Urinary iodine concentration follows a circadian rhythm: a study with 3023 spot urine samples in adults and children

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).

Nutritional Status of Iodine in a Group of Pregnant Women from the State of Minas Gerais Correlated with Neonatal Thyroid Function

OBJECTIVE

 To evaluate the iodine sufficiency of pregnant women assisted in a University Hospital of Minas Gerais, and to correlate the urinary concentrations of maternal iodine with the fetal thyroid hormone levels at birth.

METHODS

 Urinary iodine concentrations from 30 pregnant women with a singleton pregnancy and gestational age lower than 20 weeks were analyzed. Occasional samples of the mothers' urine were collected for the urinary iodine concentration dosage, and these were correlated with the newborns' thyroid-stimulating hormone (TSH) levels.

RESULTS

 The median iodine urinary concentration of this study's pregnant women population was 216.73 mcg/l, which is proper for the group, following the World Health Organization (WHO). No cases of neonatal hypothyroidism were reported in the study, which corroborates the iodine sufficiency in this population sample.

CONCLUSION

 This study shows that despite the increased demand for iodine from pregnant women and the Brazilian Health Regulatory Agency (ANVISA) recommendation of 2013 for reduction of salt iodization levels, the population of pregnant women attended in the prenatal ambulatory of normal risk from the Federal University of Minas Gerais is considered sufficient in iodine. As a higher sample is necessary for the confirmation of these findings, it is too early to recommend the universal supplementation of iodine for Brazilian pregnant women, and more studies must be carried out, considering that iodine supplementation for pregnant women in an area of iodine sufficiency is associated to the risks of the fetus's excessive exposure to iodine.

Variability and Seasonal Change of Urinary Selenium, Molybdenum, and Iodine Excretion in Healthy Young Japanese Adults

Selenium (Se), molybdenum (Mo), and iodine (I) are essential trace elements or nutrients and their adequate intake is essential for human health. These elements in foods are easily absorbed from the digestive tract and excreted predominantly into the urine, and their nutritional status is reflected in urinary excretion; however, information on the variability of urinary excretion is limited. To characterize the urinary Se, Mo, and I concentrations and their intra- and inter-individual coefficients of variation (CV), correlation, and seasonal change, spot urine samples were collected from 24 healthy university students, 10 males and 14 females, with the mean age of 20.6 years, for 10 consecutive days in each of the four seasons according to a defined schedule of an interval of 3 months throughout 1 year. The median Se, Mo, and I concentrations for all urine samples (n = 947) were 52.8, 127.0, and 223 μg/L, respectively. The Se and Mo intakes were highest in summer and lowest in spring, while the I intake was highest in autumn and lowest in summer. In all three elements, the intra-individual CVs were smaller than their inter-individual CVs. The log-transformed intra- and inter-individual CVs were 10.5 and 14.7% for Se, 12.3 and 15.1% for Mo, and 15.5 and 18.1% for I. There was no gender difference in Se and I concentrations, while Mo and Mo/Cr values in males were higher than those in females. Our results suggest adequate nutritional status of Se, Mo, and I with a relatively smaller variability of dietary intake except for I in this population.

Is the urinary iodine/creatinine ratio applicable to assess short term individual iodine status in Chinese adults? Comparison of iodine estimates from 24-h urine and timed-spot urine samples in different periods of the day

Background

Urinary iodine concentration (UIC) is routinely used to evaluate the population iodine status while the uniform method for the individual level assessment is uncertain.

Objectives

To explore the 24-h urinary iodine excretion (UIE) in five different periods of the day and the corresponding prediction equations respect by the use of creatinine-corrected UIC.

Methods

We collected 24-h, spot and fasting urine in five periods of the day to estimate 24-h UIE by the six different prediction equations. We compared the estimated creatinine-corrected UIC to the collected 24-h UIE and identified the most suitable equations in each period of the day.

Results

Among the six different prediction equations, the equation of Kawasaki T was the best to estimate the 24-h UIE by fasting urine among Chinese adults. Among the five periods of time, the equation of Knudsen N was the best to estimate the 24-h UIE in the non-morning period.

Conclusion

Urinary iodine status at the individual level could be estimated by different creatinine-based equations at different periods of the day.

Improving Iodine Status in Lactating Women: What Works?

