Adverse effects on thyroid of Chinese children exposed to long-term iodine excess: optimal and safe Tolerable Upper Intake Levels of iodine for 7- to 14-y-old children

An Iodine Balance Study in Chinese School-age Children

CONTEXT

Few iodine balance studies have been conducted in school-age children.

OBJECTIVE

This study aimed to conduct an iodine balance study in school-age children.

METHODS

We measured daily iodine intake, excretion, and retention for 3 consecutive days without any dietary interventions in school-age children. Linear mixed-effects models were used to fit the relationship between total iodine intake and iodine retention.

RESULTS

29 children aged 7-12 years (mean age 10.2 ± 1.4 years) with normal thyroid function and thyroid volume were recruited. The 0 balance value (iodine intake = iodine excretion, iodine retention = 0 μg/day) shifted with iodine intake in an iodine sufficient population. The 0 balance value for school-age children with an iodine intake of 235 (133, 401) μg/day is 164 μg/day. Children aged 7-12 years with iodine intake >400 μg/day were almost all in a positive iodine state.

CONCLUSION

An iodine intake of 235 (133, 401) μg/day for children aged 7-10 years achieved a 0 balance value of 164 μg/day. Long-term iodine intake of >400 μg/day is not recommended.

Associations between urinary iodine concentration and the prevalence of metabolic disorders: a cross-sectional study

Background

Few studies have examined the role of iodine in extrathyroidal function. Recent research has shown an association between iodine and metabolic syndromes (MetS) in Chinese and Korean populations, but the link in the American participants remains unknown.

Purpose

This study aimed to examine the relationship between iodine status and metabolic disorders, including components associated with metabolic syndrome, hypertension, hyperglycemia, central obesity, triglyceride abnormalities, and low HDL.

Methods

The study included 11,545 adults aged ≥ 18 years from the US National Health and Nutrition Examination Survey (2007-2018). Participants were divided into four groups based on their iodine nutritional status(ug/L), as recommended by the World Health Organization: low UIC, < 100; normal UIC, 100-299; high UIC, 300-399; and very high, ≥ 400. The Odds ratio (OR) for MetS basing the UIC group was estimated using logistic regression models for our overall population and subgroups.

Results

Iodine status was positively associated with the prevalence of MetS in US adults. The risk of MetS was significantly higher in those with high UIC than in those with normal UIC [OR: 1.25; 95% confidence intervals (CI),1.016-1.539; p = 0.035). The risk of MetS was lower in the low UIC group (OR,0.82; 95% CI: 0.708-0.946; p = 0.007). There was a significant nonlinear trend between UIC and the risk of MetS, diabetes, and obesity in overall participants. Participants with high UIC had significantly increased TG elevation (OR, 1.24; 95% CI: 1.002-1.533; P = 0.048) and participants with very high UIC had significantly decreased risk of diabetes (OR, 0.83; 95% CI: 0.731-0.945, p = 0.005). Moreover, subgroup analysis revealed an interaction between UIC and MetS in participants aged < 60 years and ≥ 60 years, and no association between UIC and MetS in older participants aged ≥ 60 years.

Conclusion

Our study validated the relationship between UIC and MetS and their components in US adults. This association may provide further dietary control strategies for the management of patients with metabolic disorders.

Adverse Effects on the Thyroid of Chinese Pregnant Women Exposed to Long-Term Iodine Excess: Optimal and Safe Tolerable Upper Intake Levels of Iodine

Ensuring optimal iodine nutrition in pregnant women is a global public health concern. However, there is no direct data on safe tolerable upper intake levels (ULs) for pregnant women. A cross-sectional study was performed to determine the ULs of pregnant women. A total of 744 pregnant women were enrolled in this study. The median (IQR) urinary iodine concentration (UIC) in pregnant women was 150.2 (87.6, 268.0) μg/L, and the urinary iodine excretion (UIE) over 24 h was 204.2 (116.0, 387.0) μg/day. Compared with those with a UIE figure of between 150–250 μg/day, the reference group, the prevalence of thyroid dysfunction was 5.7 times higher (95%CI: 1.7, 19.2) in pregnant women with a UIE figure of between 450–550 μg/day, and 3.9 times higher (95%CI: 1.5, 10.3) in pregnant women with a UIE figure of ≥550 μg/day. Compared with an estimated iodine intake (EII) of between 100–200 μg/day, the reference group, the prevalence of thyroid dysfunction was 4.3 times higher (95%CI: 1.3, 14.4) in pregnant women with a UIE figure of between 500–600 μg/day, and 3.6 times higher (95%CI: 1.5, 8.9) in pregnant women with UIE of ≥600 μg/day. In general, our cross-sectional study found that excessive iodine intake during pregnancy appears to directly increase the risk of thyroid dysfunction. Avoiding chronic iodine intakes of 500 μg/day or higher or having a UIE figure of ≥450 μg/day is recommended for pregnant women in China.

