Swiss pilot study of individual seasonal fluctuations of urinary iodine concentration over two years: is age-dependency linked to the major source of dietary iodine?

Salivary iodine concentration in pregnant women and its association with iodine status and thyroid function

PURPOSE

There have been no reports on the application of salivary iodine concentration (SIC) in evaluating iodine nutrition in pregnant women. This study aimed to clarify the relationship between SIC and indicators of iodine nutritional status and thyroid function during pregnancy, to investigate whether salivary iodine can be applied to the evaluation of iodine nutritional status in pregnant women, and to provide a reference basis for establishing a normal range of salivary iodine values during pregnancy.

METHODS

Pregnant women were enrolled in the Department of Obstetrics, the people's hospital of Yuncheng Country, Shandong Province, from July 2021 to December 2022, using random cluster sampling. Saliva, urine, and blood samples were collected from pregnant women to assess iodine nutritional status, and venous blood was collected to determine thyroid function.

RESULTS

A total of 609 pregnant women were included in this study. The median spot urinary iodine concentration (SUIC) was 261 μg/L. The median SIC was 297 μg/L. SIC was positively correlated with SUIC (r = 0.46, P < 0.0001), 24-h UIC (r = 0.30, P < 0.0001), 24-h urinary iodine excretion (24-h UIE) (r = 0.41, P < 0.0001), and estimated iodine intake (EII) (r = 0.52, P < 0.0001). After adjusting for confounders, there was a weak correlation between SIC and serum total iodine and serum non-protein-bound iodine (P = 0.02, P = 0.04, respectively). Pregnant women with a SIC < 176 μg/L had a higher risk of insufficient iodine status (OR = 2.07, 95% CI 1.35-3.19) and thyroid dysfunction (OR = 2.71, 95% CI 1.18-6.21) compared to those with higher SIC. Those having SIC > 529 μg/L were more likely to have excessive iodine status (OR = 2.82, 95% CI 1.81-4.38) and thyroid dysfunction (OR = 3.04, 95% CI 1.36-6.78) than those with lower SIC values.

CONCLUSION

SIC is associated with urinary iodine concentration and thyroid function in pregnant women. SIC < 176 μg/L was associated with an increased risk for iodine deficiency and hypothyroxinemia, while SIC > 529 μg/L was related to excess and thyrotoxicosis. SIC can be used as a reference indicator for evaluating the iodine nutrition status of pregnant women, but it needs further investigation and verification.

TRIAL REGISTRATION

NCT04492657(Aug 9, 2022).

Comparison of body iodine pool assessment methods before radioiodine therapy

INTRODUCTION AND OBJECTIVES

Radioactive iodine therapy (RAIT) is recommended to reduce the risk of recurrence and metastasis in patients with intermediate-high risk differentiated thyroid cancer (DTC). In preparation for RAIT, stimulation of thyroid-stimulating hormone and reduction of body iodine pool are important for treatment success. For this purpose, patients are asked to reduce their iodine intake before RAIT, and the body iodine pool can be evaluated by measuring iodine excretion in urine before treatment. The aim of our study is to compare the methods used to measure the body iodine pool in the evaluation of the restricted iodine diet (RID) effectiveness applied in the RAIT preparation.

PATIENTS AND METHODS

Eighty DTC patients discontinued levothyroxine three weeks before RAIT and followed up with a RID two weeks before treatment. After two weeks of RID, all patients collected their 24-h urine the day before the RAIT date. Patients completed 24-h urine samples on the morning of the RAIT date and also provided a spot urine sample. The estimated 24-h creatinine excretion of the patients was calculated. Estimated 24-h urinary iodine excretion (UIE) was calculated using the spot urine iodine/creatinine (I/C) ratio of the patients. 24-h UIE, iodine concentration in spot urine, I/C ratios in spot urine and estimated 24-h UIE of the patients were analyzed by comparing with each other.

RESULTS

In 99% of the patients, RID efficiency was sufficient according to 24-h UIE before RAIT. The mean 24-h UIE was 48.81 micrograms/day (mcg/day) in 24-h urine samples taken from the patients to evaluate the body iodine pool. The patients' iodine concentrations in spot urine, I/C ratios in spot urine, and estimated 24-h UIE were all statistically significantly lower than actual 24-h UIE, which was the reference method (p: 0.026 vs <0.001 vs 0.041). Moderate positive correlation between 24-h UIE and iodine concentration in spot urine (r: 0.440), I/C ratio in spot urine (r: 0.493), and estimated 24-h UIE (r: 0.560) found. The strongest correlation was obtained with the estimated 24-h UIE.

CONCLUSION

The estimated 24-h UIE obtained by using the I/C ratio in spot urine can be used practically and safely as an alternative to UIE in 24-h urine, which is the gold standard method for evaluating body iodine pool.

Urinary iodine excretion and optimal time point for sampling when estimating 24-h urinary iodine

Iodine deficiency may cause thyroid dysfunction. The iodine intake in a population is measured by urinary iodine concentration (UIC) in spot samples or 24-h urinary iodine excretion (24UIE). 24UIE is considered the gold standard and may be estimated using an equation including UIC, urinary creatinine concentration, sex and age (e24UIE). The aims of this study were to evaluate the preferable timing of UIC when using this equation and assess the variability of UIE. Sixty healthy non-smoking women (n 31) and men (n 29) were included in Gothenburg, Sweden. Twelve urine samples were collected at six fixed times on two separate days. Variability was calculated for UIC, 24UIE, e24UIE, iodine excretion per hour (iHr) and UIC adjusted for creatinine and specific gravity. Median 24UIE was 156 µg/24 h and the median UIC (all spot samples) was 104 µg/l. UIC (P < 0·001), 24UIE (P = 0·001) and e24UIE (P < 0·001) were significantly higher in men. e24UIE was relatively similar to 24UIE. However, when e24UIE was calculated from UIC in the first void, it was about 15 % lower than 24UIE (P < 0·001). iHr was lowest in the morning and highest in the afternoon. Median iHr was higher in men (7·4 v. 5·3 µg/h, P < 0·001). The variability of UIE was higher within individuals than between individuals. This study suggests that most time points for estimation of individual 24UIE are appropriate, but they should preferably not be collected in the first void.

Iodine Deficiency and Iodine Prophylaxis: An Overview and Update

The thyroid gland requires iodine to synthesize thyroid hormones, and iodine deficiency results in the inadequate production of thyroxine and related thyroid, metabolic, developmental, and reproductive disorders. Iodine requirements are higher in infants, children, and during pregnancy and lactation than in adult men and non-pregnant women. Iodine is available in a wide range of foods and water and is susceptible to almost complete gastric and duodenal absorption as an iodide ion. A healthy diet usually provides a daily iodine consumption not exceeding 50% of the recommended intake. Iodine supplementation is usually necessary to prevent iodine deficiency disorders (IDDs), especially in endemic areas. The community-based strategy of iodine fortification in salt has eradicated IDDs, such as endemic goiter and cretinism, in countries providing adequate measures of iodine prophylaxis over several decades in the 20th century. Iodized salt is the cornerstone of iodine prophylaxis in endemic areas, and the continuous monitoring of community iodine intake and its related clinical outcomes is essential. Despite the relevant improvement in clinical outcomes, subclinical iodine deficiency persists even in Western Europe, especially among girls and women, being an issue in certain physiological conditions, such as pregnancy and lactation, and in people consuming unbalanced vegetable-based or salt-restricted diets. Detailed strategies to implement iodine intake (supplementation) could be considered for specific population groups when iodized salt alone is insufficient to provide adequate requirements.

