. There was a poor agreement between UIC and goiter (k = 0.1) in classifying iodine status of populations.ConclusionsThe study population is classified as above requirements by median UIC in school-age children but severe iodine deficiency by goiter prevalence. Further research investigating the agreement between UIC and goiter prevalence in classifying iodine status of populations with various iodine status is warranted.

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.

The catalytic role of iodine excess in loss of homeostasis in autoimmune thyroiditis.

To review the latest developments concerning the role of iodine in the pathophysiology of autoimmune thyroiditis. Recent studies have provided evidence that in areas with excess iodine intake, increased incidence of autoimmune thyroiditis marked by high titers of thyroid peroxidase and thyroglobulin antibodies has occurred. Investigations in the NOD.H2h4 mouse, a strain prone to AIT, showed that they are better adapted to the Wolff-Chaikoff effect. To provide an overview of the studies conducted during the last few years implicating iodine in the development and manifestation of autoimmune thyroiditis.

Multiple nutritional factors and thyroid disease, with particular reference to autoimmune thyroid disease.

Hashimoto's thyroiditis (HT) and Graves' disease (GD) are examples of autoimmune thyroid disease (AITD), the commonest autoimmune condition. Antibodies to thyroid peroxidase (TPO), the enzyme that catalyses thyroid-hormone production and antibodies to the receptor for the thyroid-stimulating hormone, are characteristic of HT and GD, respectively. It is presently accepted that genetic susceptibility, environmental factors, including nutritional factors and immune disorders contribute to the development of AITD. Aiming to investigate the effect of iodine, iron and selenium in the risk, pathogenesis and treatment of thyroid disease, PubMed and the Cochrane Library were searched for relevant publications to provide a narrative review. Iodine: chronic exposure to excess iodine intake induces autoimmune thyroiditis, partly because highly-iodinated thyroglobulin (Tg) is more immunogenic. The recent introduction of universal salt iodisation can have a similar, although transient, effect. Iron: iron deficiency impairs thyroid metabolism. TPO is a haem enzyme that becomes active only after binding haem. AITD patients are frequently iron-deficient since autoimmune gastritis, which reduces iron absorption and coeliac disease which causes iron loss, are frequent co-morbidities. In two-thirds of women with persistent symptoms of hypothyroidism despite appropriate levothyroxine therapy, restoration of serum ferritin above 100 µg/l ameliorated symptoms. Selenium: selenoproteins are essential to thyroid action. In particular, the glutathione peroxidases remove excessive hydrogen peroxide produced there for the iodination of Tg to form thyroid hormones. There is evidence from observational studies and randomised controlled trials that selenium, probably as selenoproteins, can reduce TPO-antibody concentration, hypothyroidism and postpartum thyroiditis. Appropriate status of iodine, iron and selenium is crucial to thyroid health.

Reply to “Adverse effects on thyroid of Chinese children exposed to long-term iodine excess: optimal and safe Tolerable Upper Intake Levels of iodine for 7- to 14-y-old children”

Background The adverse effects of iodine excess on the thyroid in children are not well understood, and the Tolerable Upper Intake Level for iodine in children is unclear. Objective The aims of this study were to assess the effects of chronic long-term iodine excess on thyroid function in children and to explore the safe Tolerable Upper Intake Level of iodine in Chinese children. Design A multistage cross-sectional study was conducted in 2224 children from areas with adequate to excessive iodine content in drinking water. Repeated samples of 24-h urine and spot urine samples were collected to estimate habitual daily iodine intakes of children. The thyroid volume in children was measured and blood samples were collected to determine thyroid function. Results The habitual iodine intake of children was 298 μg/d (range: 186-437 μg/d). The total goiter rate was 9.7%, 232 (11.2%) children had hyperthyrotropinemia, and 232 (11.2%) children had thyroglobulin (Tg) concentrations >40 μg/L. The prevalence of hyperthyrotropinemia was >10% in children at iodine intakes of 200-300 μg/d. Tg concentrations increased with increased iodine intake (β = 0.5; 95% CI: 0.4, 0.6), and the prevalence of Tg >40 μg/L was >3% in all iodine-intake groups. Multivariate logistic regression analysis indicated that the risk of total goiter significantly increased at iodine intakes ≥250-299 μg/d in 7- to 10-y-old children (OR: 8.8; 95% CI: 2.3, 34.0) and at iodine intakes ≥300-399 μg/d in 11- to 14-y-old children (OR: 5.2; 95% CI: 1.5, 18.3). However, there were no consistent differences in the risk of hyperthyrotropinemia and Tg >40 μg/L in children between different iodine-intake groups. Conclusions Thyroid volume and goiter appear to be more sensitive indicators of thyroid stress than thyrotropin and Tg in children with long-term excess iodine intakes. We recommend 250 and 300 μg/d as safe Tolerable Upper Intake Levels of iodine for children aged 7-10 y and 11-14 y, respectively. This trial was registered at www.clinicaltrials.gov as NCT02915536.

