Urinary iodine, thyroid function, and thyroglobulin as biomarkers of iodine status

Current iodine nutrition status in Poland (2017): is the Polish model of obligatory iodine prophylaxis able to eliminate iodine deficiency in the population?

OBJECTIVE

The monitoring of the populations' iodine status is an essential part of successful programmes of iodine deficiency elimination. The current study aimed at the evaluation of current iodine nutrition in school children, pregnant and lactating women as a marker of the effectiveness and sustainability of mandatory iodine prophylaxis in Poland.

DESIGN

The following iodine nutrition indicators were used: urinary iodine concentration (UIC) (all participants) and serum thyroglobulin (pregnant and lactating women).

SETTING

The study was conducted in 2017 within the National Health Programme in five regions of Poland.

PARTICIPANTS

The research included 300 pregnant women, 100 lactating women and 1000 school children (aged 6-12 years).

RESULTS

In pregnant women, median UIC was 111·6 µg/l; there was no significant difference in median UIC according to the region of residence. In 8 % of pregnant women, thyroglobulin level was >40 ng/ml (median thyroglobulin 13·3 ng/ml). In lactating women, median UIC was 68·0 µg/l. A significant inter-regional difference was noted (P = 0·0143). In 18 % of breastfeeding women, thyroglobulin level was >40 ng/ml (median thyroglobulin 18·5 ng/ml). According to the WHO criteria, the investigated sample of pregnant and lactating women was iodine-deficient. Median UIC in school children was 119·8 µg/l (with significant inter-regional variation; P = 0·0000), which is consistent with iodine sufficiency. Ninety-four children (9·4 %) had UIC < 50 µg/l.

CONCLUSIONS

Mandatory iodisation of household salt in Poland has led to a sustainable optimisation of iodine status in the general population. However, it has failed to assure adequate iodine nutrition during pregnancy and lactation.

Vegans, Vegetarians, and Omnivores: How Does Dietary Choice Influence Iodine Intake? A Systematic Review

Vegan and vegetarian diets are becoming increasingly popular. Dietary restrictions may increase the risk of iodine deficiency. This systematic review aims to assess iodine intake and status in adults following a vegan or vegetarian diet in industrialised countries. A systematic review and quality assessment were conducted in the period May 2019-April 2020 according to Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Studies were identified in Ovid MEDLINE, Embase, Web of Science, PubMed, Scopus, and secondary sources. Fifteen articles met inclusion criteria. Participants included 127,094 adults (aged ≥ 18 years). Vegan groups presented the lowest median urinary iodine concentrations, followed by vegetarians, and did not achieve optimal status. The highest iodine intakes were recorded in female vegans (1448.0 ± 3879.0 µg day-1) and the lowest in vegetarians (15.6 ± 21.0 µg day-1). Omnivores recorded the greatest intake in 83% of studies. Seaweed contributed largely to diets of vegans with excessive iodine intake. Vegans appear to have increased risk of low iodine status, deficiency and inadequate intake compared with adults following less restrictive diets. Adults following vegan and vegetarian diets living in countries with a high prevalence of deficiency may be more vulnerable. Therefore, further monitoring of iodine status in industrialised countries and research into improving the iodine intake and status of adults following vegan and vegetarian diets is required.

Prevalence of thyroid dysfunction in healthy adults according to the estimated iodine intake in 24-hour urine samples: The SALMEX cohort

PURPOSE

The aim of this study was to evaluate the prevalence of thyroid dysfunction in a cohort of healthy individuals in Mexico City, as well as to investigate the potential associations of these results with their estimated iodine intake (EII) as reflected by their 24-hour urinary iodine excretion (24-h UIE).

METHODS

From the SALMEX cohort, 683 adults provided an appropriate 24-h urine sample. Thyroid function tests and thyroid antibody concentrations were determined in the participants' sera. We analyzed discrepancies between the commonly used urinary parameters to determine the iodine intake status and the performance of thyroglobulin (Tg) as a biomarker of its status in the adult population.

RESULTS

The prevalence of dysthyroidism was high, being similar to other studies. Subclinical hypothyroidism was detected in 5.0% of individuals, clinical hypothyroidism in 1.8% of individuals, and sub-clinical hyperthyroidism in 2.8% of individuals. The median EII was 285 μg/d (IQR 215.0-369.0); 94% of individuals had EII >150 µg/d recommended daily allowance (RDA) in adults. The urinary iodine concentration (UIC) and the UIE had relative biases in their averages of 34.4%. The Tg median was 7.21 ng/mL. The prevalence of increased Tg was 6.15%. There was no correlation between Tg and EII (r= 0.019, p= 0.606).

CONCLUSIONS

Thyroid dysfunction was highly prevalent in this population. Our cohort revealed a slight discrepancy between dysthyroidism manifestations and iodine intake markers; the latter represent a population with adequate iodine intake. Further studies are necessary to clearly define the prevalence of thyroid dysfunction as well as the iodine nutritional status in Mexico.