PURPOSE OF REVIEW

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

RECENT FINDINGS

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

Infant Iodine and Selenium Status in Relation to Maternal Status and Diet During Pregnancy and Lactation

Iodine and selenium are essential trace elements. Recent studies indicate that pregnant and lactating women often have insufficient intake of iodine and selenium, but the impact on fetal and infant status is unclear. Here, we assessed iodine and selenium status of infants in relation to maternal intake and status of these trace elements in the birth cohort NICE, conducted in northern Sweden (n = 604). Iodine was measured in urine (UIC) in gestational week 29, and in breast milk and infant urine 4 months postpartum, while selenium was measured in maternal plasma and erythrocytes in gestational week 29, and in breast milk and infant erythrocytes 4 months postpartum, in both cases using ICP-MS. Maternal intake was assessed with semi-quantitative food frequency questionnaires in gestational week 34 and at 4 months postpartum. The median intake of iodine and selenium during pregnancy (98 and 40 μg/d, respectively) and lactation (108 and 39 μg/d, respectively) was below recommended intakes, reflected in insufficient status (median UIC of 113 μg/L, median plasma selenium of 65 μg/L). Also, breast milk concentrations (median iodine 77 μg/L, median selenium 9 μg/L) were unlikely to meet infant requirements. Median UIC of the infants was 114 μg/L and median erythrocyte selenium 96 μg/kg, both similar to the maternal concentrations. Infant UIC correlated strongly with breast milk levels (rho = 0.64, p < 0.001). Their erythrocyte selenium correlated with maternal erythrocyte selenium in pregnancy (rho = 0.38, p < 0.001), but not with breast milk selenium, suggesting formation of prenatal reserves. Our results indicate that the transport of iodine and selenium to the fetus and infant is prioritized. Still, it is uncertain whether most infants had sufficient intakes. Further, the results might indicate an involvement of iodine in asthma development during the first year of life, which is essential to follow up. The low maternal and infant dietary intake of both iodine and selenium, especially when the mothers did not use supplements or iodized table salt, suggest a need for a general screening of women and young children.

Reflection of Dietary Iodine in the 24 h Urinary Iodine Concentration, Serum Iodine and Thyroglobulin as Biomarkers of Iodine Status: A Pilot Study

BACKGROUND

The iodine status of the US population is considered adequate, but subpopulations remain at risk for iodine deficiency and a biomarker of individual iodine status has yet to be determined. The purpose of this study was to determine whether a 3 day titration diet, providing known quantities of iodized salt, is reflected in 24 h urinary iodine concentration (UIC), serum iodine, and thyroglobulin (Tg).

METHODS

A total of 10 participants (31.3 ± 4.0 years, 76.1 ± 6.3 kg) completed three, 3 day iodine titration diets (minimal iodine, US RDA, (United States Recommended Daily Allowance), and 3× RDA). The 24 h UIC, serum iodine, and Tg were measured following each diet. The 24 h UIC and an iodine-specific food frequency questionnaire (FFQ) were completed at baseline.

RESULTS

UIC increased an average of 19.3 μg/L for every gram of iodized salt consumed and was different from minimal to RDA (p = 0.001) and RDA to 3× RDA diets (p = 0.04). Serum iodine was different from RDA to 3× RDA (p = 0.006) whereas Tg was not responsive to diet. Baseline UIC was associated with iodine intake from milk (r = 0.688, p = 0.028) and fish/seafood (r = 0.646, p = 0.043).

CONCLUSION

These results suggest that 24 h UIC and serum iodine may be reflective of individual iodine status and may serve as biomarkers of iodine status.

Iodine Excretion and Intake in Women of Reproductive Age in South Australia Eating Plant-Based and Omnivore Diets: A Pilot Study

Women consuming a strictly vegan/plant-based diet may be at increased risk of low iodine intake due to avoidance of animal products containing iodine. The aim of this pilot study was to determine the iodine excretion and intake in women consuming vegan/plant based diets compared with women consuming omnivore diets. Fifty-seven women (n = 31 plant-based, n = 26 omnivores), provided two spot urine samples to assess urinary iodine concentration (UIC). Two days of dietary intake were also recorded by participants. As the data were not normally distributed results are reported as median (IQR). UIC was significantly different between groups, 44 (26-66) µg/L in the vegan/plant-based group versus 64 (40-88) µg/L in omnivores (p < 0.05). UIC did not meet the >100 µg/L level recommended by the World Health Organization. Iodine intake was also significantly different, 78 (62-91) µg/day in the vegan/plant-based group and 125 (86-175) µg/day in the omnivores (p = 0.000). Iodine intake and bread intake were correlated with iodine excretion (CC 0.410-4.11, p = 0.003). These data indicate iodine insufficiency in both groups of women as the median values were below the minimum WHO recommendation. A larger study assessing iodine excretion in the Australian women of reproductive age who are not pregnant or breastfeeding is needed to confirm these findings.