Variations in Breast Milk Iodine Concentration over 24 h among Lactating Women in Northern China

BACKGROUND

Adequate breast milk iodine concentration (BMIC) is essential for the growth and cognitive development of exclusively breastfed infants; however, data on variations in BMIC over 24 h are limited.

OBJECTIVE

We aimed to explore in lactating women the variation in 24-h BMIC.

METHODS

Thirty pairs of mothers and breastfed infants aged 0-6 mo were recruited from the cities of Tianjin and Luoyang, China. A 3-d 24-h dietary record, including salt intake, was performed to assess the dietary iodine intake of lactating women. Breast milk samples before and after each feeding for 24 h and 24-h urine samples were collected from the women for 3 d to estimate iodine excretion. A multivariate linear regression model was used to analyze the factors influencing BMIC. A total of 2658 breast milk samples and 90 24-h urine samples were collected.

RESULTS

The median BMIC and 24-h urine iodine concentration (UIC) of lactating women for a mean of 3.6 ± 1.48 mo were 158 μg/L and 137 μg/L, respectively. The interindividual variability of BMIC (35.1%) was higher than that observed within individuals (11.8%). The variation in BMIC showed a "V" shaped curve over 24 h. The median BMIC at 08:00-12:00 (137 μg/L) was significantly lower than that at 20:00-24:00 (163 μg/L) and 00:00-04:00 (164 μg/L). A progressively increasing curve was obtained for BMIC until it peaked at 20:00 and plateaued at a higher concentration from 20:00 to 04:00 than at 08:00-12:00 (all P < 0.05). BMIC was associated with dietary iodine intake (β: 0.366; 95% CI: 0.004, 0.018) and infant age (β: -0.432; 95% CI: -1.07, -0.322).

CONCLUSIONS

Our study shows that the BMIC presents a "V" shaped curve over 24 h. We recommend that breast milk samples be collected between 08:00 and 12:00 for evaluation of the iodine status of lactating women.

Iodine intake in healthy Japanese aged from 6 to 70 years residing in the same district

Iodine is an essential component of thyroid hormones and a dietary micronutrient for humans, and adequate iodine intake is necessary to maintain thyroid function. A population's iodine intake and nutritional status are assessed based on urinary iodine excretion. There are few studies on iodine nutritional status for all age groups residing in the same area in Japan. Between 2010 and 2017, a total of 769 healthy subjects aged 6.4-73 years in three sites in Yokohama City, were enrolled in the survey. The urinary iodine concentration (UIC), iodine to creatinine (Cr) ratio (UI/Cr) and estimated 24-h urinary iodine excretion (UIE) in single spot urine samples were measured, and habitual dietary iodine intake was assessed by food frequency questionnaires. The estimated 24-h UIE was calculated using individual predicted 24-h creatinine excretion by the validated equations developed for healthy Japanese children and adults which vary by age, gender and anthropometry. The median UIC for all participants was 219 μg/L, suggesting adequate iodine intake for this population. There was an increasing trend in median UI/Cr and estimated 24-h UIE by age. A significant correlation between UIC and UI/Cr (r = 0.6378), UIC and estimated 24-h UIE (r = 0.6804), and UI/Cr and estimated 24-h UIE (r = 0.5756) were observed. These estimates can be feasible, convenient and alternative methods to 24-h urine collection in order to assess iodine status in some populations such as ethnically or racially homogeneous and well-nourished people. Additional studies are required to validate these findings.

Seasonal effects on urinary iodine concentrations in women of reproductive age: An observational study in Tanzania and South Africa

BACKGROUND

Iodine intake in populations is usually assessed by measuring urinary iodine concentrations (UICs) in spot samples. Hot climate conditions may reduce urine volume, thus leading to overestimations of UIC and thereby masking inadequate iodine intake.

OBJECTIVES

We investigated the effects of season on UICs in 2 populations exposed to high-temperature climates.

METHODS

In this observational study, we examined women (18-49 years) in Tanzania (ncold = 206; nhot = 179) and South Africa (ncold = 157; nhot = 126) during cold and hot seasons. From each woman in both seasons, we obtained two 24-hour urine collections and 2 spot urine samples, as well as salt, water, and cow's milk samples. We measured the urine volume, UIC, and urinary creatinine concentration (UCC). The 24-hour urinary iodine excretion (UIE) was calculated and used to estimate the iodine intake. We used linear mixed-effects models to test for differences between seasons.

RESULTS

In Tanzanian women, we observed no seasonal effect on the urine volume, 24-hour UIE, 24-hour UIC, spot UIC, spot UIC:UCC ratio, or salt iodine concentration. In South African women, the median 24-hour urine volume was 1.40 L (IQR, 0.96-2.05 L) in the winter and 15% lower in the summer (P < 0.001). The median 24-hour UIE was 184 µg/day (IQR, 109-267 µg/day) in the winter and 34% lower in the summer (P < 0.001), indicating a lower iodine intake. As a result, UICs did not significantly differ between seasons in 24-hour collections and spot samples, whereas the spot UIC:UCC ratio differed by 21% (P < 0.001) and reflected the lower iodine intake. In both study populations, the within- and between-person variabilities in urine volume, 24-hour UICs, and spot UICs were higher than the variability between seasons.

CONCLUSIONS

Spot UIC may slightly overestimate the iodine intake in hot temperatures due to concentrated urine, and methods to correct for urine volume may be considered. Local seasonal differences in iodine intakes may also occur in some populations. This trial was registered at http://www.clinicaltrials.gov as NCT03215680.

Determinants of placental iodine concentrations in a mild-to-moderate iodine-deficient population: an ENVIRONAGE cohort study

Background

Iodine is an essential trace element for the production of thyroid hormones, and plays a key role during the gestational period for optimal foetal growth and (neuro-)development. To this day, iodine deficiency remains a global burden. Previous studies indicate that the placenta can store iodine in a concentration-dependent manner and serve as a long-term storage supply, but studies on the determinants of long-term placental iodine load are limited.

Methods

The placental iodine concentrations were determined for 462 mother-neonate pairs from the ENVIRONAGE birth cohort (Limburg, Belgium). Sociodemographic and clinical variables were obtained from questionnaires and medical files. Determinants of placental iodine concentration were identified using stepwise multiple regression procedures (p value < 0.15). The biological significance of our findings was investigated by measuring the plasma thyroid hormones in maternal and cord blood of 378 participants.

Results

A higher pre-pregnancy BMI, higher gestational weight gain, and alcohol consumption during pregnancy were linked with lower placental iodine storage. Multi-vitamin supplementation during pregnancy and longer gestation were associated with higher levels of placental iodine. Children born during the winter period had on average higher placental iodine levels. Besides, we found a significant positive time trend for placental iodine load over the study period 2013 to 2017. Lastly, we observed positive associations of both the maternal and cord plasma thyroxine concentrations with placental iodine load, emphasizing their biological link.

