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

Reference values for plasma and urine trace elements in a Swiss population-based cohort

OBJECTIVES

Trace elements (TEs) are ubiquitous. TE concentrations vary among individuals and countries, depending on factors such as living area, workplaces and diet. Deficit or excessive TEs concentrations have consequences on the proper functioning of human organism so their biomonitoring is important. The aim of this project was to provide reference values for TEs concentrations in the Swiss population.

METHODS

The 1,078 participants to the SKiPOGH cohort included in this study were aged 18-90 years. Their 24-h urine and/or plasma samples were analyzed by inductively coupled plasma mass spectrometry (ICP-MS) to determine 24 TEs concentrations: Ag, Al, As, Be, Bi, Cd, Co, Cr, Cu, Hg, I, Li, Mn, Mo, Ni, Pb, Pd, Pt, Sb, Se, Sn, Tl, V and Zn. Statistical tests were performed to evaluate the influence of covariates (sex, age, BMI, smoking) on these results. Reference intervals for the Swiss adult population were also defined.

RESULTS

TEs concentrations were obtained for respectively 994 and 903 persons in plasma and urine matrices. It was possible to define percentiles of interest (P50 and P95) for almost all the TEs. Differences in TEs distribution between men and women were noticed in both matrices; age was also a cofactor.

CONCLUSIONS

This first Swiss biomonitoring of a large TEs-panel offers reference values in plasma and in urine for the Swiss population. The results obtained in this study were generally in line with clinical recommendations and comparable to levels reported in other population-based surveys.

Iodine intake in the Swiss population 100 years after the introduction of iodised salt: a cross-sectional national study in children and pregnant women

PURPOSE

The Swiss voluntary salt iodisation programme has successfully prevented iodine deficiency for 100 years, but dietary habits are changing and today only one-third of processed foods contain iodised salt. We aimed to monitor the current iodine status in children and pregnant women.

METHODS

We conducted a nationwide cross-sectional study in children (6-12 years) and pregnant women and measured the urinary iodine concentration (UIC) in spot urine samples. We estimated the iodine intake using UIC and urinary creatinine concentration (UCC) and determined the prevalence of intakes below the average requirement (AR) using the SPADE method. We measured dried blood spot (DBS) thyroglobulin (Tg), TSH and total T4 in pregnant women.

RESULTS

The median UIC was 127 μg/L (bootstrapped 95% CI 119, 140, n = 362) in children and 97 μg/L (bootstrapped 95% CI 90, 106, n = 473) in pregnant women. The estimated prevalence of inadequate iodine intake (< 65 μg/day) was 5.4% (bootstrapped 95% CI 0.0, 14.6) in children. Half (47%) of the women consumed iodine-containing multivitamin and mineral supplements (≥ 150 μg/day). Compared to non-users, users had higher median UIC (129 vs. 81 μg/L, P < 0.001), lower prevalence of inadequacy (< 160 μg/day; 0.2 vs. 31%) and lower DBS-Tg (23 vs. 29 μg/L, P < 0.001). All women were euthyroid.

CONCLUSIONS

The Swiss diet and current salt fortification provides adequate iodine intake in children, but not in all pregnant women. Iodine supplements cover the dietary gap in pregnancy but are not universally consumed. Therefore, improved use of iodised salt in processed foods is desired to ensure adequate iodine intake in all population groups. This trial was registered at clinicaltrials.gov as NCT04524013.

National monitoring of iodine, sodium, and vitamin D status in toddlers and women of childbearing age - results and lessons learned from a pilot study in Norway

Background

Norway is lacking a population-based national monitoring program for iodine, sodium, and vitamin D status.

Objective

The aim of this study was to pilot-test a study design for collecting biological samples from a country-representative sample of 2-year-old children and their mothers and to report results for iodine, salt, and vitamin D at baseline, before initiation of salt iodization in Norway.

Design

In a cross-sectional study, we recruited 2-year-old children and their mothers during the routine 2-year check-up through 38 randomly selected health clinics in 2021. Spot urine samples were analyzed for iodine, creatinine, and sodium, and dried blood spots from the mothers were analyzed for thyroglobulin (Tg) and 25-hydroxyvitamin D (25(OH)D).

Results

We aimed at including 400 mother-child pairs but recruited only 55 pairs. Major challenges were closed health clinics due to the COVID-19 pandemic, lack of motivation of the health personnel to prioritize recruiting, missing information about non-participation, and high workload for participants. The median urinary iodine concentration (UIC) was 123 (95% CI: 76, 228) µg/L in the toddlers and 83 (95% CI: 72, 99) µg/L in the mothers. The median urinary sodium concentration (UNaC) was 62 (95% CI: 37, 91) mmol/L in the toddlers and 93 (95% CI: 77, 107) mmol/L in the mothers. Of the mothers, 18% had levels of 25(OH)D <50 nmol/L (suboptimal status).