Mild-to-moderate iodine deficiency in a sample of pregnant women and salt iodine concentration from Zhejiang province, China

Since 2011, Zhejiang province has eliminated iodine deficiency disorders (IDD) in its populations. Following this achievement, a new revised iodine concentration in iodised salt was implemented in Zhejiang in 2012. However, the re-emergence of iodine deficiency has been reported in pregnant women. Therefore, the aim of this study was to assess household salt iodine concentration and iodine status of pregnant women in Zhejiang province, China. We conducted a cross-sectional study between April 2018 and August 2018 in Quzhou, Zhejiang province. Pregnant women aged ≥ 18 years who did not have a history of thyroid disease were recruited into the study. They were asked to complete socio-demographic questionnaires including a food frequency questionnaire (FFQ). In addition, a spot urine sample and a household table salt sample were also provided by each participant. A total of 625 pregnant women agreed to participate. The overall median urinary iodine concentration (UIC) was 130 µg/L, indicating mild-to-moderate iodine deficiency in pregnant women. The coverage of iodised salt was 85.2%, and of these, the rate of adequately iodised salt was 98.1%. In conclusion, our results confirmed the re-emergence of iodine deficiency in pregnant women as reported by other studies conducted in Zhejiang province. Therefore, urgent public health actions are needed to improve iodine status of pregnant women in order to prevent the adverse consequences of IDD on the neurodevelopment of foetus.

A systematic review and meta-analysis of 24-h urinary output of children and adolescents: impact on the assessment of iodine status using urinary biomarkers

PURPOSE

Urinary iodine concentration (UIC (μg/ml) from spot urine samples collected from school-aged children is used to determine the iodine status of populations. Some studies further extrapolate UIC to represent daily iodine intake, based on the assumption that children pass approximately 1 L urine over 24-h, but this has never been assessed in population studies. Therefore, the present review aimed to collate and produce an estimate of the average 24-h urine volume of children and adolescents (> 1 year and < 19 years) from published studies.

METHODS

EBSCOHOST and EMBASE databases were searched to identify studies which reported the mean 24-h urinary volume of healthy children (> 1 year and < 19 years). The overall mean (95% CI) estimate of 24-h urine volume was determined using a random effects model, broken down by age group.

RESULTS

Of the 44 studies identified, a meta-analysis of 27 studies, with at least one criterion for assessing the completeness of urine collections, indicated that the mean urine volume of 2-19 year olds was 773 (654, 893) (95% CI) mL/24-h. When broken down by age group, mean (95% CI) 24-h urine volume was 531 mL/day (454, 607) for 2-5 year olds, 771 mL/day (734, 808) for 6-12 year olds, and 1067 mL/day (855, 1279) for 13-19 year olds.

CONCLUSIONS

These results demonstrate that the average urine volume of children aged 2-12 years is less than 1 L, therefore, misclassification of iodine intakes may occur when urine volumes fall below or above 1 L. Future studies utilizing spot urine samples to assess iodine status should consider this when extrapolating UIC to represent iodine intakes of a population.

Intake of seaweed as part of a single sushi meal, iodine excretion and thyroid function in euthyroid subjects: a randomized dinner study

OBJECTIVE

Globalisation has extended to the kitchen and the Asian cuisine has gained international popularity with sushi and seaweed now being widespread. We explored the possible acute adverse effects of an iodine load from a single sushi-and-seaweed meal as seaweed iodine may induce thyroid dysfunction.

METHODS

Nine euthyroid participants were randomized into three groups: Halibut maki roll with either (A) newly harvested Greenlandic seaweed salad, (B) no seaweed salad on the side, or (C) Japanese seaweed salad purchased at a local store. We collected spot urine and blood samples daily for a week for measurement of iodine and creatinine in urine, thyroid stimulating hormone (TSH), and estimated-free T4 (fT4) in serum.

RESULTS

All participants ingested the full meal and the drop-out was nil. No adverse effects were reported. Pre-meal urinary iodine excretion (UIE) was 75 µg/g. UIE rose (p < 0.001) by 385%, 59% and 43% for groups A, B, and C, peaked in the 6-h spot urine sample at 393, 120, and 109 µg/g, and was down to pre-meal values by day 2. Serum TSH rose (p = 0.012) 150% on day 2 and was down to pre-meal values by day 3. Serum fT4 remained at the same level. No adverse reactions were reported.

CONCLUSION

A sushi meal increased urinary iodine excretion by 40 µg/g, or 400 µg/g if a newly harvested seaweed salad was added. An ensuing rise in serum TSH was brief, and a single sushi meal with seaweed salad did not cause any adverse events.