Relationship of iodine excess with thyroid function in 6-year-old children living in an iodine-replete area

BACKGROUND

Adequate iodine intake is essential for growing children, as both deficient and excessive iodine status can result in thyroid dysfunction. We investigated the iodine status and its association with thyroid function in 6-year-old children from South Korea.

METHODS

A total of 439 children aged 6 (231 boys and 208 girls) were investigated from the Environment and Development of Children cohort study. The thyroid function test included free thyroxine (FT4), total triiodothyronine (T3), and thyroid-stimulating hormone (TSH). Urine iodine status was evaluated using urine iodine concentration (UIC) in morning spot urine and categorized into iodine deficient (< 100 μg/L), adequate (100-199 μg/L), more than adequate (200-299 μg/L), mild excessive (300-999 μg/L), and severe excessive (≥ 1000 μg/L) groups. The estimated 24-hour urinary iodine excretion (24h-UIE) was also calculated.

RESULTS

The median TSH level was 2.3 μIU/mL, with subclinical hypothyroidism detected in 4.3% of patients without sex differences. The median UIC was 606.2 μg/L, with higher levels in boys (684 μg/L vs. 545 μg/L, p = 0.021) than girls. Iodine status was categorized as deficient (n = 19, 4.3%), adequate (n = 42, 9.6%), more than adequate (n = 54, 12.3%), mild excessive (n = 170, 38.7%), or severe excessive (n = 154, 35.1%). After adjusting for age, sex, birth weight, gestational age, body mass index z-score, and family history, both the mild and severe excess groups showed lower FT4 (β = - 0.04, p = 0.032 for mild excess; β = - 0.04, p = 0.042 for severe excess) and T3 levels (β = - 8.12, p = 0.009 for mild excess; β = - 9.08, p = 0.004 for severe excess) compared to the adequate group. Log-transformed estimated 24h-UIE showed a positive association with log-transformed TSH levels (β = 0.04, p = 0.046).

CONCLUSION

Excess iodine was prevalent (73.8%) in 6-year-old Korean children. Excess iodine was associated with a decrease in FT4 or T3 levels and an increase in TSH levels. The longitudinal effects of iodine excess on later thyroid function and health outcomes require further investigation.

Relationship between water iodine and children's goiters

Excessive iodine can lead to goiters. However, the relationship between the water iodine concentration (WIC) and goiter rate (GR) is unclear. This study aims to explore the factors that influence children's GR in areas with high WIC and analyse the threshold value of the GR increase associated with the WIC. According to the monitoring of the areas with high WIC in China in 2018-2020, a total of 54 050 children in eight high water iodine provinces were chosen. Drinking water, urine and edible salt samples of children were collected. The thyroid volume (Tvol) was measured. A generalised additive model (GAM) was used to analyse the relationship between the WIC and GR in children. Among the 54 050 children in areas with high WIC, the overall GR was 3·34 %, the median of water iodine concentration was 127·0 µg/l, the median of urinary iodine concentration was 318 µg/l and the non-iodised salt coverage rate (NISCR) was 63·51 %. According to the GAM analysis results, water iodine and urinary iodine are factors that influence the Tvol and GR, while the NISCR affects only the GR. When the WIC was more than 420 µg/l or the urinary iodine concentration was more than 800 µg/l, the GR increased rapidly. When the NISCR reached more than 85 %, the GR was the lowest. Thus, in areas with high WIC, WIC more than 420 µg/l may increase the risk of goiter, and the NISCR should be increased to over 85 % to avoid goiters in children.

Impact of urinary iodine concentration on blood glucose levels and blood pressure: a nationwide population-based study

PURPOSE

Iodine is a vital trace element for systemic metabolic control as well as thyroid hormone synthesis. Though iodine has significant antioxidant and anti-inflammatory effects, reports on its effects on metabolic disorders are limited and inconsistent.

METHODS

Impact of urinary iodine concentrations (UICs) on fasting blood glucose (FBG) levels and blood pressure (BP) in the general Korean population was evaluated adjusting for covariates including thyrotropin level and presence of thyroid diseases.