Thyroglobulin Concentration and Maternal Iodine Status During Pregnancy: A Systematic Review and Meta-Analysis

Background: Literature to date has been inconclusive regarding the value of thyroglobulin (Tg) as a marker of iodine status in pregnant women. This systematic review and meta-analysis is one of the first to assess whether Tg concentration accurately reflects iodine status among pregnant women. Methods: We searched MEDLINE, the Web of Science, the Cochrane Library, Scopus, and other relevant databases to identify relevant studies published in the English language, between January 1988 and December 2018. The criteria for study inclusion in the systematic review were human studies, healthy pregnant women as participants, and available data for maternal urinary iodine concentration (UIC) and Tg level. Each study was assessed for quality and risk of bias. The pooled mean Tg values, and 95% confidence intervals were estimated in a population of women with UIC <150 and UIC ≥150 μg/L during pregnancy. Potential linear or nonlinear dose-response associations between maternal UIC and Tg concentration were examined. Results: Of 814 identified studies, 25 were eligible for inclusion in the meta-analysis. Studies included were conducted in Africa, Asia, Europe, South America, and the Oceania. The pooled mean (95% confidence interval [CI]) Tg concentration in iodine-deficient pregnant women was higher than that in iodine-sufficient pregnant women (10.73 μg/L [5.65-15.82] vs. 7.34 μg/L [2.20-12.47]); a comparison of the 95% CI showed that none of these values was significantly different. No significant differences were observed in Tg concentration between the two groups in each trimester of pregnancy. Dose-response meta-analyses revealed a significant nonlinear association between maternal UIC and Tg concentration during pregnancy. Among populations of pregnant women, an inverse association was found between UIC values <100 μg/L and Tg concentration (p-linearity = 0.007; p-nonlinearity = 0.027); however, higher values of UIC were not associated with Tg concentration. Conclusions: Our meta-analysis showed that Tg concentration can be a sensitive indicator of iodine deficiency, specifically in populations of pregnant women with median UIC <100 μg/L. Further studies are warranted to determine the sensitivity of Tg at different degrees of iodine deficiency during pregnancy.

Low intake of iodized salt and iodine containing supplements among pregnant women with apparently insufficient iodine status - time to change policy?

BACKGROUND

Iodine is an essential nutrient for human health throughout the life cycle, especially during early stages of intrauterine life and infancy, to ensure adequate neurocognitive development. The growing global reliance on desalinated iodine-diluted water raises the specter of increased iodine deficiency in several regions. The case of Israel may be instructive for exploring the link between iodine status and habitual iodine intake in the setting of extensive national reliance on desalinated water. The aim of this study was to explore the relationship between iodine intake, including iodized salt and iodine-containing supplements intake, and iodine status among pregnant women residing in a sub-district of Israel that is highly reliant on desalinated iodine-diluted water.

METHODS

A total of 134 consecutive pregnant women were recruited on a voluntary basis from the obstetrics department of the Barzilai University Medical Center during 2018. Blood was drawn from participants to determine levels of serum thyrotropin (TSH), thyroid peroxidase antibodies (TPOAb), thyroglobulin antibodies (TgAb) and thyroglobulin (Tg). An iodine food frequency questionnaire (sIFFQ) was used to assess iodine intake from food, IS and ICS. A questionnaire was used to collect data on demographic and health characteristics.

RESULTS

A total of 105 pregnant women without known or reported thyroid disease were included in the study. Elevated Tg values (≥ 13 μg/L), were found among 67% of participants, indicating insufficient iodine status. The estimated iodine intake (median, mean ± SD 189, 187 ± 106 μg/d by sIFFQ) was lower than the levels recommended by the World Health Organization and the Institute of Medicine (250 vs. 220 μg/day respectively). The prevalence of iodized salt intake and iodine containing supplement intake were 4 and 52% (respectively). Values of Tg > 13 μg/L were inversely associated with compliance with World Health Organization and Institute of Medicine recommendations.

CONCLUSIONS

While the Israeli Ministry of Health has recommended the intake of iodized salt and iodine containing supplements, this is apparently insufficient for achieving optimal iodine status among Israeli pregnant women. The evidence of highly prevalent probable iodine deficiency in a sample of pregnant women suggests an urgent need for a national policy of iodized salt regulation, as well as guidelines to promote iodine containing supplements and adherence to them by caregivers. In addition, studies similar to this one should be undertaken in additional countries reliant on desalinated iodine-diluted water to further assess the impact of desalinization on maternal iodine status.

Iodine Deficiency and Supplementation in Pregnancy

Iodine deficiency during pregnancy is an important global public health issue and the leading preventable cause of neurodevelopmental impairments worldwide. The effects of severe iodine deficiency during pregnancy, including adverse obstetric outcomes and decreased child intelligence quotient, have been clearly established. However, the effects of mild-to-moderate deficiency remain less well understood. Pregnant and lactating women have higher iodine requirements than other adults; intakes of 220 to 250 µg/d in pregnancy and 250 to 290 µg/d in lactation. In this article, we describe iodine metabolism, iodine requirements in pregnancy and lactation, the effects of both iodine deficiency and excessive iodine intakes in pregnancy, and the efficacy of iodine supplementation.

Longitudinal Changes of One-Carbon Metabolites and Amino Acid Concentrations during Pregnancy in the Women First Maternal Nutrition Trial

BACKGROUND

Maternal dietary restriction and supplementation of one-carbon (1C) metabolites can impact offspring growth and DNA methylation. However, longitudinal research of 1C metabolite and amino acid (AA) concentrations over the reproductive cycle of human pregnancy is limited.

OBJECTIVE

To investigate longitudinal 1C metabolite and AA concentrations prior to and during pregnancy and the effects of a small-quantity lipid-based nutrition supplement (LNS) containing >20 micronutrients and prepregnancy BMI (ppBMI).

METHODS

This study was an ancillary study of the Women First Trial (NCT01883193, clinicaltrials.gov) focused on a subset of Guatemalan women (n = 134), 49% of whom entered pregnancy with a BMI ≥25 kg/m2. Ninety-five women received LNS during pregnancy (+LNS group), while the remainder did not (-LNS group). A subset of women from the Pakistan study site (n = 179) were used as a replication cohort, 124 of whom received LNS. Maternal blood was longitudinally collected on dried blood spot (DBS) cards at preconception, and at 12 and 34 wk gestation. A targeted metabolomics assay was performed on DBS samples at each time point using LC-MS/MS. Longitudinal analyses were performed using linear mixed modeling to investigate the influence of time, LNS, and ppBMI.