The Reliability of Iodine Concentration in Diaper-Retrieved Infant Urine Using Urine Collection Pads, and in Their Mothers' Breastmilk

Mild to moderate iodine deficiency is common among women of childbearing age. Data on iodine status in infants are sparse, partly due to the challenges in collecting urine. Urinary iodine concentration (UIC) is considered a good marker for recent dietary iodine intake and status in populations. The aim of this study was to investigate the reliability of iodine concentration measured in two spot-samples from the same day of diaper-retrieved infant urine and in their mothers' breastmilk. We collected urine and breastmilk from a sample of 27 infants and 25 mothers participating in a cross-sectional study at two public healthcare clinics in Norway. The reliability of iodine concentration was assessed by calculating the intraclass correlation coefficients (ICC) and the coefficient of variation (CV). The ICC for infants' urine was 0.64 (95% confidence interval (CI) 0.36-0.82), while the ICC for breastmilk was 0.83 (95% CI 0.65-0.92) Similarly, the intraindividual CV for UIC was 0.25 and 0.14 for breastmilk iodine concentration (BIC). Compared to standard methods of collecting urine for measuring iodine concentration, the diaper-pad collection method does not substantially affect the reliability of the measurements.

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.

The Joint Role of Thyroid Function and Iodine Status on Risk of Preterm Birth and Small for Gestational Age: A Population-Based Nested Case-Control Study of Finnish Women

Normal maternal thyroid function during pregnancy is essential for fetal development and depends upon an adequate supply of iodine. Little is known about how iodine status is associated with preterm birth and small for gestational age (SGA) in mildly iodine insufficient populations. Our objective was to evaluate associations of early pregnancy serum iodine, thyroglobulin (Tg), and thyroid-stimulating hormone (TSH) with odds of preterm birth and SGA in a prospective, population-based, nested case-control study from all births in Finland (2012–2013). Cases of preterm birth (n = 208) and SGA (n = 209) were randomly chosen from among all singleton births. Controls were randomly chosen from among singleton births that were not preterm (n = 242) or SGA (n = 241) infants during the same time period. Women provided blood samples at 10–14 weeks’ gestation for serum iodide, Tg and TSH measurement. We used logistic regression to estimate odds ratios (ORs) and 95% confidence intervals (CIs) for preterm birth and SGA. Each log-unit increase in serum iodide was associated with higher odds of preterm birth (adjusted OR = 1.19, 95% CI = 1.02–1.40), but was not associated with SGA (adjusted OR = 1.01, 95% CI = 0.86–1.18). Tg was not associated with preterm birth (OR per 1 log-unit increase = 0.87, 95% CI = 0.73–1.05), but was inversely associated with SGA (OR per log-unit increase = 0.78, 95% CI = 0.65–0.94). Neither high nor low TSH (versus normal) were associated with either outcome. These findings suggest that among Finnish women, iodine status is not related to SGA, but higher serum iodide may be positively associated with preterm birth.

Consistent Iodine Status Assessment in Chinese Adults by Different Spot Urinary Iodine Concentrations in a Day Together With Corresponding Correction Coefficients

Objective: The aim of this research was to determine the correction coefficients of different spot urinary iodine concentrations (UICs) in a day to predict the early morning UIC, to make the different spot UICs of a day comparable in assessing iodine status in the same population. Methods: In total, 424 participants aged 18 to 28 years were recruited from Tianjin, China. Three spot urine samples were collected from each participant during three periods of the day (6:30-7:00, 10:00-10:30, and 16:00-16:30). A total of 1272 urine samples were collected. A 24-hour dietary record was reported by each participant for 3 consecutive days. Results: Both the UICs at 10:00-10:30 and 16:00-16:30 were higher than that at 6:30-7:00 (181.75 or 198.15μg/L vs 157.69 μg/L; all p < 0.05). Bland-Altman plot showed no good agreements between the other two spot UICs and that at 6:30-7:00 with both Bland-Altman indexes of 7.1%. Correction coefficients used to predict UIC at 6:30-7:00 from the UIC at 10:00-10:30 and 16:00-16:30 were 0.9231 and 0.8592, respectively. The predicted UICs at 6:30-7:00 by using the UIC at 10:00-10:30 and 16:00-16:30 both had no statistically significant difference with the actual UIC at 6:30-7:00 (all p > 0.05). Bland-Altman plot showed good agreements between the predicted UICs and actual UICs at 6:30-7:00 with both Bland-Altman indexes of 4.5%. Conclusions: It was reliable to predict the early morning UIC using correction coefficients of other spot UIC of the day, which gave a new idea for standardizing the methodology of surveys assessing iodine status of a population.

Women Remain at Risk of Iodine Deficiency during Pregnancy: The Importance of Iodine Supplementation before Conception and Throughout Gestation