Discussion and conclusion

Lessons learned from the pilot study will be used to design a national monitoring program for toddlers and women of childbearing age in Norway. The results indicate that 2-year-old children and women of childbearing age in Norway may have inadequate iodine intakes at the group level, while for vitamin D, most of the mothers had adequate status.

Iodine intake assessment in the staff of a Porto region university (Portugal): the iMC Salt trial

PURPOSE

Iodine deficiency disorder (IDD) is an ongoing worldwide recognized problem with over two billion individuals having insufficient iodine intake. School-aged children and pregnant women are often target groups for epidemiological studies, but there is a lack of knowledge on the general adult population. The aim of this study was to assess the iodine status among a Portuguese public university staff as a proxy for the adult working population.

METHODS

The population study covered 103 adults within the iMC Salt randomized clinical trial, aged 24-69 years. Urinary iodine concentration was measured spectrophotometrically using the Sandell-Kolthoff reaction. Iodine food intake was assessed using a 24-h dietary recall. The contribution of discretionary salt to the iodine daily intake was assessed through 24-h urinary sodium excretion (UIE) and potentiometric iodine determination of household salt.

RESULTS

The mean urine volume in 24 h was 1.5 L. The median daily iodine intake estimated from 24-h UIE was 113 µg/day, being lower among women (p < 0.05). Only 22% of participants showed iodine intake above the WHO-recommended cutoff (150 µg/day). The median daily iodine intake estimated from the 24-h dietary recall was 58 µg/day (51 and 68 µg/day in women and men, respectively). Dairy, including yoghurt and milk products, were the primary dietary iodine source (55%). Iodine intake estimated from 24-h UIE and 24-h dietary recall was moderately correlated (Spearman rank correlation coefficient r = 0.34, p < 0.05). The average iodine concentration in household salt was 14 mg I/kg, with 45% of the samples below the minimum threshold preconized by WHO (15 mg I/kg). The contribution of discretionary salt to the daily iodine intake was around 38%.

CONCLUSION

This study contributes new knowledge about iodine status in Portuguese working adults. The results revealed moderate iodine deficiency, particularly in women. Public health strategies and monitoring programs are needed to ensure iodine adequacy in all population groups.

A new innovative breakthrough in the production of salt from bittern using a spray dryer

Spray dryer had long been used to dry liquid materials and produce dry crystalline products. However, the drying of the bittern to produce quality salt crystals has not been widely published. Therefore, the purpose of this study was to examine the effect of drying conditions of the bittern using a spray dryer to produce salt with a high natrium chloride (NaCl) content. Drying was carried out in the hot air temperature (105-125 °C), drying air flow rate (25-45 ml/min), feed flow rate (20-30 ml/min), and concentration of maltodextrin (10-30%). The parameters were observed water content, NaCl content, yield, and mean particle diameter size (MPDS). The results showed that the inlet air temperature of 125 °C can significantly reduce the water content faster and produce higher NaCl levels than the inlet air temperature of 105 °C. The salt crystals produced at higher maltodextrin concentrations have lower water content and high NaCl content. The best-operating conditions are at a hot air temperature of 125 °C, a drying airflow rate of 45 m/s, and a maltodextrin concentration of 25% because it produces salt crystals with high NaCl content. Overall, these results indicate that the bittern can be dried using a spray dryer with potential NaCl content as a raw material for the pharmaceutical industry.

Trends in Iodine Status Among U.S. Children and Adults: A Cross-Sectional Analysis of National Health and Nutrition Examination Survey Data from 2001-2004 to 2017-2020

Background: Iodine nutrition is an important public health issue. Trends in iodine status over time among U.S. schoolchildren and adults and factors mediating changes of iodine status were examined. Methods: In this cross-sectional study of National Health and Nutrition Examination Survey (NHANES) data, we estimated trends in the U.S. population using linear regression analyses. Representative samples of U.S. children and adults were enrolled in NHANES 2001-2020. The NHANES cycles were categorized into 5 four-year periods: 2001-2004, 2005-2008, 2009-2012, 2013-2016, and 2017-2020. The final sample sizes of children and adults for analysis were 4288 and 19,661, respectively. The estimated average requirement (EAR) (based on guidelines from the Institute of Medicine), was used to estimate the prevalence rate of inadequate iodine intake. Binary logistic regression analyses were used to investigate the association between iodine status and contributing factors. Results: From 2001-2004 to 2017-2020, among children, urinary iodine concentration (UIC) decreased from 243 to 166 μg/L (p_trend = 0.0057) and prevalence of iodine intake below the EAR rose from 15.4% to 27.6%. In adults, the UIC decreased from 153 to 116 μg/L (p_trend < 0.001) and prevalence of iodine intake below the EAR rose from 15.0% to 17.9%. A higher prevalence rate of iodine intake below the EAR was observed in females compared with males (children, 24.0% vs. 16.5%, p < 0.001; adults, 20.0% vs. 11.1%, p < 0.001). Inadequate iodine intake was less frequent among non-Hispanic White and Hispanic compared with non-Hispanic Black in children and adults. Adults without thyroid problems had a higher prevalence of inadequate iodine intake than those with thyroid problems (16.0% vs. 13.0%, p = 0.001). Inadequate iodine intake was less likely in the children who "sometimes" and "often" consumed milk products compared with children who "never or rarely" consumed milk products (OR = 0.60 [CI 0.30-1.21] and OR = 0.24 [CI 0.13-0.43], respectively). The prevalence of inadequate iodine intake among adults reporting "sometimes" (OR = 0.70 [CI 0.58-0.83]) and "often" consuming milk products was lower than those who "never or rarely" consumed them (OR = 0.36 [CI 0.30-0.44]). Conclusions: In this weighted survey, the prevalence of inadequate iodine intake increased from 2001-2004 to 2017-2020 among U.S. school-age children and adults. Sex, race, thyroid problems, and a decreased intake of milk products were significantly associated with iodine intake below the EAR.