RESULTS

Concentrations of 23 of 27 metabolites, including betaine, choline, and serine, changed from preconception across gestation after application of a Bonferroni multiple testing correction (P < 0.00185). Sixteen of those metabolites showed similar changes in the replication cohort. Asymmetric and symmetric dimethylarginine were decreased by LNS in the participants from Guatemala. Only tyrosine was statistically associated with ppBMI at both study sites.

CONCLUSIONS

Time influenced most 1C metabolite and AA concentrations with a high degree of similarity between the 2 diverse study populations. These patterns were not significantly altered by LNS consumption or ppBMI. Future investigations will focus on 1C metabolite changes associated with infant outcomes, including DNA methylation. This trial was registered at clinicaltrials.gov as NCT01883193.

Establishing reference intervals for urine and serum iodine levels: A nationwide multicenter study of a euthyroid Chinese population

CONTEXT

Urinary iodine (UI) is commonly used for evaluating iodine status, whereas serum iodine (SI) is more closely correlated with bioavailable iodine. However, no reliable reference intervals (RIs) for clinical use are available. We aimed to establish RIs for SI, UI, and a ratio of UI to urinary creatinine (U-Cre) applicable to the Chinese population.

METHODS

This multicenter cross-sectional study enrolled 930 apparently healthy adults from six representative cities in China (Beijing, Dongying, Guiyang, Urumqi, Shenzhen, and Qiqihar) in 2017. Thyroid ultrasonography and thyroid function tests, including antithyroid antibody tests, were performed to exclude individuals with latent thyroid diseases. An iodine intake-related questionnaire survey was performed. SI and UI were measured using inductively coupled plasma-mass spectrometry. Possible influencing factors of iodine levels were evaluated using multiple regression analysis.

RESULTS

Post-exclusion, the final analysis included 894 individuals. Seafood intake frequency was positively correlated with SI (standardized partial regression coefficient = 0.23) but not with UI and UI/U-Cre. SI was positively correlated with serum TT4 (Spearman correlation coefficient: 0.40), TT3 (0.23), and FT4 (0.18). SI and UI showed no age- or sex-specific variations. Significantly higher UI/U-Cre values were observed in Qiqihar than in Beijing, Guizhou, and Shenzhen. Shenzhen showed the lowest UI levels among all evaluated cities. With application of latent abnormal values exclusion procedurere, the RIs for SI, UI, and UI/U-Cre in the population were 36.0-79.3 μg/L, 19-385 μg/L, 22-450 μg/g, respectively.

CONCLUSIONS

We established RIs for UI and SI among healthy Chinese individuals with no thyroid nodule or dysfunction.

Selenium and iodine in diabetes mellitus with a focus on the interplay and speciation of the elements

Diabetes mellitus is a chronic metabolic disease caused by insulin deficiency (type I) or dysfunction (type II). Diabetes is a threatening public health concern. It is considered as one of the priority non-communicable diseases, due to its high and increasing incidence, the associated healthcare costs, and threatening medical complications. Two trace elements selenium (Se) and iodine (I) were intensively discussed in the context of diabetic pathology and, possibly, etiology. It seems there is a multilayer involvement of these essential nutrients in glucose tolerance, energy metabolism, insulin signaling and resistance, which are mainly related to the antioxidant selenoenzymes and the thyroid hormones. Other factors might be related to (auto)immunity, protection against endoplasmic reticulum stress, and leptin signaling. The aim of the current review is to evaluate the current understanding of the role of selenium and iodine in diabetes with a focus on the biochemical interplay between the elements, their possible role as biomarkers, and their chemical speciation. Possible impacts from novel analytical techniques related to trace element speciation and isotopic analysis are outlined.

The efficiency of Governmental and WFP UN Programs for improvement of nutritional status in Tajik schoolchildren as assessed by dietary intake and hair trace element content

BACKGROUND

The objective of the study was to assess hair trace element and mineral content in children undergoing WFP UN and the governmental programs of school nutrition in Tajikistan.

METHODS

WFP program included provision or wheat flour fortified with micronutrients including Fe and Zn, and iodized salt, whereas within the governmental program hot meals were provided. A total of 202 children studying in schools that were not (Type 1, n = 100) or were involved in dietary intervention programs (Type 2, n = 102). Food and hair trace element content was assessed using ICP-MS.

RESULTS

Daily intake of Fe, I, Zn, B, Co, Mg, Si, and Sr in Type 2 schools was more than 2.5, 12, 4, 2.9, 2.6, 2, 3, and 2-fold higher than that in Type 1 schools. Correspondingly, anthropometric parameters in children from Type 2 schools exceeded the control values. Surprisingly, no significant difference in hair iodine levels was detected. Hair analysis demonstrated a significant increase in hair Ca, Mg, Na, Co, Cr, Cu, Fe, Li, Mn, Se, V, Zn content. Certain toxic elements including Al, As, and Be were also characterized by an increase in Type 2 schools. At the same time, nutritional intervention was associated with a significant decrease in hair B, Hg, and Sn levels.

CONCLUSIONS

Nutritional intervention within WFP and the governmental program was effective in increasing essential trace element supply in Tajik schoolchildren. However, further studies including a detailed assessment of nutritional and health status with a special focus on iodine and thyroid functioning are required.