In Australia, pregnant women are advised to take an iodine supplement (I-supp) (150 µg/day) to reduce risks to the foetus associated with iodine deficiency (ID). To examine the impact of this recommendation on iodine status, and to identify factors that contribute to adequacy during gestation, supplement use and Urinary Iodine Concentration (UIC) was measured in 255 pregnant women (gestation range 6 to 41 weeks) in Tasmania. The median UIC (MUIC) of 133 µg/L (Inter-quartile range 82–233) was indicative of ID, being below the 150–249 µg/L range for adequacy during pregnancy. Women taking an iodine-containing-supplement (I-supp) had a significantly higher MUIC (155 µg/L) (n = 171) compared to the combined MUIC (112.5 µg/L) (n = 84) of those who had never (120 µg/L) (n = 61) or were no longer taking an I-supp (90 µg/L) (n = 23) (p = 0.017). Among women reporting I-supp use, the MUIC of those commencing the recommended 150 µg/day prior to conception was significantly higher than those starting supplementation following pregnancy confirmation: 196 (98–315) µg/L (n = 45) versus 137.5 (82.5–233.5) µg/L (n = 124), p = 0.032. Despite recommendations for iodine supplementation pregnant Tasmanian women remain at risk of ID. Commencing an I-supp of 150 µg/day prior to conception and continuing throughout pregnancy is required to ensure adequacy. Timely advice regarding the importance of adequate iodine nutrition, including supplementation is needed to reduce the risk of irreversible in utero neurocognitive damage to the foetus.

Pre-analytical Factors Influence Accuracy of Urine Spot Iodine Assessment in Epidemiological Surveys

Urinary iodine concentration (UIC) is commonly used to assess iodine status of subjects in epidemiological surveys. As pre-analytical factors are an important source of measurement error and studies about this phase are scarce, our objective was to assess the influence of urine sampling conditions on UIC, i.e., whether the child ate breakfast or not, urine void rank of the day, and time span between last meal and urine collection. A nationwide, two-stage, stratified, cross-sectional study including 1560 children (6-12 years) was performed in 2012. UIC was determined by the Sandell-Kolthoff method. Pre-analytical factors were assessed from children's mothers by using a questionnaire. Association between iodine status and pre-analytical factors were adjusted for one another and socio-economic characteristics by multivariate linear and multinomial regression models (RPR: relative prevalence ratios). Skipping breakfast prior to morning urine sampling decreased UIC by 40 to 50 μg/L and the proportion of UIC < 100 μg/L was higher among children having those skipped breakfast (RPR = 3.2[1.0-10.4]). In unadjusted analyses, UIC was less among children sampled more than 5 h from their last meal. UIC decreased with rank of urine void (e.g., first vs. second, P < 0.001); also, the proportion of UIC < 100 μg/L was greater among 4th rank samples (vs. second RPR = 2.1[1.1-4.0]). Subjects' breakfast status and urine void rank should be accounted for when assessing iodine status. Providing recommendations to standardize pre-analytical factors is a key step toward improving accuracy and comparability of survey results for assessing iodine status from spot urine samples. These recommendations have to be evaluated by future research.

Iodine Status Assessment in South African Adults According to Spot Urinary Iodine Concentrations, Prediction Equations, and Measured 24-h Iodine Excretion

The iodine status of populations is conventionally assessed using spot urinary samples to obtain a median urinary iodine concentration (UIC) value, which is assessed against standard reference cut-offs. The assumption that spot UIC reflects daily iodine intake may be flawed because of high day-to-day variability and variable urinary volume outputs. This study aimed to compare iodine status in a sample of South African adults when determined by different approaches using a spot urine sample (median UIC (MUIC), predicted 24 h urinary iodine excretion (PrUIE) using different prediction equations) against measured 24 h urinary iodine excretion (mUIE). Both 24 h and spot urine samples were collected in a subsample of participants (n = 457; median age 55 year; range 18⁻90 year) in the World Health Organization Study on global AGEing and adult health (SAGE) Wave 2 in South Africa, in 2015. Kawasaki, Tanaka, and Mage equations were applied to assess PrUIE from predicted urinary creatinine (PrCr) and spot UIC values. Adequacy of iodine intake was assessed by comparing PrUIE and mUIE to the Estimated Average Requirement of 95 µg/day, while the MUIC cut-off was.

Inadequate Iodine Intake in Population Groups Defined by Age, Life Stage and Vegetarian Dietary Practice in a Norwegian Convenience Sample

Inadequate iodine intake has been identified in populations considered iodine replete for decades. The objective of the current study is to evaluate urinary iodine concentration (UIC) and the probability of adequate iodine intake in subgroups of the Norwegian population defined by age, life stage and vegetarian dietary practice. In a cross-sectional survey, we assessed the probability of adequate iodine intake by two 24-h food diaries and UIC from two fasting morning spot urine samples in 276 participants. The participants included children (n = 47), adolescents (n = 46), adults (n = 71), the elderly (n = 23), pregnant women (n = 45), ovo-lacto vegetarians (n = 25), and vegans (n = 19). In all participants combined, the median (95% CI) UIC was 101 (90, 110) µg/L, median (25th, 75th percentile) calculated iodine intake was 112 (77, 175) µg/day and median (25th, 75th percentile) estimated usual iodine intake was 101 (75, 150) µg/day. According to WHOs criteria for evaluation of median UIC, iodine intake was inadequate in the elderly, pregnant women, vegans and non-pregnant women of childbearing age. Children had the highest (82%) and vegans the lowest (14%) probability of adequate iodine intake according to reported food and supplement intakes. This study confirms the need for monitoring iodine intake and status in nationally representative study samples in Norway.

