A comprehensive assessment of urinary iodine concentration and thyroid hormones in New Zealand schoolchildren: a cross-sectional study

Improving Iodine Status in Lactating Women: What Works?

PURPOSE OF REVIEW

Iodine deficiency is a global concern, and in recent years, there has been a significant improvement in the number of countries identified as being iodine-sufficient. This review considers the best strategies to ensure iodine sufficiency among breastfeeding women and their infants.

RECENT FINDINGS

Fortification strategies to improve iodine intake have been adequate for school-age children (SAC); however, often, iodine deficiency remains for breastfeeding women and their infants. Daily supplementation with iodine is not an ideal strategy to overcome deficiency. Countries defined as iodine-sufficient, but where pregnant and breastfeeding women have inadequate intake, should consider increasing salt iodine concentration, such that the median urinary iodine concentration of SAC can be up to 299 µg/L. This will ensure adequate intake for mothers and infants, without SAC being at risk thyroid dysfunction. Consensus is required for thresholds for iodine adequacy for breastfeeding women and infants.

Iodine, Thyroglobulin and Thyroid Gland

Iodine is essential in the biosynthesis of thyroid hormones that affect metabolic processes in the organism from the prenatal state to the elderly. The immediate indicator of iodine intake is the concentration of iodine in urine, but the indicator of iodine intake in the longer term of several months is thyroglobulin (Tg). Tg negatively correlated with increasing intake of iodine in population that do not suffer from thyroid disease, while a more than adequate to excessive iodine intake leads to an increase in Tg. The dependence of Tg on iodine can be described by a U-shaped curve. Thyroglobulin in serum is elevated in thyroid disease mainly in hyperthyroidism (diagnosis E05 of WHO ICD-10 codes) and in goiter (diagnosis E04 of WHO ICD-10 codes). Tg values decrease below 20 µg/l after effective treatment of patients with thyroid disease. Thyroglobulin may thus be an indicator of thyroid stabilization and the success of the thyroid gland treatment.

Urinary iodine levels of primary school children in Ilorin, Nigeria

Background: Iodine deficiency is one of the commonest micronutrient deficiencies. Globally, it is the commonest cause of preventable mental retardation and also associated with impaired physical growth. The current iodine nutrition of school children in Ilorin, North-Central Nigeria is not known. Objective: The study aimed to determine the urinary iodine levels(UIL) of school children in Ilorin and explored the relationship with socio-demographic variables. Methods: This cross-sectional study was carried out among primary schools children in Ilorin, Nigeria. We recruited school children aged 6-12 years through a multi-staged sampling method. Relevant data including socio-demographic variables were obtained with a pretested study proforma. The recruited school children had urinary iodine determined using the Sandell-Kolthoff method. Data analysis was with Statistical Package for Social Sciences version 20.0. Results: The median with interquartile range (IQR) of urinary iodine level was 117.2 (99.6-148.6) g/L. Of the 480 recruited children, 336 (70.0%) had normal urinary iodine levels while 144 (25%) had mild iodine deficiency and two (0.4%) had excess urinary iodine levels. Pupils with iodine deficiency was higher among public schools than those in private schools (33.3% vs 23.6%, 2 = 150.149, p < 0.022). The median UIL of the age-group 6-9 years was higher than the 10-12year age group (p = 0.026). However, the median UIL values were comparable across gender, socioeconomic strata and mother's educational level. Conclusions: This study showed that a quarter of the children still had mild iodine deficiency despite salt iodisation policy adopted by the country. Also, the iodine levels were not influenced by socio-demographics.

Iodized Salt Intake and Its Association with Urinary Iodine, Thyroid Peroxidase Antibodies, and Thyroglobulin Antibodies Among Urban Chinese

BACKGROUND

Whether iodized salt increases the risk of thyroid disease has been strongly debated in China, especially in the urban areas of coastal regions, in recent years. This study aimed to investigate the status of iodized salt in terms of urinary and serum iodine concentration in urban coastal areas, and to explore further whether consumption of iodized salt or non-iodized salt is associated with autoimmune thyroid disease (AITD).

METHODS

The data source was SPECT-China, a cross-sectional study in East China. A total of 1678 subjects were enrolled from 12 communities in downtown Shanghai. The type of salt consumed, the urinary iodine concentration (UIC), serum iodine, thyroid peroxidase antibodies (TPOAb), and thyroglobulin antibodies (TgAb) levels were obtained. AITD was defined as serum TPOAb and/or TgAb >60 kIU/L (TPO/TgAb [+]).