The joint role of thyroid function and iodine concentration on gestational diabetes risk in a population-based study

INTRODUCTION

Iodine is essential for thyroid function, and iodine deficiency during pregnancy is common in Europe and the USA. However, no published studies have examined the role of iodine deficiency in the relation between thyroid function and gestational diabetes mellitus (GDM).

MATERIAL AND METHODS

We conducted a population-based, nested case-control study within the Finnish Maternity Cohort using pregnancy and perinatal outcome data from the Finnish Maternal Birth Register. We randomly selected 224 GDM cases with singleton pregnancies and 224 controls without GDM from all singleton births occurring in Finland during 2012-2013. Blood was drawn at 10-14 weeks' gestation and analyzed for serum iodide, thyroglobulin, and thyroid-stimulating hormone (TSH) concentrations. Logistic regression was used to estimate odds ratios (ORs) and 95% confidence intervals (CI) of GDM.

RESULTS

Very high thyroglobulin concentration (>95% percentile; >83 μg/L) was not associated with significantly altered odds of GDM compared to those with normal levels (OR 0.41; 95% CI: 0.12, 1.38). High concentrations of TSH were also not associated with increased odds of GDM compared to normal levels of TSH (OR 0.45; 95% CI: 0.06, 3.18). Women in the lowest 5th percentile (<1.58 ng/mL) of iodine did not have increased odds of GDM compared to those with iodide in the highest quartile (OR 0.39; 95% CI: 0.11, 1.35).

CONCLUSIONS

Low levels of iodide and thyroid function in early pregnancy are not associated with increased risk of GDM in this mildly iodine-deficient population.

Associations between urinary iodine concentration, lipid profile and other cardiometabolic risk factors in adolescents: a cross-sectional, population-based analysis

Low urinary iodine concentration (UIC) is associated with dyslipidaemia in adults but is not well characterised in adolescents. Because dyslipidaemia is a cardiovascular risk factor, identifying such an association in adolescents would allow for the prescription of appropriate measures to maintain cardiovascular health. The present study addresses this question using data in the 2001-2012 National Health and Nutrition Examination Survey for 1692 adolescents aged 12-19 years. Primary outcomes were UIC, cardiometabolic risk factors and dyslipidaemia. Data for subjects categorised by low and normal UIC and by sex were analysed by univariate and multivariate logistic regression. Treating UIC as the independent variable, physical activity level, apoB and lipid profiles differed significantly between subjects with low and normal UIC. Subjects with low UIC had a significantly greater risk of elevated total cholesterol (TC) (95 % CI 1·37, 2·81), elevated non-HDL (95 % CI 1·33, 2·76) and elevated LDL (95 % CI 1·83, 4·19) compared with those with normal UIC. Treating UIC as a dependent variable, the risk of low UIC was significantly greater in those with higher apoB (95 % CI 1·52, 19·08), elevated TC (≥4·4mmol/l) (95 % CI 1·37, 2·81) and elevated non-HDL (≥3·11mmol/l) (95 % CI 1·33, 2·76) than in those with normal UIC. These results show that male and female adolescents with low UIC tend to be at greater risk of dyslipidaemia and abnormal cardiometabolic biomarkers, though the specific abnormal parameters differed between sexes. These results may help to identify youth who would benefit from interventions to improve their cardiometabolic risk.

Iodine status of euthyroid adults: A cross-sectional, multicenter study

Background

Iodine, an essential nutrient, is the most important trace element in thyroid hormone synthesis and maintenance of thyroid function. This study investigated the iodine nutrition status in healthy Chinese adults and assessed the relationship between urinary iodine concentration (UIC) and thyroid hormone levels.

Methods

A cross‐sectional, multicenter study was conducted between October 2017 and January 2018, with 1017 adults recruited from five cities in China. All subjects underwent thyroid ultrasonography, and only those with normal results were included in the study. UICs were measured by inductively coupled plasma mass spectroscopy and adjusted using urine creatinine levels. Thyroid hormone levels were measured using an automated immunoassay analyzer.

Results

The median UIC and adjusted UIC were 134.0 µg/L and 114.2 µg/g, respectively. UIC was not significantly different between males and females (P = 0.737). However, the adjusted UIC was significantly different between sexes (P < 0.001). The median UIC was higher than 100 µg/L. According to the World Health Organization criterion (100 µg/L), the total prevalence of iodine deficiency is 33.1% (n = 271). The prevalence rates of iodine deficiency in our study were 33.2% and 32.9% in males and females, respectively, and had no difference between sexes and among cities (P > 0.05). Serum thyroid‐stimulating hormone (TSH) levels increased when UIC increased. The Kruskal‐Wallis test showed no significant differences in free triiodothyronine, free thyroxine, and TSH, with different levels of UIC (all P > 0.05).

Conclusions

Chinese adults with normal thyroid structure have relatively sufficient iodine levels.