The DONALD study as a longitudinal sensor of nutritional developments: iodine and salt intake over more than 30 years in German children

Purpose

Mild-to-moderate iodine deficiency was present in large parts of Germany up to the beginning 1990s and improved from then on. Current epidemiological data on spot urine iodine measurements in German children strongly suggest the re-occurrence of an impaired iodine status. We thus examined whether this re-occurrence is identifiable in more detail, through iodine analyses of 24-h urine samples of a well-characterized cohort of German children in whom samples have been systematically collected from 1985 onward. As iodized salt is a major source for iodine supply, urinary sodium excretion was additionally studied.

Methods

Daily iodine and sodium excretions were measured in 2600 24-h urine samples collected between 1985 and 2018 by 677 healthy children aged 6–12 years (participants of the DONALD study). These data were compared with 24-h iodine and sodium excretion estimates obtained from spot urine samples collected in the representative German Health Interview and Examination Surveys for Children and Adolescents KiGGS-baseline (2003–2006) and KiGGS-wave-2 (2014–2017).

Results

Between 1985 and1992, DONALD participants started with a median daily iodine excretion level of 40.1 µg/d. Then, during 1993–2003, iodine excretions mounted up to an approximate plateau (~ 84.8 µg/d). This plateau lasted until 2012. Thereafter, iodine concentrations started to decrease again resulting in a median iodine excretion of only 58.9 µg/d in 2018. Sodium excretion, however, had increased. The marked decrease in iodine status along with an abundant sodium excretion corresponded closely with nationwide KiGGS data.

Conclusions

As exemplified for the clearly worsening iodine status in German children, longitudinal cohort studies collecting detailed biomarker-based prospective data have the potential to reliably capture health-relevant nutritional changes and trends, applicable on a more comprehensive and even representative population level.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00394-022-02801-6.

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.

Iodine Intake from Food and Iodized Salt as Related to Dietary Salt Consumption in the Italian Adult General Population

Since the Italian iodoprophylaxis strategy is based on the use of iodized salt, we assessed the relationship between dietary salt consumption and iodine intake in the Italian adult population. We estimated the relative contribution given by the use of iodized salt and by the iodine introduced by foods to the total iodine intake. The study population included 2219 adults aged 25-79 years (1138 men and 1081 women) from all Italian regions, participating to the Osservatorio Epidemiologico Cardiovascolare/Health Examination Survey 2008-2012 (OEC/HES), and examined for sodium and iodine intake in the framework of the MINISAL-GIRCSI Programme. Dietary sodium and total iodine intake were assessed by the measurement of 24 h urinary excretion, while the EPIC questionnaire was used to evaluate the iodine intake from food. Sodium and iodine intake were significantly and directly associated, upon accounting for age, sex, and BMI (Spearman rho = 0.298; p < 0.001). The iodine intake increased gradually across quintiles of salt consumption in both men and women (p < 0.001). The European Food Safety Authority (EFSA) adequacy level for iodine intake was met by men, but not women, only in the highest quintile of salt consumption. We estimated that approximately 57% of the iodine intake is derived from food and 43% from salt. Iodized salt contributed 24% of the total salt intake, including both discretionary and non-discretionary salt consumption. In conclusion, in this random sample of the Italian general adult population examined in 2008-2012, the total iodine intake secured by iodized salt and the iodine provision by food was insufficient to meet the EFSA adequate iodine intake.