RESULTS

The prevalence of AITD was 10.5% in men and 21.4% in women. The median UIC and serum iodine concentration were 106.4 μg/L and 60.9 μg/L, respectively. Among all the subjects, 46.4% consumed non-iodized salt; the prevalence of iodine deficiency among those subjects was significantly higher than that of the subjects who consumed iodized salt (54.2% vs. 40.1%; p < 0.001). Consumption of non-iodized salt was positively associated with AITD in all participants (odds ratio [OR] = 1.49 [confidence interval (CI) 1.15-1.95]; p = 0.003) and in women (OR = 1.63 [CI 1.20-2.21]; p < 0.01) after multivariable adjustment. Additionally, the association between low UIC and AITD was observed among all subjects (OR = 1.50 [CI 1.10-2.05]; p = 0.01) and in women (OR = 1.45 [CI 1.02-2.07]; p = 0.038).

CONCLUSIONS

In coastal areas, which are believed to be rich in iodine, consuming non-iodized salt still led to lower UIC levels and a higher prevalence of iodine deficiency. The consumption of non-iodized salt and low UICs might be a risk factor for AITD, especially for women, which should be further confirmed by longitudinal studies.

Black Tea Source, Production, and Consumption: Assessment of Health Risks of Fluoride Intake in New Zealand

In countries with fluoridation of public water, it is imperative to determine other dietary sources of fluoride intake to reduce the public health risk of chronic exposure. New Zealand has one of the highest per capita consumption rates of black tea internationally and is one of the few countries to artificially fluoridate public water; yet no information is available to consumers on the fluoride levels in tea products. In this study, we determined the contribution of black tea as a source of dietary fluoride intake by measuring the fluoride content in 18 brands of commercially available products in New Zealand. Fluoride concentrations were measured by potentiometric method with a fluoride ion-selective electrode and the contribution of black tea to Adequate Intake (AI) and Tolerable Upper Intake Level (UL) was calculated for a range of consumption scenarios. We examined factors that influence the fluoride content in manufactured tea and tea infusions, as well as temporal changes in fluoride exposure from black tea. We review the international evidence regarding chronic fluoride intake and its association with chronic pain, arthritic disease, and musculoskeletal disorders and provide insights into possible association between fluoride intake and the high prevalence of these disorders in New Zealand.

Iodine Status of New Zealand Elderly Residents in Long-Term Residential Care

In response to the re-emergence of iodine deficiency in New Zealand, in 2009 the government mandated that all commercially made breads be fortified with iodized salt. There has been no evaluation of the impact of the program on iodine status of the elderly, despite this population group being vulnerable to iodine deficiency or excess. The aim of this study was to describe the iodine status of elderly New Zealanders in residential aged-care homes following the implementation of the bread fortification program. A cross-sectional survey was conducted, involving 309 residents (median age 85 years) from 16 aged-care homes throughout NZ. Information on socio-demographic, anthropometric, dietary and health characteristics were collected. Casual spot urine samples were analysed for urinary iodine concentration (UIC). Blood samples were analysed for serum thyroglobulin, thyroglobulin antibodies, and other biochemical indices. The median UIC (MUIC) of the residents was 72 μg/L, indicating mild iodine deficiency, and 29% had a UIC < 50 μg/L. Median thyroglobulin concentration was 18 ng/mL and 26% had elevated thyroglobulin concentration (>40 ng/mL), suggesting iodine insufficiency. Diuretic use was associated with lower MUIC (p = 0.043). Synthetic thyroxine use was associated with lower odds of having a UIC < 50 μg/L (OR 0.32, p = 0.030)) and lower median thyroglobulin (−15.2 ng/mL, p = 0.001), compared with untreated participants. Frailty was associated with elevated thyroglobulin (p = 0.029), whereas anemia was associated with lower thyroglobulin (p = 0.016). Iodine insufficiency persists in New Zealanders residing in residential aged-care homes despite increasing iodine intake from fortified bread. Research is required to establish optimal iodine intake and status in the elderly.

Iodine supplementation in pregnancy - is it time?

Iodine is essential for the synthesis of thyroid hormone and optimal foetal neurological development. Pregnant women living in borderline or moderate-severe iodine deficient areas are at particularly high risk of being iodine deficient, and this may have important clinical consequences, particularly for the neurocognitive development of the offspring. It is a substantial problem and many countries including the United Kingdom are mild-moderately iodine deficient. Although the detrimental effects of severe iodine deficiency are well recognized, the benefits of correcting mild-to-moderate iodine deficiency are unclear due to a lack of randomized controlled trials in this area. However, observational data increasingly indicate that there may be substantial health and economic benefits from correcting iodine deficiency in pregnancy. There is now a growing trend from learned societies that iodine supplementation should be utilized in pregnancy in countries with mild-to-moderate iodine deficiency. The dose of iodine supplement needs to reflect local iodine status and iodization policies and will need careful monitoring at the population level to ensure doses to prevent under/excess dosing which would undermine the potential benefits. National tailored guidance is therefore essential.