Conclusions

This study identified some determinants likely presenting a risk of reduced iodine storage during the gestational period of life. Future studies should elucidate the effects of lower placental iodine load on neonatal health, and health later in life.

Intra-individual and inter-individual variations in iodine intake and excretion in adult women: implications for sampling

Iodine intake and excretion vary widely; however, these variations remain a large source of geometric uncertainty. The present study aims to analyse variations in iodine intake and excretion and provide implications for sampling in studies of individuals or populations. Twenty-four healthy women volunteers were recruited for a 12-d sampling period during the 4-week experiment. The duplicate-portion technique was used to measure iodine intake, while 24-h urine was collected to estimate iodine excretion. The mean intra-individual variations in iodine intake, 24-h UIE (24-h urinary iodine excretion) and 24-h UIC (24-h urinary iodine concentration) were 63, 48 and 55 %, respectively, while the inter-individual variations for these parameters were 14, 24 and 32 %, respectively. For 95 % confidence, approximately 500 diet samples or 24-h urine samples should be taken from an individual to estimate their iodine intake or iodine status at a precision range of ±5%. Obtaining a precision range of ±5% in a population would require twenty-five diet samples or 150 24-h urine samples. The intra-individual variations in iodine intake and excretion were higher than the inter-individual variations, which indicates the need for more samples in a study on individual participants.

Dietary Relationship with 24 h Urinary Iodine Concentrations of Young Adults in the Mountain West Region of the United States

Background: Iodine deficiency is not seen as a public health concern in the US. However certain subpopulations may be vulnerable due to inadequate dietary sources. The purpose of the present study was to determine the dietary habits that influence iodine status in young adult men and women, and to evaluate the relationship between iodine status and thyroid function. Methods: 111 participants (31.6 ± 0.8 years, 173.2 ± 1.0 cm, 74.9 ± 1.7 kg) provided 24 h urine samples and completed an iodine-specific Food Frequency Questionnaire (FFQ) for assessment of urinary iodine content (UIC) as a marker of iodine status and habitual iodine intake, respectively. Serum Thyroid Stimulating Hormone (TSH) concentration was evaluated as a marker of thyroid function. Spearman correlational and regression analysis were performed to analyze the associations between iodine intake and iodine status, and iodine status and thyroid function. Results: 50.4% of participants had a 24 h UIC < 100 µg/L). Dairy (r = 0.391, p < 0.000) and egg intake (r = 0.192, p = 0.044) were the best predictors of UIC, accounting for 19.7% of the variance (p ≤ 0.0001). There was a significant correlation between UIC and serum TSH (r = 0.194, p < 0.05) but TSH did not vary by iodine status category (F = 1.087, p = 0.372). Discussion: Total dairy and egg intake were the primary predictors of estimated iodine intake, as well as UIC. Iodized salt use was not a significant predictor, raising questions about the reliability of iodized salt recall. These data will be useful in directing public health and clinical assessment efforts in the US and other countries.

Iodine contents in conventional ultra-high temperature (UHT) processed cow milk: Changes over the year and regional differences. Implications for epidemiological studies on iodine nutritional status

BACKGROUND AND OBJECTIVES

Ultra-high temperature (UHT) processed cow milk is the milk most commonly consumed in Southwest Europe. The study objectives were: 1) to describe the pattern followed by iodine concentration (IC) in conventional UHT milk over the year, and 2) to find out any differences in IC in this type of milk depending on its geographical origin.

MATERIAL AND METHODS

Bricks of conventional UHT cow milk of commercial brands available in food stores in Vitoria-Gasteiz (Araba/Álava), Basque Country (Spain) were bought for 12 consecutive months, and their ICs were measured using high performance liquid chromatography.

RESULTS

Median (P₂₅-P₇₅) IC in UHT milk (n=489) was 190 (159-235)μg/L. IC in milk showed great changes over the year, reaching peak values between January and May (241 [201-272]μg/L), and minimal levels between July and November (162 [134-185]μg/L) (P<.0001). The IC of milk packed in Germany was significantly lower than that of milks packed in Spain and France, 119 (106-156)μg/L versus 189 (159-229)μg/L and 205 (176-243)μg/L respectively (P<.0001).

CONCLUSIONS

Conventional UHT cow milk is a very important nutritional source of iodine, but its IC is highly variable. Knowledge of the pattern followed by IC in milk over the year is of great interest for planning epidemiological studies on iodine nutritional status in schoolchildren and for interpretation of their results.

The assessment of iodine status - populations, individuals and limitations

Iodine deficiency is a significant global health concern, and the single greatest cause of preventable cognitive impairment. It is also a growing public health concern in the UK particularly among pregnant women. Biomarkers such as urinary iodine concentration have clear utility in epidemiological studies to investigate population-level iodine status, but determination of iodine status in individuals is much more problematic with current assays. This article reviews the available biomarkers of iodine status and their relative utility at the level of both populations and individuals for the investigation of iodine deficiency and iodine excess.

24-Hour Urine Samples Are More Reproducible Than Spot Urine Samples for Evaluation of Iodine Status in School-Age Children

BACKGROUND

Variation in different urinary measurements for evaluation of iodine status is of concern to clinicians and researchers.

OBJECTIVE

This study evaluated variations between urine iodine concentration (UIC), spot and 24-h urine sample creatinine concentrations, and 24-h urine iodine excretion (24-h UIE) in repeated samples from school-age children.

METHODS

Urine samples (24 h and morning spot) were collected on 2 occasions from 981 children in Ningjin and Lingxian counties, China. Samples from Ningjin were collected in October and November 2013, and samples from Lingxian were collected in April and May 2014. Morning spot urine iodine concentration (MUIC), morning spot urine creatinine, 24-h UIC, and 24-h urine creatinine were measured in all samples. The 24-h UIE was calculated by multiplying the 24-h UIC by the 24-h urine volume.

RESULTS

In Ningjin County, the 24-h UIC and 24-h UIE did not differ between repeated collections [192 and 172 μg/L, respectively, for 24-h UIC (P = 0.08); 123 and 120 μg/L, respectively, for 24-h UIE (P = 0.56)], whereas the MUIC was lower in November 2013 than in October 2013 (170 and 190 μg/L, respectively; P = 0.034). In Lingxian County, no significant differences were observed in 24-h UIC between the repeated collections (230 and 218 μg/L, respectively; P = 0.79), whereas the 24-h UIE and MUIC were higher in the samples collected in May 2014 than in April 2014 [161 and 155 μg/L, respectively, for 24-h UIE (P = 0.002); 244 and 203 μg/L, respectively, for MUIC (P < 0.001)]. When data from both counties were combined, no difference was observed between repeated 24-h UIC (214 compared with 196 μg/L; P = 0.17) and 24-h UIE (143 compared with 143 μg/d; P = 0.06), but MUICs were lower in the first collection than in the second collection (199 and 207 μg/L, respectively; P = 0.002). The κ values were >0.4 for 24-h UIC and mean UIE, whereas relatively low κ values were observed for MUIC and mean UIE.

CONCLUSION

The 24-h UIC was more accurate and reproducible than the MUIC in evaluating iodine status in a large-scale population study of school-age children.