Iodine Intakes of Victorian Schoolchildren Measured Using 24-h Urinary Iodine Excretion

Mandatory fortification of bread with iodized salt was introduced in Australia in 2009, and studies using spot urine collections conducted post fortification indicate that Australian schoolchildren are now replete. However an accurate estimate of daily iodine intake utilizing 24-h urinary iodine excretion (UIE μg/day) has not been reported and compared to the estimated average requirement (EAR). This study aimed to assess daily total iodine intake and status of a sample of primary schoolchildren using 24-h urine samples. Victorian primary school children provided 24-h urine samples between 2011 and 2013, from which urinary iodine concentration (UIC, μg/L) and total iodine excretion (UIE, μg/day) as an estimate of intake was determined. Valid 24-h urine samples were provided by 650 children, mean (SD) age 9.3 (1.8) years (n = 359 boys). The mean UIE of 4–8 and 9–13 year olds was 94 (48) and 111 (57) μg/24-h, respectively, with 29% and 26% having a UIE below the age-specific EAR. The median (IQR) UIC was 124 (83,172) μg/L, with 36% of participants having a UIC < 100 μg/L. This convenience sample of Victorian schoolchildren were found to be iodine replete, based on UIC and estimated iodine intakes derived from 24-h urine collections, confirming the findings of the Australian Health Survey.

Urinary iodine: comparison of a simple method for its determination in microplates with measurement by inductively-coupled plasma mass spectrometry

The aim of our study was to develop and validate an inexpensive, rapid, easy to use quantitative method to determine urinary iodine without major procurement costs for equipment. The rationale behind introducing this method is the increasing demand for urinary iodine assessments. Our study included 103 patients (76 female, 27 male), age (arithmetic mean) 52 ± 17.3 years. Urinary iodine was determined in microplates by a modification of the Sandell-Kolthoff reaction. The results were compared with inductively-coupled plasma mass spectrometry (ICP-MS) for iodine, considered as reference method. Geometric mean of urinary iodine determined by the Sandell-Kolthoff reaction method was 62.69 μg/l (95% confidence interval 53.16-73.92) whereas by the ICP-MS method it was 65.53 μg/l (95% confidence interval 54.77-78.41). Passing-Bablok regression equations for both methods gave y = 3.374 + 0.873x (y: Sandell-Kolthoff method, x: ICP-MS). Spearman´s correlation coefficient was 0.981, indicating a very high degree of agreement between the two methods. Bland-Altman plots showed no significant systematic difference between the two methods. The modified Sandell-Kolthoff method using microtiter plate technique presented here is a simple, inexpensive semi-automated method to determine urinary iodine with very little toxic waste. Comparison with the ICP-MS-technique yielded a good agreement between the two methods.

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.

Assessment of the Effect of Two Distinct Restricted Iodine Diet Durations on Urinary Iodine Levels (Collected over 24 h or as a Single-Spot Urinary Sample) and Na(+)/I(-) Symporter Expression

INTRODUCTION

A restricted iodine diet (RID) may be recommended for depletion of the whole-body iodine pool in patients with differentiated thyroid cancer referred for radioiodine treatment or a whole-body scan. Evaluation of the iodine pool is possible through urinary iodide (UI) measurements, which can be collected in 24-hour (24U) or spot urinary (sU) samples. However, the minimum period required for an RID to lower the iodine pool, the measurement of iodine in sU samples as a iodine pool marker, and the influence of the iodine pool on Na(+)/I(-) symporter (NIS) expression are debatable in the literature.

OBJECTIVES

To compare the effects of 15- and 30-day RID on UI measurements in 24U and sU samples and the impact of RID on NIS expression.

METHODS

Thyroidectomized patients went on a 15- or 30-day RID and collected 24U and sU samples before and after the RID. Twenty healthy individuals were evaluated for mRNA NIS expression before and after the RID.

RESULTS

Of 306 patients, only 125 properly complied with both the RID and 24U collection. We observed a correlation between sU and 24U UI before the RID (n = 306, ρ = 0.47, p < 0.001), after a 15-day RID (n = 79, ρ = 0.49, p < 0.001), and after a 30-day RID (n = 46, ρ = 0.73, p < 0.001). There was a significant decrease in UI after the RID. The median UI measurement was 275 μg/l at baseline and 99 and 80 μg/l after a 15- and 30-day RID, respectively. There was a significant increase in NIS expression after a 15-day RID.