Iodine Intake in Norwegian Women and Men: The Population-Based Tromsø Study 2015-2016

Ensuring sufficient iodine intake is a public health priority, but we lack knowledge about the status of iodine in a nationally representative population in Norway. We aimed to assess the current iodine status and intake in a Norwegian adult population. In the population-based Tromsø Study 2015-2016, 493 women and men aged 40-69 years collected 24-h urine samples and 450 participants also completed a food frequency questionnaire (FFQ). The 24-h urinary iodine concentration (UIC) was analyzed using the Sandell-Kolthoff reaction on microplates followed by colorimetric measurement. Iodine intake was estimated from the FFQ using a food and nutrient calculation system at the University of Oslo. The mean urine volume in 24 h was 1.74 L. The median daily iodine intake estimated (UIE) from 24-h UIC was 159 µg/day (133 and 174 µg/day in women and men). The median daily iodine intake estimated from FFQ was 281 µg/day (263 and 318 µg/day in women and men, respectively). Iodine intake estimated from 24-h UIC and FFQ were moderately correlated (Spearman rank correlation coefficient r = 0.39, p < 0.01). The consumption of milk and milk products, fish and fish products, and eggs were positively associated with estimated iodine intake from FFQ. In conclusion, this shows that iodine intake estimated from 24-h UIC describes a mildly iodine deficient female population, while the male population is iodine sufficient. Concurrent use of an extensive FFQ describes both sexes as iodine sufficient. Further studies, applying a dietary assessment method validated for estimating iodine intake and repeated individual urine collections, are required to determine the habitual iodine intake in this population.

Contribution of iodized salt to total iodine and total salt intake in Germany

BACKGROUND

Salt reduction campaigns without a parallel increase of iodine fortification will lead to a worsened iodine status in countries with a relevant salt iodization. A decline in iodine supply bears the risk of higher prevalences of goiter, thyroid nodules, and cognitive delay in children. Against this background, we analyzed the contribution of iodized salt to total iodine and salt intake in Germany and compared the results with data from Switzerland.

METHODS

Analyses were performed with data of the representative German Health-Interview and Examination-Survey for Adults (DEGS1, 2008-2011) using spot urine measurements of creatinine, iodine, and sodium (n = 6738). Median daily iodine and salt intakes were calculated by estimating 24-h iodine and sodium excretions from urinary analyte/creatinine ratios. Linear regressions were used to deduce iodine intake that originates from iodine containing foods (i.e., salt-independent iodine). From this, ingested iodine originating from salt and the proportion of iodized salt to total salt intake were calculated. Data from Switzerland were obtained from the literature.

RESULTS

In Germany, only 42% (52.2 µg/d) of the predicted median total iodine intake (126.2 µg/d), i.e., 12% less than in Switzerland, were found to originate from salt, whereas 73.7 µg/d came from iodine containing foods. 28% (2.6 g/d) of the median salt intake (9.3 g/d) of the German population was calculated to represent iodized salt against 43% in Switzerland.

CONCLUSIONS

Along with an almost identical inherent iodine intake in Germany and Switzerland, the average total iodine intake, the contribution of iodized salt to total iodine intake, and the proportion of iodized salt to total salt are higher in Switzerland than in Germany. Despite this, iodine fortification of table salt has recently been increased in Switzerland from 20 to 25 mg/kg to ensure iodine sufficiency in the population, whereas in Germany fortification still remains at a mean level of 20 mg/kg implying a growing risk of increasing iodine deficiency rates if general salt intake drops.

Population biomonitoring of micronutrient intakes in children using urinary spot samples

PURPOSE

Urinary spot samples are a promising method for the biomonitoring of micronutrient intake in children. Our aim was to assess whether urinary spot samples could be used to estimate the 24-h urinary excretion of potassium, phosphate, and iodine at the population level.

METHODS

A cross-sectional study of 101 children between 6 and 16 years of age was conducted. Each child collected a 24-h urine collection and three urinary spot samples (evening, overnight, and morning). Several equations were used to estimate 24-h excretion based on the urinary concentrations of each micronutrient in the three spot samples. Various equations and spot combinations were compared using several statistics and plots.

RESULTS

Ninety-four children were included in the analysis (mean age: 10.5 years). The mean measured 24-h urinary excretions of potassium, phosphate, and iodine were 1.76 g, 0.61 g, and 95 µg, respectively. For potassium, the best 24-h estimates were obtained with the Mage equation and morning spot (mean bias: 0.2 g, correlation: 0.27, precision: 56%, and misclassification: 10%). For phosphate, the best 24-h estimates were obtained with the Mage equation and overnight spot (mean bias: - 0.03 g, correlation: 0.54, precision: 72%, and misclassification: 10%). For iodine, the best 24-h estimates were obtained with the Remer equation and overnight spot (mean bias: - 8 µg, correlation: 0.58, precision: 86%, misclassification: 16%).

CONCLUSIONS

Urinary spot samples could be a good alternative to 24-h urine collection for the population biomonitoring of iodine and phosphate intakes in children. For potassium, spot samples were less reliable.