Adequate Iodine Status in New Zealand School Children Post-Fortification of Bread with Iodised Salt

Iodine deficiency re-emerged in New Zealand in the 1990s, prompting the mandatory fortification of bread with iodised salt from 2009. This study aimed to determine the iodine status of New Zealand children when the fortification of bread was well established. A cross-sectional survey of children aged 8–10 years was conducted in the cities of Auckland and Christchurch, New Zealand, from March to May 2015. Children provided a spot urine sample for the determination of urinary iodine concentration (UIC), a fingerpick blood sample for Thyroglobulin (Tg) concentration, and completed a questionnaire ascertaining socio-demographic information that also included an iodine-specific food frequency questionnaire (FFQ). The FFQ was used to estimate iodine intake from all main food sources including bread and iodised salt. The median UIC for all children (n = 415) was 116 μg/L (females 106 μg/L, males 131 μg/L) indicative of adequate iodine status according to the World Health Organisation (WHO, i.e., median UIC of 100–199 μg/L). The median Tg concentration was 8.7 μg/L, which was <10 μg/L confirming adequate iodine status. There was a significant difference in UIC by sex (p = 0.001) and ethnicity (p = 0.006). The mean iodine intake from the food-only model was 65 μg/day. Bread contributed 51% of total iodine intake in the food-only model, providing a mean iodine intake of 35 μg/day. The mean iodine intake from the food-plus-iodised salt model was 101 μg/day. In conclusion, the results of this study confirm that the iodine status in New Zealand school children is now adequate.

A low incidence of iodine-induced hyperthyroidism following administration of iodinated contrast in an iodine-deficient region

OBJECTIVE

There are limited data on the incidence of iodinated contrast-induced thyrotoxicosis, particularly in iodine-deficient regions. The aim of this study was to determine the incidence of iodinated contrast-induced thyrotoxicosis and to determine whether thyrotoxicosis was more common in patients ≥70 years compared to those <70 years of age.

DESIGN

A prospective study of adult patients undergoing an outpatient CT with iodinated contrast was performed.

MEASUREMENTS

Thyroid function tests (TFTs) and urine iodine measurements were performed prior to the scan. TFTs were repeated at 4- and 8-weeks postscan. Changes in TFTs from baseline were analysed.

RESULTS

A total of 102 patients were included in the final analysis. Overall, TSH levels dropped (P = 0·0002), and free T3 (FT3 ) levels increased (P = 0·04) between baseline and week 4 with normalization by week 8; however, these changes were not considered clinically significant. No significant differences in free T4 (FT4 ) occurred in the overall group (P = 0·82). There were no differences in TFTs between baseline and 4 or 8 weeks for those patients aged <70 compared to ≥70 years. Two patients developed new subnormal TSH values. Of these, one had a 90-mm follicular variant papillary thyroid carcinoma diagnosed while the other had a normal thyroid assessment and TSH spontaneously normalized by 12 weeks.

CONCLUSIONS

Only 2% of patients developed subclinical hyperthyroidism following a standard dose of iodinated contrast for CT investigations. Given the low incidence of iodine-induced thyrotoxicosis, there is no indication for routine pre- and post-CT thyroid function testing in our region.

CO-occurring exposure to perchlorate, nitrate and thiocyanate alters thyroid function in healthy pregnant women

BACKGROUND

Adequate maternal thyroid function during pregnancy is necessary for normal fetal brain development, making pregnancy a critical window of vulnerability to thyroid disrupting insults. Sodium/iodide symporter (NIS) inhibitors, namely perchlorate, nitrate, and thiocyanate, have been shown individually to competitively inhibit uptake of iodine by the thyroid. Several epidemiologic studies examined the association between these individual exposures and thyroid function. Few studies have examined the effect of this chemical mixture on thyroid function during pregnancy

OBJECTIVES

We examined the cross sectional association between urinary perchlorate, thiocyanate and nitrate concentrations and thyroid function among healthy pregnant women living in New York City using weighted quantile sum (WQS) regression.