CONCLUSIONS

A 15-day RID is sufficient to deplete the iodine pool. sU can replace 24U UI as a marker for assessing the iodine pool. NIS expression was increased after a 15-day RID.

The relationship of central foveal thickness to urinary iodine concentration in retinitis pigmentosa with or without cystoid macular edema

IMPORTANCE

Current treatments for cystoid macular edema (CME) in retinitis pigmentosa (RP) are not always effective, may lead to adverse effects, and may not restore visual acuity. The present research lays the rationale for evaluating whether an iodine supplement could reduce CME in RP.

OBJECTIVE

To determine whether central foveal thickness (CFT) in the presence of CME is related to dietary iodine intake inferred from urinary iodine concentration (UIC) in nonsmoking adults with RP.

DESIGN, SETTING, AND PARTICIPANTS

We performed a cross-sectional observational study of 212 nonsmoking patients aged 18 to 69 years referred to our institution for RP with visual acuity of no worse than 20/200 in at least 1 eye.

EXPOSURE

Retinitis pigmentosa with or without CME.

MAIN OUTCOMES AND MEASURES

With the eye as the unit of analysis, the relationship of log CFT measured by optical coherence tomography to UIC measured from multiple spot samples and represented as a 3-level classification variable (<100, 100-199, and ≥200 µg/L), assigning greater weight to patients with more reliable UIC estimates.

RESULTS

Analyses were limited to 199 patients after excluding 11 who failed to return urine samples for measuring UIC and 2 outliers for UIC. Of the 199 patients, 36.2% had CME in 1 or both eyes. Although log CFT was inversely related to UIC based on findings from all eyes (P = .02), regression of log CFT on UIC separately for eyes with and without CME showed a strong inverse significant relationship for the former group (P < .001) and no significant relationship for the latter group (P = .66) as tested. For the eyes with CME, CFT ranged from a geometric mean of 267 µm for a median UIC of less than 100 µg/L to a geometric mean of 172 µm for a median UIC of 200 µg/L or greater. In contrast, we found no significant association between CME prevalence and UIC based on the entire sample as tested (odds ratio, 1.01 [95% CI, 0.38-2.67]; P = .99).

CONCLUSIONS AND RELEVANCE

A higher UIC in nonsmoking adults with RP was significantly associated with less central foveal swelling in eyes with CME. Additional study is required to determine whether an iodine supplement can limit or reduce the extent of CME in patients with RP.

Challenges in the evaluation of urinary iodine status in pregnancy: the importance of iodine supplement intake and time of sampling

OBJECTIVES

Median urinary iodine concentration (UIC) is the recommended method to evaluate iodine status in pregnancy, but several factors may challenge the interpretation of the results. We evaluated UIC in pregnant women according to (1) sampling in the hospital versus at home, (2) time of the most recent iodine supplement intake prior to sampling, and (3) members of their household.

STUDY DESIGN

Danish cross-sectional study in the year 2012. Pregnant women (n = 158), their male partners (n = 157) and children (n = 51) provided a questionnaire with detailed information on iodine supplement intake and a spot urine sample obtained in the hospital and/or at home for measurement of UIC and urinary creatinine concentration.

RESULTS

In the pregnant women providing a urine sample both in the hospital and at home (n = 66), individual UIC (p = 0.002) and urinary creatinine concentration (p = 0.042), but not estimated 24-hour urinary iodine excretion (p = 0.79), were higher when sampling was at home. Median UIC was dependent on the time of the most recent iodine supplement intake prior to sampling [same day (n = 79): 150 µg/l (95% CI 131-181 µg/l), the day before (n = 51): 105 µg/l (78-131 µg/l), several days ago/non-user (n = 28): 70 µg/l (56-94 µg/l), p < 0.001]. The pattern was similar in the male partners. Apart from a more frequent iodine supplement intake in pregnancy (87.3% vs. partners 15.9%), no systematic differences were observed in urinary measurements between the pregnant women and their partners.

CONCLUSIONS

Time of spot urine sampling and time span from iodine supplement intake to spot urine sampling should be considered when evaluating urinary iodine status in pregnancy.

Comparison of population iodine estimates from 24-hour urine and timed-spot urine samples

BACKGROUND

Median urine iodine concentration (UIC; μg/L) in spot urine samples is recommended for monitoring population iodine status. Other common measures are iodine:creatinine ratio (I/Cr; μg/g) and estimated 24-hour urine iodine excretion (UIE; I/Cr × predicted 24-hour Cr; μg/day). Despite different units, these measures are often used interchangeably, and it is unclear how they compare with the reference standard 24-hour UIE.