A Comparative Study of Iodized Salt Programs: Shanghai and Switzerland

Both Shanghai and Switzerland are developed regions with long-standing salt iodization programs and periodic monitoring. However, the two regions have their own approach to the implementation of the iodized salt policy. In Shanghai, monitoring was carried out every few years, using probability-proportional-to-size sampling technique to select 30 sampling units. Each unit consisted of more than 12 pregnant women and one randomly selected primary school. Urine samples were then taken from the chosen pregnant women and randomly recruited students of that school for iodine test. Data of Switzerland used in this comparative study was extracted from published researches. In Shanghai, the median urinary iodine concentration (UIC) in 2014 was 20% lower than in 1999 (P < 0.05). The median UIC of pregnant women in 2014 was 9.5% lower than that in 2011 (P < 0.05). In terms of iodized salt concentration, opposite to the increasing in Switzerland, it has exhibited a downward trend in Shanghai (P < 0.05). For the years monitored, the iodized salt concentration in Shanghai was significantly (P < 0.05) higher than in Switzerland. Though the UIC of children exhibited a downward trend in Shanghai (P < 0.05), it was still significantly (P < 0.05) higher than in Switzerland over the same monitoring period. However, the UIC in pregnant women was a totally different story, which was significantly (P < 0.05) lower in Shanghai than in Switzerland. Iodized salt is very important for maintaining sufficient iodine level in the population. Appropriate concentration of iodine in fortified salt needs to be decided according to local conditions. Special attention should be paid to the iodine level of pregnant women in Shanghai, and more education about iodine is necessary for the public health.

Fluoride exposure and thyroid function among adults living in Canada: Effect modification by iodine status

BACKGROUND

Fluoride exposure has the potential to disrupt thyroid functioning, though adequate iodine intake may mitigate this effect. This is the first population-based study to examine the impact of chronic low-level fluoride exposure on thyroid function, while considering iodine status. The objective of this study was to determine whether urinary iodine status modifies the effect of fluoride exposure on thyroid stimulating hormone (TSH) levels.

METHODS

This cross-sectional study utilized weighted population-based data from Cycle 3 (2012-2013) of the Canadian Health Measures Survey (CHMS). Information was collected via a home interview and a visit to a mobile examination centre. The weighted sample represented 6,914,124 adults in Canada aged 18-79 who were not taking any thyroid-related medication. Urinary fluoride concentrations were measured in spot samples using an ion selective electrode and adjusted for specific gravity (UF_SG). Serum TSH levels provided a measure of thyroid function. Multivariable regression analyses examined the relationship between UF_SG and TSH, controlling for covariates.

RESULTS

Approximately 17.8% of participants fell in the moderately-to-severely iodine deficient range. The mean (SD) age of the sample was 46.5 (15.6) years and the median UF_SG concentration was 0.74 mg/L. Among iodine deficient adults, a 1 mg/L increase in UF_SG was associated with a 0.35 mIU/L increase in TSH [95% CI: 0.06, 0.64; p = 0.01, one-tailed].

CONCLUSIONS

Adults living in Canada who have moderate-to-severe iodine deficiencies and higher levels of urinary fluoride may be at an increased risk for underactive thyroid gland activity.

Language delay and poorer school performance in children of mothers with inadequate iodine intake in pregnancy: results from follow-up at 8 years in the Norwegian Mother and Child Cohort Study

Purpose

Some studies indicate that mild-to-moderate iodine deficiency in pregnant women might negatively affect offspring neurocognitive development, including previous results from the Norwegian Mother and Child Cohort study (MoBa) exploring maternally reported child development at age 3 years. The aim of this follow-up study was to investigate whether maternal iodine intake in pregnancy is associated with language and learning at 8 years of age.

Methods

The study sample includes 39,471 mother–child pairs participating in MoBa with available information from a validated food frequency questionnaire covering the first half of pregnancy and a questionnaire on child neurocognitive development at 8 years. Multivariable regression was used to explore associations of iodine intake from food and supplements with maternally reported child outcomes.

Results

Maternal iodine intake from food less than ~ 150 µg/day was associated with poorer child language skills (p-overall = 0.013), reading skills (p-overall = 0.019), and writing skills (p-overall = 0.004) as well as poorer school test result in reading (p < 0.001), and increased likelihood of the child receiving special educational services (p-overall = 0.042) (in non-iodine supplement users). Although significant, differences were generally small. Maternal use of iodine supplements in pregnancy was not significantly associated with any of the outcomes.

Conclusions

Low habitual iodine intake in pregnant women, i.e., lower than the recommended intake for non-pregnant women, was associated with mothers reporting poorer child language, school performance, and increased likelihood of special educational services. We found no indications of benefits or harm of using iodine-containing supplements in pregnancy. Initiating use in pregnancy might be too late.

Electronic supplementary material

The online version of this article (10.1007/s00394-018-1850-7) contains supplementary material, which is available to authorized users.

Data on spot-kits versus titration method for iodine determination in salt: Performance and validity

The aim of this data is comparison of achieved data from salt iodine measurement by titration method with using sodium thiosulfate in presence of lugol׳s reagent and commercial spot- kit. Titration measurement was carried out in two different laboratories using standard samples. 437 samples including 20 commercial brands were collected throughout Iran. The iodine contents of the samples were measured by both the titration method and two most frequently used spot-kit brands in Iran. There is no significant differences between the results obtained from the two brands of spot-kits (ICC = 0.797). The kits sensitivity for determination of negative samples was high (more than 0.9) but by increasing the iodine concentration up to 15 ppm, the kits’ sensitivity was decreased. These findings indicate that the titration method is necessary for quantitative purposes, especially for concentrations higher than 30 ppm. However, spot-kits are suitable for qualitative and semi-quantitative measurements.