Urinary iodine concentration: a biochemical parameter for assessing the iodine status

Iodine is a micronutrient, which is essential for the synthesis of thyroid hormones. Thyroid hormones play a major role in the development of different functional components in different stages of life. The relationship between iodine intake level of a population and occurrences of thyroid disorders U-shaped with an increase from both low and high iodine intake. Iodine deficiency disorders (IDDs) are a major health problem worldwide in all age groups, but infants, school children, and pregnant and lactating women are vulnerable. During pregnancy and lactation, the fetus and infants are sensitive to maternal iodine intake. Even mild iodine deficiency may lead to irreversible brain damage during this period. A main cause of IDDs of neonates and infants is maternal iodine deficiency. Universal salt iodization strategy has been initiated by the World Health Organization and United Nation International Children Emergency Fund by the year 1993 for correction and prevention of iodine deficiency. Excessive iodine causes hypothyroidism, iodine-induced hyperthyroidism and autoimmune thyroid diseases. Iodine deficiency and excessive iodine, both cause goiter. There are many indicators for assessing the IDDs, such as measurement of thyroid size by palpation or ultrasonography, serum thyroid stimulating hormone, and thyroglobulin but these are less sensitive, costly and sometimes interpretation is difficult. Urinary iodine concentration (UIC) is a well-accepted, cost-efficient, and easily obtainable indicator of iodine status. Since the majority of iodine absorbed by the body is excreted in the urine, it is considered a sensitive marker of current iodine intake and can reflect recent changes in iodine status. Iodine requirements are greatly increased during pregnancy and lactation, owing to metabolic changes. During intrauterine life, maternal iodine is the only source of iodine for a fetus. UIC determines the iodine status of pregnant and lactating women. Breast milk is the only source of iodine for exclusively breastfed neonates and infants. Breast milk iodine concentration can be determined by UIC. UIC predicts the adverse health consequences of excessive iodine intake such as goiter, hypothyroidism, and hyperthyroidism. This review presents that iodine status in different groups of a population can be determined by UIC which will be helpful in assessing the iodine status in a community, finding out the cause of thyroid disorders, to predict the risk of adverse health effects of iodine deficiency and excessive iodine, and in making plan for iodine supplementation.Mediscope Vol. 5, No. 2: Jul 2018, Page 30-35

Guidance on the monitoring of salt iodization programmes and determination of population iodine status: Russian language version

Over the last two decades, there has been remarkable progress towards eliminating iodine deficiency (ID). While there has been remarkable success, there have been several notable changes in the way that salt iodization programs have been designed and monitored, as well as the general landscape in which salt iodization is being implemented. This article is based on the “Guidance on the monitoring of salt iodization programmes and determination of population iodine status”. It summarizes important lessons learned on how to better track the performance of and refine salt iodization programs. The adequacy of iodine intakes should be examined among different subsets of the population (not only school-aged children), especially among groups vulnerable to deficiency (such as pregnant women). The acceptable range of ‘adequate’ iodine intake among school-age children can be widened from 100–199 µg/L to 100–299 µg/L eliminating the range of 200–299 µg/L that previously indicates ‘more than adequate’ iodine intake. The interpretation of mUIC of ≥ 300 µg/L as ‘excessive iodine intake’ remains unchanged. With currently available methods, the mUIC can only be used to define population iodine status and not to quantify the proportion of the population with iodine deficiency or iodine excess. National salt iodization programmes should monitor the use of iodized salt in processed foods. If the salt contained in such foods is well iodized, it can be an important source of iodine and may help explain iodine sufficiency in settings where household iodized salt coverage is low.