Increase of iodine content in brine-salted soft, semi-hard and hard cheeses by diffusion of iodide

Iodised salt (supplemented with potassium iodide) is the primary source of iodine in Switzerland, but it is rarely used in the manufacture of cheese. In the present study, the diffusion of iodide and chloride in experimentally produced soft, semi-hard and hard cheeses was investigated after brine-salting and subsequent ripening with iodised or non-iodised salt. Diffusion of iodide (I^-) and chloride (Cl^-) into the cheeses was monitored by zonal analyses at different times of ripening. The concurrent diffusion of the two ions in the aqueous phase of cheeses was modelled using Fick's law and the apparent diffusion coefficients (D_app) were determined. The results showed that iodide diffuses more slowly into the interior of the cheeses than chloride. Although the ripened cheeses still showed a concentration gradient between rind and centre, an average increase of 402 ± 30 µg kg^-1 iodine was achieved in the edible part of the cheeses treated with iodised salt. Based on a national food survey, the hypothetical contribution of cheese to the dietary iodine intake was estimated. If cheese was produced with iodised salt, it would cover approximately 10% of the recommended daily iodine intake (150 µg d^-1). Therefore, the use of iodised salt in cheese production would make an important contribution to a iodine supply for population groupswith borderline iodine deficiency.

Effects of feed iodine concentrations and milk processing on iodine concentrations of cows' milk and dairy products, and potential impact on iodine intake in Swiss adults

The contribution of milk and dairy products to daily iodine intake is high but variable in many industrialised countries. Factors that affect iodine concentrations in milk and dairy products are only poorly understood. Our aim was to: (1) assess the effect of feed iodine concentration on milk iodine by supplementing five groups of five cows each with one of five dosages from 0-2 mg iodine/kg DM; (2) quantify iodine losses during manufacturing of cheese and yogurt from milk with varying iodine concentrations and assess the effect of cellar-ripening; and (3) systematically measure iodine partitioning during heat treatment and skimming of milk. Milk iodine reached a near-steady state after 3 weeks of feeding. Median milk iodine (17-302 μg/l for 0-2 mg iodine/kg DM) increased linearly with feed iodine (R2 0·96; P < 0·001). At curd separation, 75-84 % of iodine was lost in whey. Dairy iodine increased linearly with milk iodine (semi-hard cheese: R2 0·95; P < 0·001; fresh cheese and yogurt: R2 1·00; P < 0·001), and cellar-ripening had no effect. Heat treatment had no significant effect, whereas skimming increased (P < 0·001) milk iodine concentration by only 1-2 μg/l. Mean daily intake of dairy products by Swiss adults is estimated at 213 g, which would contribute 13-52 % of the adults' RDA for iodine if cow feed is supplemented with 0·5-2 mg iodine/kg DM. Thus, modulation of feed iodine levels can help achieve desirable iodine concentrations in milk and dairy products, and thereby optimise their contribution to human iodine nutrition to avoid both deficiency and excess.

Iodine bioavailability from cow milk: a randomized, crossover balance study in healthy iodine-replete adults

BACKGROUND

Milk and dairy products are considered important dietary sources of iodine in many countries. However, to our knowledge, iodine bioavailability from milk has not been directly measured in humans.

OBJECTIVE

The aim of this study was to compare iodine bioavailability in iodine-replete adults from: 1) cow milk containing a high concentration of native iodine; 2) milk containing a low concentration of native iodine, with the addition of potassium iodide (KI) to assess a potential matrix effect; and 3) an aqueous solution of KI as a comparator; with all 3 containing equal amounts of total iodine (263 µg/250 mL). We also speciated iodine in milk.

DESIGN

We conducted a 3-wk, randomized, crossover balance study in adults (n = 12) consuming directly analyzed, standardized diets. During the 3 test conditions - high intrinsic iodine milk (IIM), extrinsically added iodine in milk (EIM), and aqueous iodine solution (AIS) - subjects collected 24-h urine over 3 d and consumed the test drink on the second day, with 3- or 4-d wash-out periods prior to each treatment. Iodine absorption was calculated as the ratio of urinary iodine excretion (UIE) to total iodine intake. Milk iodine speciation was performed using ion chromatography-mass spectrometry.

RESULTS

Iodine intake from the standardized diet was 195 ± 6 µg/d for males and 107 ± 6 µg/d for females; the test drinks provided an additional 263 µg. Eleven subjects completed the protocol. There was a linear relation between iodine intake and UIE (β = 0.89, SE = 0.04, P < 0.001). There were no significant differences in UIE among the 3 conditions (P = 0.24). Median (range) fractional iodine absorption across the 3 conditions was 91 (51-145), 72 (48-95), and 98 (51-143)% on days 1, 2, and 3, respectively, with day 2 significantly lower compared with days 1 and 3 (P < 0.001). In milk, 80-93% of the total iodine was inorganic iodide.

CONCLUSION

Nearly all of the iodine in cow milk is iodide and although fractional iodine absorption from milk decreases with increasing dose, its bioavailability is high. The trial was registered at clinicaltrials.gov as NCT03590431.