Maternal Iodine Status is Associated with Offspring Language Skills in Infancy and Toddlerhood

Inadequate iodine status affects the synthesis of the thyroid hormones and may impair brain development in fetal life. The aim of this study was to explore the association between maternal iodine status in pregnancy measured by urinary iodine concentration (UIC) and child neurodevelopment at age 6, 12 and 18 months in a population-based cohort. In total, 1036 families from nine locations in Norway were enrolled in the little in Norway cohort. The present study includes n = 851 mother-child pairs with singleton pregnancies, no use of thyroid medication in pregnancy, no severe genetic disorder, data on exposure (UIC) in pregnancy and developmental outcomes (Bayley Scales of Infant and Toddler Development, third edition). Data collection also included general information from questionnaires. We examined associations between UIC (and use of iodine-containing supplements) and repeated measures of developmental outcomes using multivariable mixed models. The median UIC in pregnancy was 78 µg/L (IQR 46⁻130), classified as insufficient iodine intake according to the WHO. Eighteen percent reported use of iodine-containing multisupplements. A UIC below ~100 was associated with reduced receptive (p = 0.025) and expressive language skills (p = 0.002), but not with reduced cognitive or fine- and gross motor skills. Maternal use of iodine-containing supplements was associated with lower gross motor skills (b = -0.18, 95% CI = -0.33, -0.03, p = 0.02), but not with the other outcome measures. In conclusion, an insufficient iodine intake in pregnancy, reflected in a UIC below ~100 µg/L, was associated with lower infant language skills up to 18 months. The use of iodine-containing supplements was not associated with beneficial effects.

Current state of iodine nutrition in Filipino school-aged children

OBJECTIVES

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.

METHODS

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.

RESULTS

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.

CONCLUSION

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.

Development of Databases on Iodine in Foods and Dietary Supplements

Iodine is an essential micronutrient required for normal growth and neurodevelopment; thus, an adequate intake of iodine is particularly important for pregnant and lactating women, and throughout childhood. Low levels of iodine in the soil and groundwater are common in many parts of the world, often leading to diets that are low in iodine. Widespread salt iodization has eradicated severe iodine deficiency, but mild-to-moderate deficiency is still prevalent even in many developed countries. To understand patterns of iodine intake and to develop strategies for improving intake, it is important to characterize all sources of dietary iodine, and national databases on the iodine content of major dietary contributors (including foods, beverages, water, salts, and supplements) provide a key information resource. This paper discusses the importance of well-constructed databases on the iodine content of foods, beverages, and dietary supplements; the availability of iodine databases worldwide; and factors related to variability in iodine content that should be considered when developing such databases. We also describe current efforts in iodine database development in the United States, the use of iodine composition data to develop food fortification policies in New Zealand, and how iodine content databases might be used when considering the iodine intake and status of individuals and populations.

The application of serum iodine in assessing individual iodine status

CONTEXT

The prevalence of thyroid disease in China is on the rise, and this could be partly associated with excessive iodine intake in some individuals; therefore, increased attention is being paid to individual iodine status. However, current indices are not appropriate for evaluating individual iodine status.

OBJECTIVE

To evaluate the association between serum iodine and urinary iodine (UI), as well as thyroid diseases, and provide an excellent base for future individual iodine status assessment.

DESIGN, SUBJECTS AND MEASUREMENTS

A total of 902 adults were enrolled in this study including 325, 286 and 291 subjects from regions in China where iodine is adequate, sufficient and in excess, respectively. Serum iodine, UI and thyroid function were assessed, and ultrasonography performed in all subjects.

RESULTS

The median serum iodine values of adults with subclinical hypothyroidism, high serum autoantibody and thyroid nodules were significantly higher than those of euthyroid adults (P<0.05). A serum iodine level higher than 100 μg/L was considered as a risk factor for thyroid diseases. Serum iodine had strong nonlinear correlations with UI and thyroid function. When thyroid function was taken as a gold standard, the area under the receiver operating characteristic (ROC) curve for serum iodine was 0.752 and UI was 0.507 for subjects with lower serum iodine and UI levels. The area for serum iodine was 0.773 and UI was 0.638 for subjects with higher serum iodine and UI levels. The areas under these curves were significantly different (P<0.001).

CONCLUSION

In adults, serum iodine had a strong nonlinear correlation with UI and a high level of serum iodine was a risk factor for thyroid diseases.

Variation in iodine food composition data has a major impact on estimates of iodine intake in young children

BACKGROUND/OBJECTIVES

The reliability of an estimate of iodine intake is largely dependent on the quality of the food composition data. We aimed to assess the impact of variations in food composition data for iodine and season on the estimates of iodine intake in young children.

SUBJECTS/METHODS

Cross-sectional dietary intake study of Irish 2-year-olds participating in the Cork BASELINE Birth Cohort Study (n=468; 30% of the cohort at the 2-year follow-up) were used to assess the impact of variation in iodine food composition data on estimates of iodine intake, dietary adequacy and risk of exceeding the tolerable upper intake level (UL).

RESULTS

Mean (SD) iodine intakes calculated using UK (147 (71)) and Irish (177 (93)) food composition data were significantly different (P < 0.001) (mean difference (95% confidence interval) = 30 (26-33) µg/day) and largely adequate (7-14% below the estimated average requirement). Intakes at the 95th percentile were 138% and 173% of the UL using UK and Irish food composition data, respectively, of which milk accounted for 106% and 150% of the UL. This translated into 22% and 35% of toddlers exceeding the UL, using UK and Irish composition data, respectively. The mean (SD) daily intake of cow's milk among the 91% of consumers was 309 (208) ml. Intakes of cow's milk at the 75th and 95th percentiles were 452 and 706 ml, respectively. Using Irish composition data for iodine in cows' milk, a daily intake of 450 ml could result in a toddler exceeding the UL from milk alone.

CONCLUSIONS

Variability in food composition has a large impact on assessments of iodine intake, particularly among young children for whom milk contributes a large proportion of their daily nutrient intake. Although this is unlikely to result in long-term adverse effects, our study highlights the need for development of valid biomarkers of individual iodine status.