Iodine deficiency during pregnancy: a national cross-sectional survey in Latvia

Objective

Low iodine intake during pregnancy may cause thyroid dysfunction, which results in inadequate fetal brain development. In the absence of a universal salt iodization programme, we conducted a nationwide survey of iodine deficiency in pregnant women in Latvia.

Design

A countrywide twenty-cluster survey, with at least twenty women per cluster. Participants completed a questionnaire on dietary habits concerning iodine intake (n 739). Thyroid function (thyroid-stimulating hormone, free thyroxine and thyroperoxidase antibodies) was measured (n 550). Urinary iodine was measured using the ammonium persulfate method (n 696).

Setting

The survey was performed in all regions of Latvia during the spring and autumn seasons in 2013.

Subjects

Pregnant women (n 829).

Results

The median creatinine (Cr)-standardized urinary iodine concentration (UIC) was 80·8 (interquartile range (IQR) 46·1–130·6) µg/g Cr or 69·4 (IQR 53·9–92·6) µg/l during pregnancy, and 81 % of pregnant women had UIC levels below the WHO recommended range of 150–250 µg/g Cr. The UIC was lowest during the first trimester of pregnancy, 56·0 (IQR 36·4–100·6) µg/g Cr, reaching higher concentrations of 87·5 (IQR 46·4–141·7) µg/g Cr and 86·9 (IQR 53·8–140·6) µg/g Cr in the second and third trimesters, respectively. Women taking supplements containing ≥150 µg iodine (6·8 % of respondents) had non-significantly higher UIC than did women without supplementation (96·2 v. 80·3 µg/g Cr, respectively, P=NS). Thyroperoxidase antibody concentration did not correlate significantly with UIC: Spearman’s ρ=−0·012, P=0·78.

Conclusions

The median UIC indicates iodine deficiency in pregnant women in Latvia. Iodine supplementation (150 µg daily) and regular UIC monitoring should be suggested to overcome iodine deficiency and to reach the recommended levels without inducing autoimmune processes.

[Iodine concentration in ultra-high temperature pasteurized cow's milk. Applications in clinical practice and in community nutrition]

BACKGROUND AND OBJECTIVE

Changes to dairy cow feeding have made milk a very important food source of iodine in several European countries and in USA. We aimed to measure the iodine content in ultra-high temperature (UHT) milk, the most widely consumed milk in Spain and in the south-west of Europe.

MATERIAL AND METHODS

Every month, throughout 2008, UHT milk samples of commercial brands available in Vitoria-Gasteiz (Basque Country, Spain) were collected and their iodine content was determined using high-performance liquid chromatography, according to official method 992.22 of the Association of Official Analytical Chemists International.

RESULTS

The average (SD) iodide content and median (P25-P75) of standard UHT milk samples (n=489) were 197.6 (58.1) and 190 (159-235) μg/L, respectively. There were no significant differences between the iodide content in whole, semi-skimmed and skimmed milk (P=.219). The average iodide concentration and median in organic UHT milk (n=12) were 56.4 (8.6) and 55 (50.5-61.5) μg/L, figures that are much lower than those found in standard milk (P<.0001).

CONCLUSIONS

Standard UHT milk available in our food-retailing outlets constitutes a very important source of iodine. One glass of standard UHT milk (200-250mL) provides an average amount of 50μg of iodine. This amount represents around 50% of the iodine intake recommended during childhood or 20% of the iodine intake recommended for pregnant and lactating women.

Prevalence of iodine inadequacy in Switzerland assessed by the estimated average requirement cut-point method in relation to the impact of iodized salt

OBJECTIVE

To assess the iodine status of Swiss population groups and to evaluate the influence of iodized salt as a vector for iodine fortification.

DESIGN

The relationship between 24 h urinary iodine and Na excretions was assessed in the general population after correcting for confounders. Single-day intakes were estimated assuming that 92 % of dietary iodine was excreted in 24 h urine. Usual intake distributions were derived for male and female population groups after adjustment for within-subject variability. The estimated average requirement (EAR) cut-point method was applied as guidance to assess the inadequacy of the iodine supply.

SETTING

Public health strategies to reduce the dietary salt intake in the general population may affect its iodine supply.

SUBJECTS

The study population (1481 volunteers, aged ≥15 years) was randomly selected from three different linguistic regions of Switzerland.

RESULTS

The 24 h urine samples from 1420 participants were determined to be properly collected. Mean iodine intakes obtained for men (n 705) and women (n 715) were 179 (sd 68.1) µg/d and 138 (sd 57.8) µg/d, respectively. Urinary Na and Ca, and BMI were significantly and positively associated with higher iodine intake, as were men and non-smokers. Fifty-four per cent of the total iodine intake originated from iodized salt. The prevalence of inadequate iodine intake as estimated by the EAR cut-point method was 2 % for men and 14 % for women.

CONCLUSIONS

The estimated prevalence of inadequate iodine intake was within the optimal target range of 2-3 % for men, but not for women.

The iodized salt programme in Bangalore, India provides adequate iodine intakes in pregnant women and more-than-adequate iodine intakes in their children

Objective

To compare the iodine status of pregnant women and their children who were sharing all meals in Bangalore, India.

Design

A cross-sectional study evaluating demographic characteristics, household salt iodine concentration and salt usage patterns, urinary iodine concentrations (UIC) in women and children, and maternal thyroid volume (ultrasound).

Setting

Antenatal clinic of an urban tertiary-care hospital, which serves a low-income population.

Subjects

Healthy pregnant women in all trimesters, aged 18–35 years, who had healthy children aged 3–15 years.

Results

Median (range) iodine concentrations of household powdered and crystal salt were 55·9 (17·2–65·9) ppm and 18·9 (2·2–68·2) ppm, respectively. The contribution of iodine-containing supplements and multi-micronutrient powders to iodine intake in the families was negligible. Adequately iodized salt, together with small amounts of iodine in local foods, were providing adequate iodine during pregnancy: (i) the overall median (range) UIC in women was 172 (5–1024) µg/l; (ii) the median UIC was >150 µg/l in all trimesters; and (iii) thyroid size was not significantly different across trimesters. At the same time, the median (range) UIC in children was 220 (10–782) µg/l, indicating more-than-adequate iodine intake at this age. Median UIC was significantly higher in children than in their mothers (P=0·008).

Conclusions

In this selected urban population of southern India, the iodized salt programme provides adequate iodine to women throughout pregnancy, at the expense of higher iodine intake in their children. Thus we suggest that the current cut-off for median UIC in children indicating more-than-adequate intake, recommended by the WHO/UNICEF/International Council for the Control of Iodine Deficiency Disorders may, need to be reconsidered.

Variations of urinary iodine during the first trimester of pregnancy in an iodine-replete area. Comparison with non-pregnant women

OBJECTIVE

To assess variations of urinary iodine concentration (UIC) during a 4-week period among pregnant and non-pregnant women in an iodine-replete area.

DESIGN

Pregnant (in their first trimester of pregnancy) and non-pregnant women referred to two maternity hospitals in Tehran were consecutively recruited from September 2005 to March 2006. Urine samples (5-10 mL) were collected on an every-other-day basis for 4 weeks (i.e., 12 samples for each individual). UIC was determined using a modified Sandell-Kolthoff method.