METHODS

We measured thyroid stimulating hormone (TSH) and free thyroxine (FreeT4) in blood samples; perchlorate, thiocyanate, nitrate and iodide in urine samples collected from 284 pregnant women at 12 (±2.8) weeks gestation. We examined associations between urinary analyte concentrations and TSH or FreeT4 using linear regression or WQS adjusting for gestational age, urinary iodide and creatinine.

RESULTS

Individual analyte concentrations in urine were significantly correlated (Spearman's r 0.4-0.5, p<0.001). Linear regression analyses did not suggest associations between individual concentrations and thyroid function. The WQS revealed a significant positive association between the weighted sum of urinary concentrations of the three analytes and increased TSH. Perchlorate had the largest weight in the index, indicating the largest contribution to the WQS.

CONCLUSIONS

Co-exposure to perchlorate, nitrate and thiocyanate may alter maternal thyroid function, specifically TSH, during pregnancy.

The Relationship Between Iodine Intake and Serum Thyroglobulin in the General Population

The relationship is shown between a concentration of urinary iodine and serum thyroglobulin in population studies carried out on a general population that was randomly selected from the registry of the General Health Insurance Company (individuals aged 6-98 years, 1751 males, 2420 females). The individuals were divided into subgroups with a urinary iodine concentration of <50, 50-99, 100-199, 200-299 and ≥300 μg/l. The mean and median of thyroglobulin were calculated in these subgroups. Tg concentrations were dependent on gender (males<females), age (thyroglobulin increased with age) and statistically significant negative relationship was observed between thyroglobulin and urinary iodine in individuals with urinary iodine <300 μg/l and the age under 65 years. Upper nonparametric tolerance limits of thyroglobulin in relation to iodine intake were calculated in subgroup of normal individuals (n=1858, thyroglobulin, urinary iodine, thyrotropin and free thyroxine were within the normal reference range). Upper limits were dependent on gender and age. The total value of upper limits is 44 μg/l; for individuals aged 6-17 years it is 39.1 μg/l; 18-65 years = 51.4 μg/l and 66-98 years = 60.6 μg/l. In general, thyroglobulin serum concentrations higher than 40 μg/l should be an indicator for determining urinary iodine.

Examination of iodine status in the German population: an example for methodological pitfalls of the current approach of iodine status assessment

PURPOSE

Preliminary iodine concentration (UIC) measurements in spot urines of the representative German adult study DEGS indicated a severe worsening of iodine status compared to previous results in German children (KiGGS study). Therefore, we aimed to evaluate adult iodine status in detail and to investigate the impact of hydration status on UIC.

METHODS

UIC and creatinine concentrations were measured in 6978 spot urines from the German nationwide DEGS study (2008-2011). Twenty-four-hour iodine excretions (24-h UIE) were estimated by relating iodine/creatinine ratios to age- and sex-specific 24-h creatinine reference values. Urine osmolality was measured in two subsamples of spot urines (n = 100 each) to determine the impact of hydration status on UIC.

RESULTS

In DEGS, median UIC was 69 µg/L in men and 54 µg/L in women, lying clearly below the WHO cutoff for iodine sufficiency (100 µg/L). Estimated median 24-h UIE was 113 µg/day, accompanied by 32 % of DEGS adults, lying below the estimated average requirement (EAR) for iodine. Comparative analysis with the KiGGS data (>14,000 spot urines of children; median UIC 117 µg/L) revealed a comparable percentage <EAR (33 %). In two DEGS subsamples with significantly different UIC but similar median 24-h UIE, osmolality was twofold higher in the high- versus the low-UIC group.

CONCLUSION

Over 30 % of participants in the two German surveys had an estimated iodine intake less than the respective age-group-specific EAR. Our data strongly suggest that even in large surveys, hydration status can considerably interfere with the epidemiological iodine assessment parameter UIC. The present data can serve as an example how to evaluate population-based spot urine data on a 24-h basis, independent of hydration status.

Iodine nutritional status after the implementation of the new iodized salt concentration standard in Zhejiang Province, China

Background

Iodine deficiencies were prevalent in China until the introduction of universal salt iodization (USI) in 1995. In 2012, the standard salt iodine concentration was adjusted to 20-30 mg/kg. The success of USI for the control of iodine deficiency disorders requires monitoring its effect at a population level.

Methods

Two cross sectional surveys of a representative sample of children aged 8–10 years in Zhejiang Province were carried out in 2011 and 2013. Data on participants’ socio-demographic characteristics were collected from the children using a structured questionnaire. Spot urine samples were collected and delivered to local Center for Disease Control and Prevention laboratory for measuring urinary iodine concentration. In 2011, out of 420 selected children aged 8–10 years, 391 were recorded and provided urine samples. In 2013, out of 1560 selected children aged 8–10 years, 1556 were recorded and provided urine samples.