Reliability of thyroglobulin in serum compared with urinary iodine when assessing individual and population iodine nutrition status

The occurrence of thyroid disorders relies on I nutrition and monitoring of all populations is recommended. Measuring I in urine is standard but thyroglobulin in serum is an alternative. This led us to assess the reliability of studies using serum thyroglobulin compared with urinary I to assess the I nutrition level and calculate the number of participants needed in a study with repeated data sampling in the same individuals for 1 year. Diet, supplement use and life style factors were assessed by questionnaires. We measured thyroglobulin and thyroglobulin antibodies in serum and I in urine. Participants were thirty-three Caucasians and sixty-four Inuit living in Greenland aged 30–49 years. Serum thyroglobulin decreased with rising I excretion (Kendall’sτ−0·29,P=0·005) and did not differ with ethnicity. Variation in individuals was lower for serum-thyroglobulin than for urinary I (mean individual CV: 15·1v. 46·1 %;P<0·01). It required 245 urine samples to be 95 % certain of having a urinary I excretion within 10 % of the true mean of the population. For serum-thyroglobulin the same precision required 206 samples. In an individual ten times more samples were needed to depict I deficiency when using urinary I excretion compared with serum-thyroglobulin. In conclusion, more participants are need to portray I deficiency in a population when using urinary I compared with serum-thyroglobulin, and about ten times more samples are needed in an individual. Adding serum-thyroglobulin to urinary I may inform surveys of I nutrition by allowing subgroup analysis with similar reliability.

Assessing infant cognitive development after prenatal iodine supplementation

Little information is available on infant behavioral development outcomes of prenatal iodine supplementation in regions of mild to moderate iodine deficiency. Studies performed to date, all of which relied on global developmental assessments, have yielded inconsistent findings with regard to psychomotor development, negative findings with regard to mental development, and no information as to the development of specific cognitive functions. Our review of these studies leads us to suspect that the use of global developmental assessments might partially explain the negative and inconsistent findings. To identify cognitive processes that might be sensitive to prenatal iodine supplementation, we examined the timing of thyroid hormone action on specific brain systems. The development of infant visual attention is sensitive to thyroid hormone during the early prenatal period, when the fetus is entirely dependent on maternal thyroid hormone. For this reason, infant visual attention has the potential to be a sensitive measure of infant outcomes in prenatal iodine supplementation studies. We suggest the assessment of infant visual attention, with follow-up examination of childhood executive functions, as a means of capturing the effects of maternal iodine deficiency and prenatal iodine supplementation on specific cognitive processes. In particular, we propose comparison of infant performance on global developmental tests and specialized tests of visual attention in pilot trials of prenatal iodine supplementation in regions of mild to moderate iodine deficiency. Only by comparing the 2 types of tests side by side will it be possible to establish whether the use of a sensitive measure of infant visual attention will increase the reliability of such supplementation studies. Recognizing that exposure misclassification may also provide a partial explanation for the inconsistent neurodevelopmental outcomes in previous studies, we suggest that urinary iodine concentration or creatinine-corrected iodine excretion be monitored regularly in such trials throughout the prenatal period.

Research needs for assessing iodine intake, iodine status, and the effects of maternal iodine supplementation

The Office of Dietary Supplements of the NIH convened 3 workshops on iodine nutrition in Rockville, Maryland, in 2014. The purpose of the current article is to summarize and briefly discuss a list of research and resource needs developed with the input of workshop participants. This list is composed of the basic, clinical, translational, and population studies required for characterizing the benefits and risks of iodine supplementation, along with related data, analyses, evaluations, methods development, and supporting activities. Ancillary studies designed to use the participant, biological sample, and data resources of ongoing and completed studies (including those not originally concerned with iodine) may provide an efficient, cost-effective means to address some of these research and resource needs. In the United States, the foremost question is whether neurobehavioral development in the offspring of mildly to moderately iodine-deficient women is improved by maternal iodine supplementation during pregnancy. It is important to identify the benefits and risks of iodine supplementation in all population subgroups so that supplementation can be targeted, if necessary, to avoid increasing the risk of thyroid dysfunction and related adverse health effects in those with high iodine intakes. Ultimately, there will be a need for well-designed trials and other studies to assess the impact of maternal supplementation on neurodevelopmental outcomes in the offspring. However, 2 basic information gaps loom ahead of such a study: the development of robust, valid, and convenient biomarkers of individual iodine status and the identification of infant and toddler neurobehavioral development endpoints that are sensitive to mild maternal iodine deficiency during pregnancy and its reversal by supplementation.

Development of Standard Reference Materials to support assessment of iodine status for nutritional and public health purposes

The use of urinary iodine as an indicator of iodine status relies in part on the accuracy of the analytical measurement of iodine in urine. Likewise, the use of dietary iodine intake as an indicator of iodine status relies in part on the accuracy of the analytical measurement of iodine in dietary sources, including foods and dietary supplements. Similarly, the use of specific serum biomarkers of thyroid function to screen for both iodine deficiency and iodine excess relies in part on the accuracy of the analytical measurement of those biomarkers. The National Institute of Standards and Technology has been working with the NIH Office of Dietary Supplements for several years to develop higher-order reference measurement procedures and Standard Reference Materials to support the validation of new routine analytical methods for iodine in foods and dietary supplements, for urinary iodine, and for several serum biomarkers of thyroid function including thyroid-stimulating hormone, thyroglobulin, total and free thyroxine, and total and free triiodothyronine. These materials and methods have the potential to improve the assessment of iodine status and thyroid function in observational studies and clinical trials, thereby promoting public health efforts related to iodine nutrition.