RESULTS

Thirty-six pregnant and 32 non-pregnant women completed the study. Mean±SD age of pregnant women was 27.4±6.4 and of non-pregnant women 27.6±4.5 years (P=0.897). Mean±SD gestational age was 11±3.3 weeks in pregnant participants. Median UIC of <100, 100-149, 150-249, and ≥250 µg/L was present in 19.4, 25, 30.6, and 25% of pregnant, 15.6, 37.5, 34.4, and 12.5% of non-pregnant, and 17.6, 30.9, 32.4, and 19.1% of total individuals, respectively. Median UIC values of samples numbers 1 to 12 were not significantly different either in pregnant (P=0.591) or in non-pregnant subjects (P=0.745). Except for sample number 11, median UIC was not significantly different between pregnant versus non-pregnant women (P values >0.05). Mean SD values for UIC in samples numbers 1 to 12 in pregnant women was 138.4 (24.1-404) and in non-pregnant women 118 (29.5-272.4) µg/L (P=0.286).

CONCLUSION

There was a wide intrapersonal variation in UIC values among pregnant and non-pregnant women residing in an iodine-replete area, supporting the notion that casual UIC would not reflect the iodine status of the individual.

Iodine deficiency among Belgian pregnant women not fully corrected by iodine-containing multivitamins: a national cross-sectional survey

Low iodine intake during pregnancy may cause thyroid dysfunction in pregnant women and their newborn. In the present study, iodine status among a nation-wide representative sample of Belgian pregnant women in the first and third trimester of pregnancy was determined, and determinants of iodine status were assessed 1 year after the introduction of bread fortified with iodised salt. The women were selected according to a multistage proportionate-to-size sampling design. Urine samples were collected and a general questionnaire was completed face to face with the study nurse. The median urinary iodine concentration (UIC) among pregnant women (n1311) was 124·1 μg/l and 122·6 μg/g creatinine when corrected for urinary creatinine. The median UIC in the first trimester (118·3 μg/l) was significantly lower than that in the third trimester (131·0 μg/l) but significantly higher than among non-pregnant women (84·8 μg/l). Iodine-containing supplement intake was reported by 60·8 % of the women and 57·4 % of the women took this supplement daily. The risk of iodine deficiency was significantly higher in younger women, in women not taking iodine-containing supplements, with low consumption of milk and dairy drinks and during autumn. Women with a higher BMI had a higher risk of iodine deficiency but the risk was lower in women who reported alcohol consumption. The median UIC during pregnancy indicates iodine deficiency in Belgium and some women are at a higher risk of deficiency. The current low iodine intake in women of childbearing age precludes the correction of iodine deficiency in pregnant women supplemented with multivitamins containing 150 μg iodine as recommended.

Changes in iodine nutrition status in schoolchildren from the Basque Country

BACKGROUND

An epidemiologic survey showed in 1992 iodine deficiency and endemic goiter in schoolchildren from the Basque Country.

OBJECTIVES

(1) To determine the percentage of homes of schoolchildren where iodized salt (IS) is used; (2) to assess iodine nutrition status in schoolchildren and to compare the data collected to those available from previous epidemiological studies.

DESIGN AND METHODS

A cross-sectional study in 720 randomly selected schoolchildren. Urinary iodine concentration (UIC) was measured using high-performance liquid chromatography(HPLC) with electrochemical detection.

RESULTS

IS was used at 53.0% of the homes (95% confidence interval [CI], 49.2-56.7%). Median UIC has increased by 226%, from 65 μg/L in 1992 to 147 μg/L (percentile [P], P(25), 99 μg/L; P(75), 233 μg/L) today. Both schoolchildren consuming IS and those using unfortified salt at their homes had UICs corresponding to adequate iodine intakes (165 and 132 μg/L respectively). UICs experienced great seasonal fluctuations, being 55% higher during the November-February period than in June-September period (191 μg/L vs 123 μg/L; p<0.001)

CONCLUSIONS

Schoolchildren from the Basque Country have normalized their iodine nutrition status. The strong seasonal pattern of UICs suggests that consumption of milk and iodine-rich dairy products coming from cows feed iodized fodder is one of the most significant factors involved in the increase in iodine intake since 1992.

Ten repeat collections for urinary iodine from spot samples or 24-hour samples are needed to reliably estimate individual iodine status in women

Although the median urinary iodine concentration (UIC) is a good indicator of iodine status in populations, there is no established biomarker for individual iodine status. If the UIC were to be used to assess individuals, it is unclear how many repeat urine collections would be needed and if the collections should be spot samples or 24-h samples. In a prospective, longitudinal, 15-mo study, healthy Swiss women (n = 22) aged 52-77 y collected repeated 24-h urine samples (total n = 341) and corresponding fasting, second-void, morning spot urine samples (n = 177). From the UIC in spot samples, 24-h urinary iodine excretion (UIE) was extrapolated based on the age- and sex-adjusted iodine:creatinine ratio. Measured UIE in 24-h samples, estimated 24-h UIE, and UIC in spot samples were (geometric mean ± SD) 103 ± 28 μg/24 h, 86 ± 33 μg/24 h, and 68 ± 28 μg/L, respectively, with no seasonal differences. Intra-individual variation (mean CV) was comparable for measured UIE (32%) and estimated UIE (33%). The CV tended to be higher for the spot UIC (38%) than for the estimated 24-h UIE (33%) (P = 0.12). In this population, 10 spot urine samples or 24-h urine samples were needed to assess individual iodine status with 20% precision. Spot samples would likely be preferable because of their ease of collection. However, the large number of repeated urine samples needed to estimate individual iodine status is a major limitation and emphasizes the need for further investigation of more practical biomarkers of individual iodine status.

Does a small difference in iodine status among children in two regions of Belgium translate into a different prevalence of thyroid nodular diseases in adults?

PURPOSE

To explore whether there are regional differences in iodine status and in prevalence of thyroid diseases in the two main regions of Belgium.

METHODS

A national survey of iodine status among children was performed in 1998. The raw data of this survey were reanalyzed to explore regional differences. The total number of thyroidectomies, carried out for multinodular goiter or solitary nodules, was obtained from the Minimal Clinical Summary hospital discharge database. Percentage of people with thyroid diseases going to the general practitioner or the specialist was assessed by means of data about the number of adults using anti-thyroid medications. Food consumption patterns were explored using national food consumption data.

RESULTS

In Flanders, median urinary iodine concentration (UIC) was higher than in Wallonia, 84 μg/L (n = 1,316) and 78 μg/L (n = 1,268), respectively (p < 0.001). There were no differences in goiter prevalence and thyroid volume between the regions among children. Data from the food consumption survey showed a significant higher consumption of seafood in Flanders compared to Wallonia. Further, it was observed that the number of thyroidectomies, carried out for MNG or solitary nodules, and the use of anti-thyroid medication were significantly higher in Wallonia than in Flanders.

CONCLUSION

Iodine status in children was found slightly different in both regions of the country. This finding is in agreement with a higher incidence of thyroidectomies and more extensive use of anti-thyroid medications in the adult population in the region with the lowest iodine excretion.