Рекомендации по мониторингу программ йодирования соли и оценке статуса йодной обеспеченности населения (русскоязычная версия)

Over the last two decades, there has been remarkable progress towards eliminating iodine deficiency (ID). While there has been remarkable success, there have been several notable changes in the way that salt iodization programs have been designed and monitored, as well as the general landscape in which salt iodization is being implemented. This article is based on the “Guidance on the monitoring of salt iodization programmes and determination of population iodine status”. It summarizes important lessons learned on how to better track the performance of and refine salt iodization programs. The adequacy of iodine intakes should be examined among different subsets of the population (not only school-aged children), especially among groups vulnerable to deficiency (such as pregnant women). The acceptable range of ‘adequate’ iodine intake among school-age children can be widened from 100–199 µg/L to 100–299 µg/L eliminating the range of 200–299 µg/L that previously indicates ‘more than adequate’ iodine intake. The interpretation of mUIC of ≥ 300 µg/L as ‘excessive iodine intake’ remains unchanged. With currently available methods, the mUIC can only be used to define population iodine status and not to quantify the proportion of the population with iodine deficiency or iodine excess. National salt iodization programmes should monitor the use of iodized salt in processed foods. If the salt contained in such foods is well iodized, it can be an important source of iodine and may help explain iodine sufficiency in settings where household iodized salt coverage is low.

Guidance on the monitoring of salt iodization programmes and determination of population iodine status: Russian language version

Over the last two decades, there has been remarkable progress towards eliminating iodine deficiency (ID). While there has been remarkable success, there have been several notable changes in the way that salt iodization programs have been designed and monitored, as well as the general landscape in which salt iodization is being implemented. This article is based on the “Guidance on the monitoring of salt iodization programmes and determination of population iodine status”. It summarizes important lessons learned on how to better track the performance of and refine salt iodization programs. The adequacy of iodine intakes should be examined among different subsets of the population (not only school-aged children), especially among groups vulnerable to deficiency (such as pregnant women). The acceptable range of ‘adequate’ iodine intake among school-age children can be widened from 100–199 µg/L to 100–299 µg/L eliminating the range of 200–299 µg/L that previously indicates ‘more than adequate’ iodine intake. The interpretation of mUIC of ≥ 300 µg/L as ‘excessive iodine intake’ remains unchanged. With currently available methods, the mUIC can only be used to define population iodine status and not to quantify the proportion of the population with iodine deficiency or iodine excess. National salt iodization programmes should monitor the use of iodized salt in processed foods. If the salt contained in such foods is well iodized, it can be an important source of iodine and may help explain iodine sufficiency in settings where household iodized salt coverage is low.

Effect of Excess Iodine Intake from Iodized Salt and/or Groundwater Iodine on Thyroid Function in Nonpregnant and Pregnant Women, Infants, and Children: A Multicenter Study in East Africa.

Acute excess iodine intake can damage the thyroid, but the effects of chronic excess iodine intake are uncertain. Few data exist for pregnant and lactating women and infants exposed to excessive iodine intake. This was a multicenter cross-sectional study. At study sites in rural Kenya and urban Tanzania previously reporting iodine excess in children, urinary iodine concentration (UIC), thyrotropin, total thyroxine, and thyroglobulin (Tg) were measured in school-age children (SAC), women of reproductive age, pregnant (PW) and lactating women, and breast-feeding and weaning infants. In a national study in Djibouti, UIC was measured in SAC and PW. At all sites, daily iodine intake was estimated based on UIC, and iodine concentration was measured in household salt and drinking water. The total sample size was 4636: 1390, 2048, and 1198 subjects from Kenya, Tanzania, and Djibouti, respectively. In Kenya and Tanzania: (i) median UIC was well above thresholds for adequate iodine nutrition in all groups and exceeded the threshold for excess iodine intake in SAC; (ii) iodine concentrations >40 mg of iodine/kg were found in approximately 55% of household salt samples; (iii) iodine concentrations ≥10 μg/L were detected in 9% of drinking water samples; (iv) Tg was elevated in all population groups, but the prevalence of thyroid disorders was negligible, except that 5-12% of women of reproductive age had subclinical hyperthyroidism and 10-15% of PW were hypothyroxinemic. In Djibouti: (i) the median UIC was 335 μg/L (interquartile range [IQR] = 216-493 μg/L) in SAC and 265 μg/L (IQR = 168-449 μg/L) in PW; (ii) only 1.6% of Djibouti salt samples (n = 1200) were adequately iodized (>15 mg/kg); (iii) the median iodine concentration in drinking water was 92 μg/L (IQR = 37-158 μg/L; n = 77). In all countries, UIC was not significantly correlated with salt or water iodine concentrations. Although iodine intake was excessive and Tg concentrations were elevated, there was little impact on thyroid function. Chronic excess iodine intake thus appears to be well tolerated by women, infants, and children. However, such high iodine intake is unnecessary and should be avoided. Careful evaluation of contributions from both iodized salt and groundwater iodine is recommended before any review of iodization policy is considered.