Iodine status of reproductive age women and their toddlers in northern Ghana improved through household supply of iodized salt and weekly indigenous meal consumption

Iodine deficiency (ID) during pregnancy results in pregnancy losses, intrauterine growth retardation, and lower IQ in the offspring. Even after two decades of universal salt iodization (USI) implementation, the efficacy of USI has not been reported in high risk groups in vulnerable regions in Ghana. We aimed to assess and improve ID status in childbearing age women (all lactating women) and their toddlers in northern Ghana, a geographically and socioeconomically vulnerable region. We provided weekly supply of household iodized salt and community-based feeding of native Hibiscus Sabdariffaa leaves meal (HSM) prepared with iodized salt to women and their toddlers in intervention (n = 60) vs. control group (n = 60). At baseline, ID was prevalent in women (36%) and their toddlers (29%). For women, both median UIC values for intervention (57.4 ug/l) and control group (65.1 ug/l) were below the recommended UIC value of 100 ug/l with no significant differences between the two groups (p = 0.2778). At the endpoint, median UIC for the intervention group (123.6 ug/l) was significantly higher (p = 0.008) than the control group (59.7 ug/l). Our results suggest that weekly supply of iodized salt along with the feeding HSM is an effective channel for improving iodine status of economically disadvantaged groups in communities remote from coastal lands. Furthermore, our results suggest that decreased median UIC among lactating mothers does not necessarily imply lower iodine status for their breastfed toddlers. And finally, the observed median UIC<100 ug/l may point to a non-improvement in iodine status for the past decade for Ghana. There is a need to revisit, assess, and ascertain the challenges in preventing populations from attaining the intended benefits of the USI policy in Ghana.

Effectiveness of increased salt iodine concentration on iodine status: trend analysis of cross-sectional national studies in Switzerland

PURPOSE

Despite longstanding voluntary salt iodisation in Switzerland, data suggest inadequate iodine intake in vulnerable population groups. In response, the salt iodine concentration was increased from 20 to 25 mg/kg and we assessed the impact on iodine status.

METHODS

We conducted a cross-sectional national study in school-age children (n = 731), women of reproductive age (n = 353) and pregnant women (n = 363). We measured urinary iodine concentration (UIC) and urinary sodium concentration (UNaC) in spot urine samples. The current median UIC was compared with national data from 1999, 2004 and 2009. We measured TSH, total T4 and thyroglobulin (Tg) on dried blood spot samples collected in women.

RESULTS

The median UIC (bootstrapped 95% CI) was 137 µg/L (131, 143 µg/L) in school children, 88 µg/L (72, 103 µg/L) in women of reproductive age and 140 µg/L (124, 159 µg/L) in pregnant women. Compared to 2009, the median UIC increased modestly in school children (P < 0.001), but did not significantly change in pregnant women (P = 0.417). Estimated sodium intake exceeded the recommendations in all population groups. The prevalence of thyroid disorders in women was low, but Tg was elevated in 13% of the pregnant women.

CONCLUSION

Iodine intake is overall adequate in Swiss school-age children, but only borderline sufficient in pregnant and non-pregnant women, despite high salt intakes and satisfactory household coverage with iodized salt. Our findings suggest increasing the concentration of iodine in salt may not improve iodine intakes in women if iodised salt is not widely used in processed foods.

REGISTRATION

This trial was registered at clinicaltrials.gov as NCT02312466.

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.

New Statistical Approach to Apportion Dietary Sources of Iodine Intake: Findings from Kenya, Senegal and India

Progress of national Universal Salt Iodization (USI) strategies is typically assessed by household coverage of adequately iodized salt and median urinary iodine concentration (UIC) in spot urine collections. However, household coverage does not inform on the iodized salt used in preparation of processed foods outside homes, nor does the total UIC reflect the portion of population iodine intake attributable to the USI strategy. This study used data from three population-representative surveys of women of reproductive age (WRA) in Kenya, Senegal and India to develop and illustrate a new approach to apportion the population UIC levels by the principal dietary sources of iodine intake, namely native iodine, iodine in processed food salt and iodine in household salt. The technique requires measurement of urinary sodium concentrations (UNaC) in the same spot urine samples collected for iodine status assessment. Taking into account the different complex survey designs of each survey, generalized linear regression (GLR) analyses were performed in which the UIC data of WRA was set as the outcome variable that depends on their UNaC and household salt iodine (SI) data as explanatory variables. Estimates of the UIC portions that correspond to iodine intake sources were calculated with use of the intercept and regression coefficients for the UNaC and SI variables in each country’s regression equation. GLR coefficients for UNaC and SI were significant in all country-specific models. Rural location did not show a significant association in any country when controlled for other explanatory variables. The estimated UIC portion from native dietary iodine intake in each country fell below the minimum threshold for iodine sufficiency. The UIC portion arising from processed food salt in Kenya was substantially higher than in Senegal and India, while the UIC portions from household salt use varied in accordance with the mean level of household SI content in the country surveys. The UIC portions and all-salt-derived iodine intakes found in this study were illustrative of existing differences in national USI legislative frameworks and national salt supply situations between countries. The approach of apportioning the population UIC from spot urine collections may be useful for future monitoring of change in iodine nutrition from reduced salt use in processed foods and in households.