Value and pitfalls in iodine fortification and supplementation in the 21st century

Although the number of iodine-deficient countries has been reduced by almost 50 % over the last decade, it still remains a frequently misunderstood health problem. The most devastating effects of iodine deficiency occur during fetal development and childhood, periods in which sufficient iodine delivery remains critical. Besides the determination of thyroid size, the concentration of urinary iodine, serum thyroid-stimulating hormone and serum thyroglobulin are useful biomarkers to assess iodine status. Severe iodine deficiency is associated with neurological complications, cretinism, endemic goitre development, hypothyroidism, decreased fertility and increased infant mortality. The recommended iodine supplementation strategies are based on correction of iodine deficiency, close monitoring and evaluation of iodine administration, cooperation of the salt industry, training of local health care professionals and education of the population. Besides the multiple beneficial effects of supplementation, we present in this review a critical look at the possible side effects.

Optimization of iodine intake in Belgium

Mild iodine deficiency (MID) is a long-standing problem in Belgium and was recognized only recently as public health issue by the Ministry of Health (MOH). The main MID-related health problems in Belgium are a high prevalence of thyroid nodules and multinodular goiter. The economic cost of thyroid nodular disease only in Belgium was estimated at about €40 millions per year. The Belgian health authorities adopted a selective strategy to optimize iodine intake through the fortification of bread with iodized salt. A progressive, step-by-step increase of the iodine content of salt was chosen in order to minimize the incidence of hyperthyroidism. MOH monitors this strategy by assessing periodically the urinary iodine concentration in school-aged children and pregnant women, as well as by a yearly follow-up of TSH concentrations in all Belgian newborns. Although the implementation of this strategy was an important step, the main drawback of the current situation is the absence of a legal framework to support the strategy. The utilization of iodized salt in bread on a voluntary basis was endorsed by the bakery industry and MOH. However a legal framework is required to assure the effectiveness and continuity of the program and to avoid a higher than optimal iodine intake in the population.

Iodine intake as a determinant of thyroid disorders in populations

Depending on the availability of iodine, the thyroid gland is able to enhance or limit the use of iodine for thyroid hormone production. When compensation fails, as in severely iodine-deficient populations, hypothyroidism and developmental brain damage will be the dominating disorders. This is, out of all comparison, the most serious association between disease and the level of iodine intake in a population. In less severe iodine deficiency, the normal thyroid gland is able to adapt and keep thyroid hormone production within the normal range. However, the prolonged thyroid hyperactivity associated with such adaptation leads to thyroid growth, and during follicular cell proliferation there is a tendency to mutations leading to multifocal autonomous growth and function. In populations with mild and moderate iodine deficiency, such multifocal autonomous thyroid function is a common cause of hyperthyroidism in elderly people, and the prevalence of thyroid enlargement and nodularity is high. The average serum TSH tends to decrease with age in such populations caused by the high frequency of autonomous thyroid hormone production. On the other hand, epidemiological studies have shown that hypothyroidism is more prevalent in populations with a high iodine intake. Probably, this is also a complication to thyroid adaptation to iodine intake. Many thyroid processes are inhibited when iodine intake becomes high, and the frequency of apoptosis of follicular cells becomes higher. Abnormal inhibition of thyroid function by high levels of iodine is especially common in people affected by thyroid autoimmunity (Hashimoto's thyroiditis). In populations with high iodine intake, the average serum thyroid-stimulating hormone (TSH) tends to increase with age. This phenomenon is especially pronounced in Caucasian populations with a genetically determined high tendency to thyroid autoimmunity. A small tendency to higher serum TSH may be observed already when iodine intake is brought from mildly deficient to adequate, but there is at present no evidence that slightly elevated serum TSH in elderly people leads to an increase in morbidity and mortality.

CONCLUSION

Even minor differences in iodine intake between populations are associated with differences in the occurrence of thyroid disorders. Both iodine intake levels below and above the recommended interval are associated with an increase in the risk of disease in the population. Optimally, iodine intake of a population should be kept within a relatively narrow interval where iodine deficiency disorders are prevented, but not higher. Monitoring and adjusting of iodine intake in a population is an important part of preventive medicine.

Estimation of iodine intake from various urinary iodine measurements in population studies

BACKGROUND

Iodine intake is often measured by a surrogate measure, namely urine iodine excretion as almost all ingested iodine is excreted in the urine. However, the methods for urine collection and the reporting of the results vary. These methods, and their advantages and disadvantages, are considered in this article.

SUMMARY

There are two main ways in which urine can be collected for iodine measurement. The first is the collection of urine over a period, usually 24 hours. The second is the collection of a spot urinary sample. Urinary iodine values can be expressed as the content or concentration and reported without modification or as a function of creatinine in the same sample. The 24-hour urine for iodine measurement is often considered as the "reference standard" for giving a precise estimate of the individual iodine excretion and thereby iodine intake. As 24-hour collections are difficult to perform for large number of persons, single spot urinary samples are preferable to the 24-hour urinary collections in population studies. The iodine concentration in urine depends on the intake of both iodine and fluid. This, and the fact that there is a considerable variability in the daily iodine intake, makes the iodine measurement in spot urine samples unreliable for evaluating individuals for iodine deficiency, though they can be used to screen for exposure to large amounts of iodine from sources such as amiodarone and certain radiographic contrast agents. In populations of at least 500 subjects, the median value of spot urinary iodine concentration is a reliable measure of the iodine intake in the population as there is a leveling out of the day-to-day variation in iodine intake and urinary volume. Expressing the urinary iodide concentration as a function of urinary creatinine is useful in correcting for the influence of fluid intake. When doing so, it is recommended to adjust for the age- and sex-specific creatinine excretion in the given population.

CONCLUSION

In studies of iodine intake, the correct choice of the method for collecting urine and the format for expressing the results of urine iodine measurement is essential to avoid misinterpretation of data on the iodine status of a population or individuals.

Iodine status in pregnancy: role of dietary habits and geographical origin

OBJECTIVES

A study was conducted on iodine status during pregnancy and its dependence on dietary habits, racial and geographical origin, and time since arrival in Italy.

DESIGN AND METHODS

We enrolled 322 consecutive pregnant women: 217 Italians, 62 Eastern Europeans and 43 from Northern and Central Africa. All women completed a food frequency questionnaire on their dietary habits. The urinary iodide concentration (UIC) was determined in spot morning urine samples.

RESULTS

In the group as a whole, the median UIC was 83 microg/l; the UIC was < 50 in 33% and of 150 microg/l or more in 27%; it was significantly lower in Africans and Eastern Europeans than in Italians (medians 45 and 46 vs. 100 microg/l, respectively, P = 0.005). For the foreign women, there was a significant correlation between UIC and time since arrival in Italy (r = 0.22, P = 0.02). A significant link emerged between UIC and cow's milk intake (P = 0.0001). Iodine supplements were used by 40% of the women, and UIC were higher in those who did so than in those who did not (median 103 vs. 75 microg/l, P = 0.03), particularly if the latter did not drink milk (median 98 vs. 42 microg/l, P = 0.01). Multivariate analysis showed that milk was the only variable influencing UIC (OR 1.29, P = 0.0005).