Current state of iodine nutrition in Filipino school-aged children.

Globally, although progress in eliminating iodine deficiency disorders (IDD) has been reported, IDD is still considered to be a global health problem. As school-aged children are the most accessible population group, their urinary iodine (UI) concentration data are accepted and used as an indicator of IDD for the general population. The aim of this study was to reassess the national, regional, and provincial estimates of UI as a measure of IDD among Filipino school-aged children. Casual urine samples were collected from 22 588 children, 6 to 12 y of age, from participating households in the eighth National Nutrition Survey. UI was determined based on the catalytic action of iodine in the Sandell-Kolthoff reaction and IDD was evaluated using criteria from the World Health Organization, United Nations Children's Fund, International Council for Control of Iodine Deficiency Disorders criteria. The median UI level among Filipino school-aged children was 168 μg/L, corresponding to optimal iodine nutrition; whereas 23.2% had UI reflective of excessive iodine intake. Cjildren in the Zamboanga Peninsula Region had median UI level of 68 μg/L and 41.1% of participants had UI values <50 μg/L, which is indicative of mild iodine deficiency. Children from Guimaras and Zamboanga del Norte, or 2.4% of the provinces, had moderate iodine deficiency. Although the median UI level of school-age children was optimal, there are pockets of inadequacy and excessive intake that need special concern for targeted intervention.

Thyroid dysfunction in region of excess iodine intake of eastern Nepal

Iodine deficiency is one of most common micronutrient deficiencies worldwide, the consequences of excess iodine should not be ignored. Both chronic iodine excess and iodine deficiency can result in thyroid dysfunction in populations, especially children and pregnant women if not corrected. This is because children and pregnant women are very vulnerable to iodine deficiency and sensitive to iodine changes

Urinary Iodine Concentration and Mortality Among U.S. Adults.

Iodine deficiency has long been recognized as an important public health problem. Global approaches such as salt iodization that aim to overcome iodine deficiency have been successful. Meanwhile, they have led to excessive iodine consumption in some populations, thereby increasing the risks of iodine-induced thyroid dysfunction, as well as the comorbidities and mortality associated with hypothyroidism and hyperthyroidism. This study aimed to elucidate whether iodine intake is associated with mortality among U.S. adults. This was an observational study to estimate mortality risks according to urinary iodine concentration (UIC) utilizing a nationally representative sample of 12,264 adults aged 20-80 years enrolled in the National Health and Nutrition Examination Survey (NHANES) III. Crude and multivariable Cox proportional hazards regression models were employed to investigate the association between UIC (<50, 50-99, 100-299, 300-399, and ≥400 μg/L) and mortalities (all-cause, cardiovascular, and cancer). In sensitivity analyses, the study adjusted for total sodium intake and fat/calorie ratio in addition to other potential confounders. Stratum-specific analyses were also conducted to estimate the effects of UIC on mortality according to age, sex, race/ethnicity, and estimated glomerular filtration rate category. Over a median follow-up of 19.2 years, there were 3159 deaths from all causes. Participants with excess iodine exposure (UIC ≥400 μg/L) were at higher risk for all-cause mortality compared to those with adequate iodine nutrition (hazard ratio = 1.19 [confidence interval 1.04-1.37]). Elevated hazard ratios of cardiovascular and cancer mortality were also found, but the confidence interval of the effect estimates included the null value for both outcomes. Low UIC was not associated with increased mortality. Restricted cubic spline models showed similar results for all outcomes. The results did not change substantially after adjusting for total sodium intake and fat/calorie ratio. None of the potential interactions were statistically significant on a multiplicative scale. Higher all-cause mortality among those with excess iodine intake compared to individuals with adequate iodine intake highlights the importance of monitoring population iodine status. Further studies with longitudinal measures of iodine status are needed to validate these results and to assess the potential risks excess iodine intake may have on long-term health outcomes.