METHODS

Volunteers aged 18-39 years collected all their urine samples for 24 hours (n=400). Voids from morning, afternoon, evening, overnight, and a composite 24-hour sample were analyzed for iodine. We calculated median observed 24-hour UIE and 24-hour UIC, and spot UIC, I/Cr, and two measures of estimated UIE calculated using predicted 24-hour Cr from published estimates by Kesteloot and Joosens (varies by age and sex) and published equations by Mage et al. (varies by age, sex, race, and anthropometric measures). We examined mean differences and relative difference across iodine excretion levels using Bland-Altman plots.

RESULTS

Median 24-hour UIE was 173.6 μg/day and 24-hour UIC was 144.8 μg/L. From timed-spot urine samples, estimates were: UIC 147.3-156.2 μg/L; I/Cr 103.6-114.3 μg/g, estimated 24-hour UIE (Kesteloot and Joosens) 145.7-163.3 μg/day; and estimated 24-hour UIE (Mage) 176.5-187.7 μg/day. Iodine measures did not vary consistently by timing of spot urine collection. Compared with observed 24-hour UIE, on average, estimated (Mage) 24-hour UIE was not significantly different, while estimated 24-hour UIE (Kesteloot and Joosens) was significantly different for some ethnicity/sex groups. Compared with 24-hour UIC, on average, spot UIC did not differ.

CONCLUSIONS

Estimates of UIC, I/Cr, and estimated 24-hour UIE (I/Cr × predicted 24-hour Cr) from spot urine samples should not be used interchangeably. Estimated 24-hour UIE, where predicted 24-hour Cr varies by age, sex, ethnicity, and anthropometric measures and was calculated with prediction equations using data from the sample, was more comparable to observed 24-hour UIE than when predicted 24-hour Cr was from published estimates from a different population. However, currently no cutoffs exist to interpret population estimated 24-hour UIE values.

Intraindividual variation in urinary iodine concentrations: effect of adjustment on population distribution using two and three repeated spot urine collections

OBJECTIVES

To determine the effect of adjustment for intraindividual variation on estimations of urinary iodine concentrations (UIC), prevalence of iodine deficiency and population distribution of iodine status.

SETTING

Community-dwelling older adults from New South Wales, Australia.

PARTICIPANTS

84 healthy men and women aged 60-95 years were recruited prior to introduction of the mandatory iodine fortification programme.

PRIMARY AND SECONDARY OUTCOME MEASURES

UIC data were collected from three spot urine samples, each 1 week apart. Repeated measures analysis of variance were determined between-person (sb) and total (sobs) SDs. Adjusted UIC values were calculated as ((person's UIC-group mean)×(sb/sobs))+group mean, and a corrected UIC distribution was calculated.

RESULTS

The sb/sobs for using three samples and two samples were 0.83 and 0.79, respectively. Following adjustment for intraindividual variation, the proportion with UIC <50 μg/L reduced from 33% to 19%, while the proportion with UIC ≥100 μg/L changed from 21% to 17%. The 95th centile for UIC decreased from 176 to 136 μg/L. Adjustment by taking averages yielded a lesser degree of contraction in the distribution than the analysis of variance method.

CONCLUSIONS

The addition of information about intraindividual variability has potential for increasing the interpretability of UIC data collected to monitor the iodine status of a population.

The prevalence of thyroid dysfunction in elderly cardiology patients with mild excessive iodine intake in the urban area of São Paulo

OBJECTIVES

To evaluate the prevalence of thyroid dysfunction in elderly cardiac patients in an outpatient setting.

SUBJECTS AND METHODS

A total of 399 consecutive patients (268 women, age range 60-92 years) who were followed at Heart Institute were evaluated for thyroid dysfunction with serum free T4, TSH, anti-Peroxidase antibodies, urinary iodine excretion measurements and thyroid ultrasound.

RESULTS

Hyperthyroidism (overt and subclinical) was present in 29 patients (6.5%), whereas hypothyroidism (overt and subclinical) was found in 32 individuals (8.1%). Cysts were detected in 11 patients (2.8%), single nodules were detected in 102 (25.6%), and multinodular goiters were detected in 34 (8.5%). Hashimoto's thyroiditis was present in 16.8% patients, most of whom were women (83.6%). The serum TSH increased with age and was significantly higher (p= <0.01) in patients, compared to the normal control group. No significant differences in serum TSH and free T4 values were observed when patients with atrial fibrillation (AF) where compared with those without arrhythmia. The median urinary iodine levels were 210 microg/L (40-856 microg/L), and iodine levels were higher in men than in women (p<0.01). Excessive iodine intake (urinary iodine >300 microg/L) was observed in one-third of patients (30.8%).

CONCLUSIONS

Elderly patients have a higher prevalence of both hypo- and hyperthyroidism as well as thyroid nodules when compared with the general population. About one-third of the older patients had elevated urinary secretion of iodine and a higher prevalence of chronic Hashimoto's thyroiditis. It is recommended that ultrasonographic studies, tests for thyroid function and autoimmunity should be evaluated in elderly patients.

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.