CONCLUSIONS

(i) Iodine levels are too low among pregnant women in our region, and particularly in foreign women. (ii) Cow's milk intake is their main source of iodine. (iii) Iodine supplementation is mandatory during pregnancy, particularly for women do not drink milk.

Assessment of intertrimester and seasonal variations of urinary iodine concentration during pregnancy in an iodine-replete area

OBJECTIVE

To assess intertrimester and seasonal variations in urinary iodine concentration (UIC) among pregnant women.

PATIENTS AND MEASUREMENTS

Pregnant Tehranian women, with no history of thyroid ablation or consumption of thyroid-affecting medication were selected consecutively from November 2004 to November 2006. Morning spot urine samples were collected from each participant during the first, second and third trimesters of pregnancy. Of 466 participants, 298 completed the study in all three trimesters of pregnancy. UIC < 150, 150-250, and > 250 microg/l indicated low, adequate, and high levels, respectively. UIC was measured using a modified Sandell-Kolthoff digestion method.

RESULTS

The pregnant women were aged 25.0 +/- 5.0 (range 16-48) years. Median UIC did not show seasonal fluctuations during pregnancy. However, median (range) UIC was 193 (19-840), 159 (16-640), and 141 (16-400) microg/l in the first, second and third trimesters of pregnancy, respectively (P < 0.0001). Frequency distributions of low, adequate and excessive UIC were 33.2, 31.2 and 35.6% in the first trimester, 46.0, 28.9 and 25.2% in the second trimester, and 53.4, 30.9 and 15.8% in the third trimester of pregnancy, respectively (P < 0.0001). Women with UIC < 150 were more frequently represented in the second vs. the first (P = 0.043; odds ratio 1.49, 95% confidence interval 1.012-2.213) and in the third vs. the first (P = 0.013; odds ratio 1.62, 95% confidence interval 1.108-2.379) trimesters of pregnancy than the 150-250 microg/l group were. UIC decreased throughout pregnancy in all seasons.

CONCLUSIONS

Iranian national salt iodization may prevent seasonal fluctuations of UIC but does not maintain median UIC within adequate and recommended ranges throughout pregnancy. Extra iodine supplementation during pregnancy is recommended.

Longitudinal examination of 24-h urinary iodine excretion in schoolchildren as a sensitive, hydration status-independent research tool for studying iodine status

BACKGROUND

Because worldwide iodine status (IS) depends on continuous fortification, the adequacy of IS needs to be regularly monitored.

OBJECTIVE

Our study aimed to evaluate IS in a longitudinal sample of healthy schoolchildren who regularly used table salt iodized with 20 microg I/g.

DESIGN

Urine osmolality (Uosm) and 24-h urinary excretion rates of iodine (24-h UI), sodium, creatinine, and total urine volume (24-h Uvol) were measured in 1046 specimens that were collected at repeated intervals from 1996 to 2003 in a sample of 358 German children aged 6-12 y. Energy intake and food consumption were calculated from 3-d weighed dietary records that were collected in parallel to the urine samples.

RESULTS

During the 4-y period from 1996 to 1999, the median 24-h UI increased from 87 to 93 microg I/d (P = 0.017), whereas urinary iodine concentration (UIC), Uosm, and 24-h Uvol did not change significantly. Thereafter (from 2000 to 2003), UIC stagnated and Uosm decreased (P = 0.004), whereas 24-h Uvol (P = 0.008) and 24-h UI (P = 0.002) increased. The final median 24-h UI reached 120 microg I/d. Milk, fish, egg, and meat intakes and 24-h sodium excretion were all significant predictors of IS, with an almost doubled contribution from milk intake during the second 4-y period.

CONCLUSIONS

Our study shows a continuous improvement of IS in a longitudinal sample of German schoolchildren. This improvement was masked when UIC was used as an IS index, especially from 2000 to 2003 because of changes in hydration status. Thus, in research-oriented studies that focus on UIC measurements, hydration status can be a relevant confounder. Longitudinal analyses of 24-h UI in cohort studies may represent an alternative hydration status-independent tool to examine trends in IS and the contribution of relevant foods to IS.

Restricted intraindividual urinary iodine concentration variability in nonfasting subjects

OBJECTIVE

Individual urinary iodine concentration (UIC) reflects iodine intake over a short time prior to sampling. Since eating habits are relatively constant in single subjects, UIC should be relatively constant in a given individual. The aim of our study was to verify this hypothesis by assessing UIC in repeated single urine samples from a group of healthy subjects.

DESIGN AND SETTING

A prospective sequential investigation was performed in 131 volunteer health workers or students recruited in our University hospital.

INTERVENTIONS

Single urine samples were taken in a nonfasting state, between 0900 and 1100 hours. Group 1 was composed by 131 subjects who collected one urine sample. Group 2 was composed by 11 subjects of the group 1, who collected multiple repeated urine samples (as a whole 158 urine samples, mean 14 samples each). UIC mean+/-s.d., median and coefficient of variation (CV%) was measured in both groups.

RESULTS

Interindividual UIC variation was wide, UIC ranging from 21 to 382 microg/l, mean 136+/-84 microg/l, median 124 microg/l, CV 62%. Also in the 11 subjects repeatedly sampling there were considerable differences among individual UIC average levels (ranging from 37+/-15 to 221+/-91 microg/l). However, in this second group, the intraindividual variation was considerably restricted (CV% 36).

CONCLUSIONS

The present study shows that in a nonfasting state in mid-morning UIC is more stable from day to day in a single subject, depending on his eating habits, than in various subjects. Thus, a single urine sample even in nonfasting state may give some rough information about the individual's iodine status.

Spectrophotometric determination of urinary iodine by the Sandell-Kolthoff reaction subsequent to dry alkaline ashing. Results from the Czech Republic in the period 1994–2002

The Czech Republic is an iodine-deficient area. Insufficient iodine intake was reduced by enriching cooking salt with iodine in the range 20–34mgI/kg. An important indicator for tracking changes in iodine nutrition over time is accurate information about urinary iodine concentrations in the population. In this paper we describe and characterize our method used for the determination of iodine in biological material, which is based on alkaline ashing of urine specimens preceding Sandell-Kolthoff reaction using brucine as a colorimetric marker. The losses of radioiodine added during sample preparation have not exceeded 0.001%. The detection limit is 2.6μgI/L and the limit of quantification is 11.7μgI/L, with intra-assay precision of 4% and inter-assay precision of 4.9%. During the period 1994–2002, the urinary iodine concentration was determined in 29,612 samples in the Institute of Endocrinology. The mean basal urinary iodine concentrations±SD were 115±69μgI/L. Of the samples, 0.7% were in severe (<20μgI/L), 9.6% in moderate (20–49μgI/L), 40.1% in mild (50–99μgI/L), 35.6% in adequate (100–200μgI/L), and 14.0% in more than adequate (>200μgI/L) subsets of iodine nutrition. A statistically significant (p<0.00001) difference was found between mean male (127μgI/L) and female (112μgI/L) urinary iodine, and an inversely proportional trend also exists in the age-related data.