Smoking Is Positively Associated with Antithyroperoxidase Antibodies and Antithyroglobulin Antibodies in Populations with Mildly Deficient Iodine Intake.

To evaluate the relationship between smoking and both antithyroperoxidase antibody (TPOAb) and antithyroglobulin antibody (TgAb) positivity in subjects from Panshan, Zhangwu, and Huanghua with mildly deficient, more than adequate, and excessive iodine intake, respectively. Smoking-related data were collected by questionnaire, and laboratory measurements of TPOAb, TgAb, and thyrotropin (TSH) were determined at baseline and follow-up. (1) A 1.48-fold increased risk of TPOAb positivity was found in smokers than in non-smokers after adjusting for confounders (age, sex, and areas) (OR[95% CI] = 1.48[1.12-1.95], p = 0.01). (2) Among female subjects, the prevalence of thyroid autoantibodies in smokers was increased than that in non-smokers in Panshan, Zhangwu, and Huanghua (TPOAb): 16.79 vs. 8.89%, 14.14 vs. 11.09%, 19.53 vs. 9.57%; TgAb 15.32 vs. 9.29%, 12.79 vs. 11.94%, 17.19 vs. 10.55%, respectively). The difference was significant in Panshan after adjusting for age. (3) Female long-term smokers (> 20years) had an increased frequency of thyroid autoantibody positivity than non-smokers after adjusting for confounders (TPOAb OR[95% CI] = 1.60[1.10-2.34]; TgAb OR[95% CI] = 1.31[0.88-1.94]). (4) There was no difference in the incidence of thyroid autoantibodies among non-smokers, new smokers, and long-term smokers at follow-up. (5) TSH was greater in TPOAb-positive subjects than in seronegative smokers (1.56 vs. 1.20mU/L, p < 0.001) and non-smokers (1.97 vs. 1.58mU/L, p < 0.001). However, TSH was also greater in non-smokers than in smokers, regardless of whether subjects were positive (1.97 vs. 1.56mU/L, p = 0.04) or negative (1.58 vs. 1.20mU/L, p < 0.001) for TPOAb. Long-term smoking could increase the prevalence of thyroid autoantibodies in a population with mildly deficient iodine intake. TSH levels were lesser in smokers than in non-smokers and greater in subjects with thyroid autoantibody positivity than in seronegative subjects. The influence of smoking on TSH levels was independent of thyroid autoantibody levels.

Excessive Iodine Intake and Subclinical Hypothyroidism in Children and Adolescents Aged 6-19 Years: Results of the Sixth Korean National Health and Nutrition Examination Survey, 2013-2015.

Iodine is an important element for the synthesis of thyroid hormone, and its deficiency or excessive intake is associated with various thyroid diseases. Little is known about the association between iodine status and thyroid function among children and adolescents living in iodine-rich areas. Therefore, this study analyzed this association using data from a nationwide survey. From the Korea National Health and Nutrition Examination Surveys VI (2013-2015) data, 1288 subjects (711 male) aged 6-19 years who underwent a urinary iodine concentration (UIC) test and 1000 subjects (564 male) aged 10-19 years who underwent a thyroid function test were included in this study. Serum levels of thyrotropin (TSH), free thyroxine (fT4), and thyroperoxidase antibodies (TPOAb) were analyzed. Subclinical hypothyroidism (SCH) was defined as TSH >5.5 μIU/mL with a normal fT4 level. Median daily iodine intake was calculated from the UIC. Daily sodium intake was derived from the nutritional survey data of 1181 subjects. The median UIC was 449 μg/L (range 15-21,905 μg/L), and the prevalence rates of UIC ≥300 μg/L and ≥1000 μg/L were 64.9% and 25.0%, respectively. The prevalence rates of a sodium intake >2000 mg/day and iodine intake >2400 μg/day were 75.0% (885/1181) and 12.7% (164/1288), respectively. The prevalence rates of SCH and TPOAb >34 IU/mL were 7.2% (72/1000) and 2.3% (23/1000), respectively. The prevalence of SCH was significantly higher in the iodine deficient and iodine excess groups compared to those in the UIC 100-299.9 μg/L group (p = 0.038). Therefore, there was a U-shaped and inverted U-shaped correlation between serum levels of TSH and fT4 with UIC, respectively. These correlations were especially prominent when UIC was >1000 μg/L. There was no definite correlation between TPOAb and UIC. Excess iodine was prevalent in Korean children and adolescents, and it may be associated with SCH. Therefore, monitoring the iodine status and education on adequate intake are needed in iodine-rich areas.