The main determinants of iodine in cows’ milk in Switzerland are farm type, season and teat dipping

Milk and dairy products are important iodine sources and contribute about 30–40 % of total iodine in the Swiss diet. Information about variation in milk iodine concentration (MIC) in Switzerland is limited. We examined MIC and its potential determinants in milk from organic and conventional farms. We collected bulk milk samples at 3-month intervals over 1 year from thirty-two farms throughout Switzerland and Aosta valley, North-West Italy. We sampled all feed components including tap water, collected information on farm characteristics, feeding and teat disinfection practices by questionnaire and estimated the cows’ winter and summer iodine intake. Iodine in milk and feed components was measured using inductively coupled plasma MS. The overall median MIC was 87 (range 5–371) µg/l. In multivariate analysis, predictors of MIC were as follows: (1) farm type: median MIC from organic and conventional farms was 55 and 93 µg/l (P=0·022); (2) season: 53, 97 and 101 µg/l in September, December and March (P<0·002); and (3) teat dipping: 97 µg/l withv. 56 µg/l without (P=0·028). In conclusion, MIC varied widely between farms because of diverse farming practices that result in large differences in dairy cow exposure to iodine via ingestion or skin application. Standardisation of MIC is potentially achievable by controlling these iodine exposures. In order for milk to be a stable iodine source all year round, dietary iodine could be added at a set level to one feed component whose intake is regular and controllable, such as the mineral supplement, and by limiting the use of iodine-containing teat disinfectants.

Iodine in Swiss milk depending on production (conventional versus organic) and on processing (raw versus UHT) and the contribution of milk to the human iodine supply

The iodine content in milk depends on various factors, including the season, production system, and location of milk production. The aim of this study was 1) to obtain data on the iodine concentration of conventional and organically produced milk and according to seasons; 2) to compare these actual data with previous measurement data; 3) to study the influence of UHT treatment on the iodine content and 4) to estimate the contribution of organic and conventional milk to the consumer's iodine intake. A total of 110 samples of conventional and organic ultra-heat treated (UHT) whole milk were collected in the period between 1 May 2013 and 30 April 2014 from two large-scale companies, processing milk from two regions in Switzerland. The iodine concentration in organic milk (average 71 ± 25 μg/l) was significantly lower than in conventional milk (average 111 ± 26 μg/l) and varied between suppliers. Milk iodine concentration varied according to the month of collection in organic and conventionally produced milk, with lowest values between August and October (organic milk 42 μg/l; conventional milk 75 μg/l) and highest values in January (organic milk 99 μg/l; conventional milk 145 μg/l). Heat treatment did not influence iodine concentration. Since milk and dairy products are significant source of food-related iodine intake in Switzerland, consumers who prefer organic milk and dairy products are likely to have an inferior iodine status.

The Use and Interpretation of Sodium Concentrations in Casual (Spot) Urine Collections for Population Surveillance and Partitioning of Dietary Iodine Intake Sources

In 2013, the World Health Organization (WHO) called for joint surveillance of population salt and iodine intakes using urinary analysis. 24-h urine collection is considered the gold standard for salt intake assessment, but there is an emerging consensus that casual urine sampling can provide comparable information for population-level surveillance. Our review covers the use of the urinary sodium concentration (UNaC) and the urinary iodine concentration (UIC) from casual urine samples to estimate salt intakes and to partition the sources of iodine intakes. We reviewed literature on 24-h urinary sodium excretion (UNaE) and UNaC and documented the use of UNaC for national salt intake monitoring. We combined information from our review of urinary sodium with evidence on urinary iodine to assess the appropriateness of partitioning methods currently being adapted for cross-sectional survey analyses. At least nine countries are using casual urine collection for surveillance of population salt intakes; all these countries used single samples. Time trend analyses indicate that single UNaC can be used for monitoring changes in mean salt intakes. However; single UNaC suffers the same limitation as single UNaE; i.e., an estimate of the proportion excess salt intake can be biased due to high individual variability. There is evidence, albeit limited, that repeat UNaC sampling has good agreement at the population level with repeat UNaE collections; thus permitting an unbiased estimate of the proportion of excess salt intake. High variability of UIC and UNaC in single urine samples may also bias the estimates of dietary iodine intake sources. Our review concludes that repeated collection, in a sub-sample of individuals, of casual UNaC data would provide an immediate practical approach for routine monitoring of salt intake, because it overcomes the bias in estimates of excess salt intake. Thus we recommend more survey research to expand the evidence-base on predicted-UNaE from repeat casual UNaC sampling. We also conclude that the methodology for partitioning the sources of iodine intake based on the combination of UIC and UNaC measurements in casual urine samples can be improved by repeat collections of casual data; which helps to reduce regression dilution bias. We recommend more survey research to determine the effect of regression dilution bias and circadian rhythms on the partitioning of dietary iodine intake sources.