Suggested use of sensitive measures of memory to detect functional effects of maternal iodine supplementation on hippocampal development

Maternal hypothyroxinemia secondary to iodine deficiency may have neurodevelopmental effects on the specific neurocognitive domain of memory. Associated disruption of thyroid hormone-dependent protein synthesis in the hippocampus has the potential to result in compromised development of the structure with consequential impairments in memory function. Despite links between maternal iodine deficiency during gestation and lactation and abnormal hippocampal development in rat fetuses and pups, there has been little research on the specific function of memory in human infants and young children born to iodine-deficient mothers. Several candidate measures have proven to be sensitive to the effects of gestational iron deficiency on memory function in infants and young children, including habituation and dishabituation, imitation-based tasks, and event-related potentials. Such measures could be used to test the effects of maternal iodine supplementation on the specific neurocognitive domain of memory in infants and young children. Furthermore, progress in understanding the effects of maternal iodine supplementation on neurocognitive development could be accelerated by the development of a nonhuman primate model to complement the rodent model.

Comparison of 2 methods for estimating the prevalences of inadequate and excessive iodine intakes

BACKGROUND

Prevalences of iodine inadequacy and excess are usually evaluated by comparing the population distribution of urinary iodine concentration (UIC) in spot samples with established UIC cutoffs. To our knowledge, until now, dietary intake data have not been assessed for this purpose.

OBJECTIVE

Our objective was to compare 2 methods for evaluating the prevalence of iodine inadequacy and excess in sex- and life stage-specific subgroups of the US population: one that uses UIC cutoffs, and one that uses iodine intake cutoffs.

DESIGN

By using the iodine concentrations of foods measured in the US Food and Drug Administration's Total Diet Study (TDS), dietary intake data from the NHANES 2003-2010, and a file that maps each NHANES food to a TDS food with similar ingredients, we estimated each NHANES participant's iodine intake from each NHANES food as the mean iodine concentration of the corresponding TDS food in samples gathered over the same 2-y period. We calculated prevalences of iodine inadequacy and excess in each sex- and life stage-specific subgroup by both the UIC cutoff method and the iodine intake cutoff method-using the UIC values and dietary intakes reported for NHANES participants who provided both types of data-and compared the prevalences across methods.

RESULTS

We found lower prevalences of iodine inadequacy across all sex- and life stage-specific subgroups with the iodine intake cutoff method than with the UIC cutoff method; for pregnant females, the respective prevalences were 5.0% and 37.9%. For children aged ≤8 y, the prevalence of excessive iodine intake was high by either method.

CONCLUSIONS

The consideration of dietary iodine intake from all sources may provide a more complete understanding of population prevalences of iodine inadequacy and excess and thus better inform dietary guidance than consideration of UIC alone. Methods of adjusting UIC for within-person variation are needed to improve the accuracy of prevalence assessments based on UIC.

Consequences of iodine deficiency and excess in pregnant women: an overview of current knowns and unknowns

Severe iodine deficiency during development results in maternal and fetal hypothyroidism and associated serious adverse health effects, including cretinism and growth retardation. Universal salt iodization is the first-line strategy for the elimination of severe iodine deficiency. Iodine supplementation is recommended for vulnerable groups in severely iodine-deficient regions where salt iodization is infeasible or insufficient. A recent clinical trial has informed best practices for iodine supplementation of severely iodine-deficient lactating mothers. Because of successful programs of universal salt iodization in formerly severely iodine-deficient regions around the world, public health concern has shifted toward mild to moderate iodine deficiency, which remains prevalent in many regions, especially among pregnant women. Observational studies have shown associations between both mild maternal iodine deficiency and mild maternal thyroid hypofunction and decreased child cognition. Iodine supplementation has been shown to improve indexes of maternal thyroid function, even in marginally iodine-deficient areas. However, no data are yet available from randomized controlled trials in regions of mild to moderate iodine insufficiency on the relation between maternal iodine supplementation and neurobehavioral development in the offspring; thus, the long-term benefits and safety of such supplementation are uncertain. Although it is clear that excessive iodine intake can cause alterations in thyroid function in susceptible individuals, safe upper limits for iodine intake in pregnancy have not been well defined. Well-designed, prospective, randomized controlled trials that examine the effects of iodine supplementation on maternal thyroid function and infant neurobehavioral development in mildly to moderately iodine-deficient pregnant women are urgently needed. In addition, clinical data on the effects of iodine excess in pregnant and lactating women are needed to inform current recommendations for safe upper limits on chronic iodine ingestion in general and on iodine supplementation in particular.

Assessing iodine intake, iodine status, and the effects of maternal iodine supplementation: introduction to articles arising from 3 workshops held by the NIH Office of Dietary Supplements

The NIH Office of Dietary Supplements (ODS) convened 3 workshops on iodine nutrition in 2014, each held in Rockville, Maryland. These workshops were part of the ongoing ODS Iodine Initiative, begun in 2011 in response to concerns that US pregnant women may be at risk of iodine deficiency and that a high fraction of prenatal dietary supplements do not contain the recommended amounts of iodine. The primary purpose of the workshops was to consider the data and resources necessary to evaluate the clinical and public health benefits and risks of maternal iodine supplementation in the United States. The first workshop focused on the assessment of iodine intake, the second focused on the assessment of iodine status, and the third focused on the design and interpretation of clinical trials of maternal iodine supplementation. Here we provide the background of the ODS Iodine Initiative, summarize the 3 workshops held in 2014, and introduce the articles that arose from the workshops and are published in this supplement issue.