Prevalence of thyroid function in pregnant and lactating women in areas with different iodine levels of Shanxi province

Objective: To investigate the effects of high iodine intake on thyroid function in pregnant and lactating women. Methods: A cross sectional epidemiological study was conducted among 130 pregnant women and 220 lactating women aged 19-40 years in areas with high environment iodine level (>300 μg/L) or proper environment iodine level (50-100 μg/L) in Shanxi in 2014. The general information, urine samples and blood samples of the women surveyed and water samples were collected. The water and urine iodine levels were detected with arsenic and cerium catalysis spectrophotometric method, the blood TSH level was detected with electrochemiluminescence immunoassay, and thyroid stimulating hormone (FT(4)), antithyroid peroxidase autoantibody (TPOAb) and anti-thyroglobulin antibodies (TGAb) were detected with chemiluminescence immunoassay. Results: The median urine iodine levels of the four groups were 221.9, 282.5, 814.1 and 818.6 μg/L, respectively. The median serum FT(4) of lactating women in high iodine area and proper iodine area were 12.96 and 13.22 pmol/L, and the median serum TSH was 2.45 and 2.17 mIU/L, respectively. The median serum FT(4) of pregnant women in high iodine area and proper iodine area were 14.66 and 16.16 pmol/L, and the median serum TSH was 2.13 and 1.82 mIU/L, respectively. The serum FT(4) levels were lower and the abnormal rates of serum TSH were higher in lactating women than in pregnant women in both high iodine area and proper iodine area, the difference was statistically significant (FT(4): Z=-6.677, -4.041, P<0.01; TSH: Z=8.797, 8.910, P<0.01). In high iodine area, the abnormal rate of serum FT(4) in lactating women was higher than that in pregnant women, the difference was statistically significant (Z=7.338, P=0.007). The serum FT(4) level of lactating women in high iodine area was lower than that in proper iodine area, the difference was statistically significant (Z=-4.687, P=0.000). In high iodine area, the median serum FT(4) in early pregnancy, mid-pregnancy and late pregnancy was 16.26, 14.22 and 14.80 pmol/L, respectively, and the median serum TSH was 1.74, 1.91 and 2.38 mIU/L, respectively. In high iodine area, the serum FT(4) level in early pregnancy was higher than that in mid-pregnancy and late pregnancy, and the serum TSH level was lower than that in mid-pregnancy and late pregnancy, the difference was statistically significant (FT(4): Z=-2.174, -2.238, P<0.05; TSH: Z=-2.985, -1.978, P<0.05). There were no significant differences in the positive rates of serum thyroid autoantibodies among the four groups of women and women in different periods of pregnancy (P>0.05). The morbidity rates of subclinical hyperthyroidism in pregnant women and lactating women in high iodine area were obviously higher than those in proper iodine areas, the difference was statistically significant (χ(2)=5.363, 5.007, P<0.05). Conclusions: Excessive iodine intake might increase the risk of subclinical hypothyroidism in pregnant women and lactating women. It is suggested to strengthen the iodine nutrition and thyroid function monitoring in women, pregnant women and lactating women in areas with high environmental iodine.