Salt, blood pressure and cardiovascular risk: what is the most adequate preventive strategy? A Swiss perspective

Among the various strategies to reduce the incidence of non-communicable diseases reduction of sodium intake in the general population has been recognized as one of the most cost-effective means because of its potential impact on the development of hypertension and cardiovascular diseases. Yet, this strategic health recommendation of the WHO and many other international organizations is far from being universally accepted. Indeed, there are still several unresolved scientific and epidemiological questions that maintain an ongoing debate. Thus what is the adequate low level of sodium intake to recommend to the general population and whether national strategies should be oriented to the overall population or only to higher risk fractions of the population such as salt-sensitive patients are still discussed. In this paper, we shall review the recent results of the literature regarding salt, blood pressure and cardiovascular risk and we present the recommendations recently proposed by a group of experts of Switzerland. The propositions of the participating medical societies are to encourage national health authorities to continue their discussion with the food industry in order to reduce the sodium intake of food products with a target of mean salt intake of 5–6 grams per day in the population. Moreover, all initiatives to increase the information on the effect of salt on health and on the salt content of food are supported.

Urinary 24-h creatinine excretion in adults and its use as a simple tool for the estimation of daily urinary analyte excretion from analyte/creatinine ratios in populations

BACKGROUND/OBJECTIVES

The assessment of urinary excretion of specific nutrients (e.g. iodine, sodium) is frequently used to monitor a population's nutrient status. However, when only spot urines are available, always a risk of hydration-status-dependent dilution effects and related misinterpretations exists. The aim of the present study was to establish mean values of 24-h creatinine excretion widely applicable for an appropriate estimation of 24-h excretion rates of analytes from spot urines in adults.

SUBJECTS/METHODS

Twenty-four-hour creatinine excretion from the formerly representative cross-sectional German VERA Study (n=1463, 20-79 years old) was analysed. Linear regression analysis was performed to identify the most important influencing factors of creatinine excretion. In a subsample of the German DONALD Study (n=176, 20-29 years old), the applicability of the 24-h creatinine excretion values of VERA for the estimation of 24-h sodium and iodine excretion from urinary concentration measurements was tested.

RESULTS

In the VERA Study, mean 24-h creatinine excretion was 15.4 mmol per day in men and 11.1 mmol per day in women, significantly dependent on sex, age, body weight and body mass index. Based on the established 24-h creatinine excretion values, mean 24-h iodine and sodium excretions could be estimated from respective analyte/creatinine concentrations, with average deviations <10% compared with the actual 24-h means.

CONCLUSIONS

The present mean values of 24-h creatinine excretion are suggested as a useful tool to derive realistic hydration-status-independent average 24-h excretion rates from urinary analyte/creatinine ratios. We propose to apply these creatinine reference means routinely in biomarker-based studies aiming at characterizing the nutrient or metabolite status of adult populations by simply measuring metabolite/creatinine ratios in spot urines.

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 status assessment in children: spot urine iodine concentration reasonably reflects true twenty-four-hour iodine excretion only when scaled to creatinine

BACKGROUND

Currently, the measurement of urinary iodine concentration (UIC, μg/L) is the recommended parameter to assess iodine status, however, the dependency of UIC on urine volume may limit its use as an accurate parameter for monitoring iodine status in populations. Therefore, our objective was to compare two approaches for the assessment of urinary iodine excretion in spot urine samples: UIC (μg/L) and a creatinine-scaled estimate of 24-hour iodine excretion (est24h-UIEcrea [μg/d]) against actually measured 24-hour urinary iodine excretion rates (24h-UIE, μg/d).

METHODS

Urinary iodine and creatinine were measured both in 24-hour urine samples and parallel collected spot urine samples from 180 healthy participants of the DONALD Study, aged 6-18 years. 24h-UIE was used as quasi-reference for actual iodine status. Published 24-hour creatinine reference values served to calculate est24h-UIEcrea. Correlation analysis, cross-classifications, and Bland-Altman plots were used to evaluate agreement between the different assessment approaches.

RESULTS

Correlation coefficients of 24h-UIE with UIC (r=0.12, r=0.22; p=n.s.) were substantially weaker than with est24h-UIEcrea (r=0.41, r=0.47; p<0.001) in the 6-12 year old and 13-18 year old groups, respectively. Cross-classification into opposite quartiles by UIC was 7% (6-12 year old group) and 15% (13-18 year old group) versus 5% and 3% by est24h-UIEcrea, respectively. Bland-Altman plots indicated greater deviation from 24h-UIE for the UIC versus the est24h-UIEcrea approach.

CONCLUSION

Our findings in children and adolescents clearly show a better comparability of real 24h-UIE with est24h-UIEcrea than with UIC. Whenever highest possible validity is required for iodine status assessment from spot urine sampling, the determination of est24h-UIEcrea appears to be the more accurate monitoring approach.