Milk represents an important source of iodine in schoolchildren of the Veneto region, Italy

The aim of the present study is to evaluate the relationships between urinary iodine concentration (UIC) and the intake of milk and other foods, in a group of school children of the Veneto region, in North East Italy. A questionnaire, concerning the daily intake of milk, yoghurt, cheese and other animal foodstuffs, was distributed to 233 schoolchildren aged between 11 and 15 yr. The use of iodized salt was also investigated. UIC was measured in a casual urine sample of all children investigated. The iodine content of 28 samples of milk and of 13 samples of yoghurt, bought during the summer in shops of the same area, was measured. UIC values ranged between 25 and 436 microg/l, median value was 140 microg/l, mean value 149+/-78 microg/l. The median iodine content of milk and yoghurt were 278 microg/l and 216 microg/l, respectively. With regard to dietary habits, about 70% of the children took 200 ml of milk or more per day, which corresponds to a daily intake of iodine ranging between 50 and 100 microg a day. About 30% of schoolchildren used iodized salt. A highly significant correlation between UIC and milk intake was observed (p=0.0005), while the relationship was poor or absent in the case of both intake of other foodstuffs and use of iodized salt (p=0.38). In conclusion, the results of the study document the very important role of cows' milk as a source of iodine in childhood in the Veneto region, Italy.

Pilot study of urinary iodine concentration and of biochemical thyroid parameters before and after cautious public health intervention on salt iodide content: The Swiss longitudinal 1996–2000 iodine study

OBJECTIVE AND DESIGN

Iodide concentration (IC) in salt was cautiously increased in Switzerland (15 --> 20 ppm iodide). We evaluated the dynamics of the effect of this intervention on urinary iodine concentration (UIC, microg/l) and on thyroid parameters.

SETTING

University Hospital in Bern, Switzerland.

SUBJECTS

A cohort of 36 subjects (12 children, 11 women, 13 men) out of 44 were recruited.

INTERVENTIONS

During the study periods PRE (May 1996-May 1998) and POST (October 1998-December 2000, subdivided into equal subperiods POST1 and POST2), that is, before and after the increase of IC in salt, subjects collected 6248 urine spots for analysis of UIC. Thyroid volumes (n=2/subject) and serum thyroid parameters (n=8/subject) were sequentially evaluated.

METHODS

Average PRE-POST data were compared (multiple regression analysis).

RESULTS

UIC increased overall by 5.1% (P=0.0003). Increase of UIC was highest in children (11.3%, P<0.0001), significant in women (8%, P=0.0016), but not significant in men (P=0.143). Comparison between periods POST1 and POST2 showed that UIC changed more gradually in women than in children. Thyroid volumes were normal, no nonphysiological change occurred. TSH indicated euthyroidism; it decreased in children (1.98 ==> 1.74 mU/l, P=0.04) and increased in men (1.65 ==> 1.91mU/l, P=0.025). FT3 decreased in children (P<0.004) and FT4 decreased in men (P=0.017), both within normal ranges. TSH, FT3 and FT4 were unchanged in women. FT3/FT4 ratios were stable. Anti-TPO-Ab titers were stable (P=0.9). Anti-Tg-Ab titers decreased (P=0.009).

CONCLUSION

The significant UIC effects were of uncertain metabolic relevance. No pathological side effects occurred. Differential delays and penetrances of UIC increase in children and adults were hitherto unknown. The unspectacular stepwise policy seems to be safe. Our pilot results in a population with moderate iodine deficiency in women should be confirmed in population-based cluster studies.

SPONSORSHIP

This work was supported by grants from the University Hospital in Bern, the Swiss Federal Office of Public Health (SFOPH), the 'Swiss National Foundation for Scientific Research' (32-49424.96), the 'Fondation Genevoise de Bienfaisance Valerie Rossi di Montelera', the 'Schweizerische Lebensversicherungs- und Rentenanstalt' and the 'Schüpbach Foundation of the University of Bern'.

Quantification of urinary iodine: a need for revised thresholds

OBJECTIVE

To compare different possibilities of reporting the iodine supply in the same urine samples. Indeed, in field studies, urinary iodine concentration (I/L: micro g I/L, micro mol I/L, I/creatinine: micro g I/g creatanine, micro mol I/mol creatinine) is more readily available than excretion (I/24h micro g I/24 h, micro mol I/24h). However, confusion exists regarding the comparability of iodine supply based upon I/L, I/creatinine and I/24h, which for decades have been regarded as biochemically equivalent.

DESIGN

We compared I/24h, I/L and I/creatinine in accurate 24 h collections of urine and I/L and I/creatinine in 47 spot urine samples.

PATIENTS

A total of 13 subjects (Bern n=7, Brussels n=6) collected a total of 110 precise 24 h urine collections (Bern n=63, Brussels n=47). The subjects from Brussels also took a spot sample at the beginning of each 24 h collection.

RESULTS

Iodine supply in both places was mildly deficient according to the criteria of WHO; all but one collection indicated an intake of >0.39 micro mol I/24h (>50 micro g I/24h). The same data presented as I/creatinine (or I/L) indicated an iodine intake of <0.39 (<50 micro g I/24h) in 5% (24%) of the samples in Bern and 23% (57%) in Brussels. Similar findings were observed for 47 spot samples. Whatever the cut-off selected, I/creatinine and I/L were systematically lower than I/24h (P<0.0002). Creatinine showed smaller CV than volume but did not perform better in defining iodine intake.

CONCLUSION

Considering I/24h as a reference, both I/creatinine and I/L clearly underestimate the iodine intake in subjects with adequate proteoenergetic intake. The significant deviations observed illustrate the urgent need for establishing separate ranges for I/24h, I/creatinine and I/L. In population studies, these deviations might even be larger.

Urinary iodine concentration during pregnancy in an area of unstable dietary iodine intake in Switzerland

We prospectively investigated urinary iodine concentration (UIC) in pregnant women and in female, non-pregnant controls in the canton of Berne, Switzerland, in 1992. Mean UIC of pregnant women [205 +/- 151 microg iodine/g creatinine (microg l/g Cr); no. = 153] steadily decreased from the first (236 +/- 180 microg l/g Cr; no. = 31) to the third trimester (183 +/- 111 microg l/g Cr, p < 0.0001; no. = 66) and differed significantly from that of the control group (91 +/- 37 microg l/g Cr, p < 0.0001; no. = 119). UIC increased 2.6-fold from levels indicating mild iodine deficiency in controls to the first trimester, demonstrating that high UIC during early gestation does not necessarily reflect a sufficient iodine supply to the overall population. Pregnancy is accompanied by important alterations in the regulation of thyroid function and iodine metabolism. Increased renal iodine clearance during pregnancy may explain increased UIC during early gestation, whereas increased thyroidal iodine clearance as well as the iodine shift from the maternal circulation to the growing fetal-placental unit, which both tend to lower the circulating serum levels of inorganic iodide, probably are the causes of the continuous decrease of UIC over the course of pregnancy. Mean UIC in our control group, as well as in one parallel and several consecutive investigations in the same region in the 1990s, was found to be below the actually recommended threshold, indicating a new tendency towards mild to moderate iodine deficiency. As salt is the main source of dietary iodine in Switzerland, its iodine concentration was therefore increased nationwide in 1998 for the fourth time, following increases in 1922, 1965 and 1980.