Adverse effects on thyroid of Chinese children exposed to long-term iodine excess: optimal and safe Tolerable Upper Intake Levels of iodine for 7- to 14-y-old children

The adverse effects of iodine excess on the thyroid in children are not well understood, and the Tolerable Upper Intake Level for iodine in children is unclear. The aims of this study were to assess the effects of chronic long-term iodine excess on thyroid function in children and to explore the safe Tolerable Upper Intake Level of iodine in Chinese children. A multistage cross-sectional study was conducted in 2224 children from areas with adequate to excessive iodine content in drinking water. Repeated samples of 24-h urine and spot urine samples were collected to estimate habitual daily iodine intakes of children. The thyroid volume in children was measured and blood samples were collected to determine thyroid function. The habitual iodine intake of children was 298μg/d (range: 186-437μg/d). The total goiter rate was 9.7%, 232 (11.2%) children had hyperthyrotropinemia, and 232 (11.2%) children had thyroglobulin (Tg) concentrations >40μg/L. The prevalence of hyperthyrotropinemia was >10% in children at iodine intakes of 200-300μg/d. Tg concentrations increased with increased iodine intake (β=0.5; 95% CI: 0.4, 0.6), and the prevalence of Tg >40μg/L was >3% in all iodine-intake groups. Multivariate logistic regression analysis indicated that the risk of total goiter significantly increased at iodine intakes ≥250-299μg/d in 7- to 10-y-old children (OR: 8.8; 95% CI: 2.3, 34.0) and at iodine intakes ≥300-399μg/d in 11- to 14-y-old children (OR: 5.2; 95% CI: 1.5, 18.3). However, there were no consistent differences in the risk of hyperthyrotropinemia and Tg >40μg/L in children between different iodine-intake groups. Thyroid volume and goiter appear to be more sensitive indicators of thyroid stress than thyrotropin and Tg in children with long-term excess iodine intakes. We recommend 250 and 300μg/d as safe Tolerable Upper Intake Levels of iodine for children aged 7-10 y and 11-14 y, respectively. This trial was registered at www.clinicaltrials.gov as NCT02915536.

Thyroid dysfunction in region of excess iodine intake of Eastern Nepal

&lt;p class="abstract"&gt;&lt;strong&gt;Background:&lt;/strong&gt; Iodine deficiency as well as iodine excess can result in an increased prevalence of thyroid disorders. The prevalence of excess iodine nutrition is increasing all over the world. The aim of the present study was to find the occurrence of iodine nutrition status in primary school children of Eastern Nepal and find the prevalence of associated thyroid dysfunction among those with excess urinary iodine concentration.&lt;/p&gt;&lt;p class="abstract"&gt;&lt;strong&gt;Methods:&lt;/strong&gt; A community based cross sectional study was conducted in Udayapur district which is located in Eastern part of Nepal. Primary school aged children (6 years to 12 years) were enrolled in this study from three schools. Blood and urine samples were collected and assayed for urinary iodine concentration (UIC), free thyroid hormones (fT&lt;sub&gt;3&lt;/sub&gt; and fT&lt;sub&gt;4&lt;/sub&gt;), and thyroid stimulating hormone (TSH). &lt;/p&gt;&lt;p class="abstract"&gt;&lt;strong&gt;Results:&lt;/strong&gt; The median UIC was 232.27 µg/L. The iodine status showed that 15.5% (n=31) had low UIC, 21% (n=42) had above requirement and 36% (n=72) had excessive iodine nutrition status. The mean concentration of fT&lt;sub&gt;3&lt;/sub&gt; and fT&lt;sub&gt;4&lt;/sub&gt; was 2.87 pg/ml and 1.21 ng/dl respectively, while the median TSH concentration was 3.03 mIU/L. The prevalence of thyroid dysfunction was 10% (n=20) with subclinical hypothyroidism being the most common. Majority of participants with subclinical hypothyroidism had excess UIC.&lt;/p&gt;&lt;p class="abstract"&gt;&lt;strong&gt;Conclusions:&lt;/strong&gt; Above requirement and excess iodine nutrition is more common in region where there is unregulated consumption and improper monitoring of iodized salt. Subclinical hypothyroidism is common in regions of excess iodine nutrition.&lt;/p&gt;

Universal Salt Iodization Provides Sufficient Dietary Iodine to Achieve Adequate Iodine Nutrition during the First 1000 Days: A Cross-Sectional Multicenter Study