Results

The median urinary iodine concentration of subjects in the 2013 survey was 174.3 μg/L, significantly lower than that of 2011(p = 0.000). The median urinary iodine concentration of subjects living in urban and rural areas in the 2013 survey was 169.0 μg/L, and 186.1 μg/L respectively, significantly lower than that of 2011 only for subjects living in urban areas (p = 0.000). There were no significant differences for subjects living in rural areas in the survey in 2011 and in 2013 (p = 0.086).

Conclusions

At the time the new local iodization policy put forward, iodine nutrition was generally adequate in both urban and rural areas, suggesting that the new policy for adjusting the standard salt iodine concentration is effective. Our data also indicate that the reason people living in urban areas had a lower urinary iodine concentration than people in rural areas may be due to their preference for using non-iodized salt in the last 2 or 3 years. Maintaining USI at an appropriate level is an important part of preventing iodine deficiency disorders and should always be based on regular monitoring and comparison of urinary iodine concentration by province.

Thyroglobulin as a biomarker of iodine deficiency: a review

BACKGROUND

Thyroglobulin, produced exclusively by the thyroid gland, has been proposed to be a more sensitive biomarker of iodine status than thyrotropin or the thyroid hormones triiodothyronine and thyroxine. However, evidence on the usefulness of thyroglobulin (Tg) to assess iodine status has not been extensively reviewed, particularly in pregnant women and adults.

SUMMARY

An electronic literature search was conducted using the Cochrane CENTRAL, Web of Science, PubMed, and Medline to locate relevant studies on Tg as a biomarker of iodine status. Since urinary iodine concentration (UIC) is the recommended method to assess iodine status in populations, only studies that clearly reported both Tg and UIC were included. For the purpose of this review, a median Tg <13 μg/L and a median UIC ≥100 μg/L (UIC ≥150 μg/L for pregnant women) were used to indicate adequate iodine status. We excluded studies conducted in subjects with either known thyroid disease or those with thyroglobulin antibodies. The search strategy and selection criteria yielded 34 articles of which nine were intervention studies. The majority of studies (six of eight) reported that iodine-deficient pregnant women had a median Tg ≥13 μg/L. However, large observational studies of pregnant women, including women with adequate and inadequate iodine status, as well as well-designed intervention trials that include both Tg and UIC, are needed. In adults, the results were equivocal because iodine-deficient adults were reported to have median Tg values of either <13 or ≥13 μg/L. Only studies in school-aged children showed that iodine-sufficient children typically had a median Tg <13 μg/L. Some of the inconsistent results may be partially explained by the use of different methodological assays and failure to assess assay accuracy using a certified reference material.

CONCLUSIONS

These data suggest that Tg does hold promise as a biomarker of iodine deficiency. However, it is associated with limitations. A median Tg cutoff of 13 μg/L warrants further investigation, particularly in adults or pregnant women, as there is a lack of both observational and intervention studies in these groups.

Mandatory fortification of bread with iodised salt modestly improves iodine status in schoolchildren

Iodine deficiency has re-emerged in many parts of the world including the UK, Australia and New Zealand (NZ). In 2009, the NZ government introduced the mandatory fortification of bread with iodised salt as a strategy to improve iodine intakes. The aim of the present study was to assess the impact of fortification on the iodine status of NZ schoolchildren. A school-based cluster survey was used to randomly select schools from two NZ cities. Children aged 8–10 years were administered a general questionnaire, and asked to provide a casual urine and finger-prick blood sample. The median urinary iodine concentration (UIC) of the children (n147) was 113 μg/l, which falls between 100 and 199 μg/l indicating adequate iodine status; 12 % of children had a UIC < 50 μg/l and 39 % had a UIC < 100 μg/l. The median serum thyroxine concentration was 115 nmol/l. The median serum thyroglobulin (Tg) concentration was 10·8 μg/l and falls in the 10·0–19·9 μg/l range indicative of mild iodine deficiency, suggesting that these children still had enlarged thyroid glands. When compared with the median UIC of 68 μg/l reported in the 2002 NZ Children's Nutrition Survey, the UIC of children in the present study had increased, which is probably caused by the addition of iodised salt to bread. However, the elevated concentration of Tg in these children suggests that the increase in UIC is not sufficient to ensure that thyroid volume has normalised. The fortification of other staple foods, in addition to bread, should be considered to ensure good iodine status in NZ children.