BackgroundDietary iodine requirements are high during pregnancy, lactation, and infancy, making women and infants vulnerable to iodine deficiency. Universal salt iodization (USI) has been remarkably successful for preventing iodine deficiency in the general population, but it is uncertain if USI provides adequate iodine intakes during the first 1000 d. ObjectiveWe set out to assess if USI provides sufficient dietary iodine to meet the iodine requirements and achieve adequate iodine nutrition in all vulnerable population groups. MethodsWe conducted an international, cross-sectional, multicenter study in 3 study sites with mandatory USI legislation. We enrolled 5860 participants from 6 population groups (school-age children, nonpregnant nonlactating women of reproductive age, pregnant women, lactating women, 0–6-mo-old infants, and 7–24-mo-old infants) and assessed iodine status [urinary iodine concentration (UIC)] and thyroid function in Linfen, China (n = 2408), Tuguegarao, the Philippines (n = 2512), and Zagreb, Croatia (n = 940). We analyzed the iodine concentration in household salt, breast milk, drinking water, and cow's milk. ResultsThe salt iodine concentration was low (<15 mg/kg) in 2.7%, 33.6%, and 3.1%, adequate (15–40 mg/kg) in 96.3%, 48.4%, and 96.4%, and high (>40 mg/kg) in 1.0%, 18.0%, and 0.5% of household salt samples in Linfen (n = 402), Tuguegarao (n = 1003), and Zagreb (n = 195), respectively. The median UIC showed adequate iodine nutrition in all population groups, except for excessive iodine intake in school-age children in the Philippines and borderline low intake in pregnant women in Croatia. ConclusionSalt iodization at ∼25 mg/kg that covers a high proportion of the total amount of salt consumed supplies sufficient dietary iodine to ensure adequate iodine nutrition in all population groups, although intakes may be borderline low during pregnancy. Large variations in salt iodine concentrations increase the risk for both low and high iodine intakes. Strict monitoring of the national salt iodization program is therefore essential for optimal iodine nutrition. This trial was registered at clinicaltrials.gov as NCT02196337.

Associations of urinary iodine and blood selenium levels with subclinical hypothyroidism and thyroid antibodies during the first half pregnancy in Tianjin women

Objective To investigate the associations of urinary iodine concentration(UIC)and blood selenium levels with subclinical hypothyroidism and thyroid antibodies during the first half pregnancy in women. Methods A total of 239 pregnant women(7-20 weeks)were selected. The baseline data were collected, and serum TSH, FT4, thyroid peroxidase antibody(TPOAb), thyroglobulin antibody(TgAb), blood selenium, and urinary iodine concentration(UIC)levels were measured. Results The median level of urinary iodine among 239 women was 156.96 μg/L. The distributions of pregnant women with iodine deficiency, iodine adequate, more-than-adequate or excessive iodine intake were 43.9%, 38.9%, 17.2%, respectively. The percentage of more-than-adequate and excessive iodine in women with subclinical hypothyroidism was higher than that in women with euthyroidism. The serum TSH level in women with UIC≥250 μg/L was higher than those with 150≤UIC<250 μg/L and UIC<150 μg/L(P<0.05). The serum TSH level in women with blood selenium<95 μg/L was higher than those with selenium≥95 μg/L(P<0.05). Logistic regression analysis showed that the risk of subclinical hypothyroidism in women with UIC≥250 μg/L was increased by 3.498 fold(95%CI 1.588-7.704)as compared with those with 150≤UIC<250 μg/L. The risk of subclinical hypothyroidism in women with blood selenium <80 μg/L was increased by 2.667 fold(95%CI 1.123-6.331)compared with those with 90≤selenium <100 μg/L. After adjusting for age, gestational weeks, residential district, TPOAb, TgAb, taking compound nutritional supplements, more-than-adequate and excessive iodine still increased the risk of subclinical hypothyroidism(OR=3.014, 95%CI 1.310-6.938). Women with UIC≥250 μg/L and blood selenium <95 μg/L revealed the increased risk of subclinical hypothyroidism as compared to those with 150≤UIC<250 μg/L and selenium≥95 μg/L(OR=5.429, 95%CI 1.929-15.281). After adjusting for age, gestational weeks, residential district, TPOAb, TgAb, taking compound nutritional supplements, the fingdings still existed. Conclusion The nutrient condition of iodine and selenium of the pregnant women in Tianjin during the first half pregnancy should be noticed. The individualized supplement of iodine and selenium, if needed, should be performed to decrease the risk of subclinical hypothyroidism. (Chin J Endocrinol Metab, 2018, 34: 38-43) Key words: The first half of pregnancy; Subclinical hypothyroidism; Thyroid antibodies; Urinary iodine; Blood selenium