RESULTS

The median UIC was 302.3 μg/L in all participants and was significantly lower in those with dysglycemia (303.6 μg/L in normal participants, 285.1 μg/L in participants with FBG levels of 100-125 mg/dL, and 261.8 μg/L in participants with FBG levels ≥ 126 mg/dL; p = 0.002). Similarly, the UIC was lower in participants with higher BP (311.6 μg/L in normal participants, 288.7 μg/L in prehypertensive participants, and 265.8 μg/L in hypertensive participants; p < 0.001). The multiple linear regression model showed a negative correlation between the UIC and FBG levels (p = 0.002), and the UIC and systolic BP (p < 0.001). One standard deviation increase in the UIC showed odds ratios of 0.84 (95% confidence interval [CI] = 0.73-0.98) for elevated FBG levels (≥ 100 mg/dL) and 0.94 (95% CI = 0.88-0.99) for elevated SBP (≥ 120 mm Hg) after full adjustment.

CONCLUSION

Higher UICs were associated with lower FBG and BP levels, independent of thyroid function and other confounding factors in Korea, an iodine-replete country.

Comparative Analysis of Five Correction Methods for Thyroid Volume by Ultrasound and Their Recommended Reference Values in Chinese Children Aged 8-10 Years

Considering the influence of body's growth and development on thyroid volume (TVOL), whether five existed corrected methods could be applied to correct TVOL remains unclear, in terms of Chinese children's increased growth and development trends. This study aimed to compare the applicability of five correction methods for TVOL: Body Surface Area corrected Volume (BSAV), Body Mass Indicator corrected Volume (BMIV), Weight and Height corrected Volume Indicator (WHVI), Height corrected Volume Indicator 1 (HVI1) and Height corrected Volume Indicator 2 (HVI2); to establish the reference values for correction methods. The data of Iodine Nutrition and Thyroid Function Survey was used to analyse the differences in TVOL between normal and abnormal thyroid function children. Data of National Iodine Deficiency Disorders Survey were used to compare five correction methods and to establish their reference values. The median urinary iodine concentration of children surveyed were 256.1μg/L in 2009 and 192.6μg/L in 2019, respectively. No significant difference was found in TVOL and thyroid goitre rate between children with normal and abnormal thyroid function. In the determination of goitre, HVI1, HVI2, BSAV and BMIV all showed high agreement with TVOL, while the area under the ROC curve (AUC) of WHVI was relatively low for children aged 8(AUC=0.8993) and 9(AUC=0.8866). Most differences of TVOL between light and heavy weight, short and tall height children can be eliminated by BSAV correction. BSAV was the best method of TVOL correction in this research. Reference values were established for corrected thyroid volumes in Chinese children aged 8-10 years by sex.

A new gold nanoflower sol SERS method for trace iodine ion based on catalytic amplification

As one of the essential trace elements in metabolism, iodine is crucial to maintain the normal physiological functions. Therefore, based on health and environmental protection, it is very important to realize sensitive detection of iodide ion. Herein, we developed a simple, rapid and sensitive method for the determination of iodide ion. Trypsin was used as an ideal template for the synthesis of gold nanoflower sol (AuNFs) with anisotropic surface structure and good stability. It exhibits highly active surface enhanced Raman scattering (SERS) effect and can be used as facile SERS sol substrate. The TMBox generated by the catalytic oxidation reaction of TMB-chloramine T-iodide ion is used as the SERS probe. The enhanced SERS signal intensity is linearly related to the iodide ion with high sensitivity. In addition, TMB has fluorescence effect, and the colored TMBox can produce RRS signal due to polymerization. Based on this, a quad-mode detection method of SERS, RRS, fluorescence and colorimetry for quantitative detection of trace iodide ions was established, and this method can be applied to the detection of iodide ions in natural water and drinking water.

Effects of long-term excessive iodine intake on blood lipids in Chinese adults: a cross-sectional study

OBJECTIVE

The aim of this study was to evaluate the effects of long-term excessive iodine intake on blood lipids in adults.

METHODS

Three counties from Dezhou city and Liaocheng city in the Shandong province of China were selected as survey locations. Three to five villages were selected from each county and then categorized by the iodine concentration detected in the groundwater into Low (<10 µg/L), Medium (10-150 µg/L), High (150-300 µg/L), and Excessive (>300 µg/L) groups. A self-reported questionnaire was completed by each subject to provide demographic characteristics. Body height, weight, and blood pressure were recorded by trained staff. Blood lipids were measured.

RESULTS

A total of 2156 subjects were recruited for the final analysis. The serum triglyceride (TRIG) was significantly higher in the Excessive group than in the other three groups (P < 0.05). Total cholesterol (TCHOL) and low-density lipoprotein-cholesterol (LDL-C) showed downward trends with the increases in the water iodine concentration. A statistical significance of the crude correlation coefficient was detected between the water iodine concentration and the TRIG, TCHOL, or LDL-C (P < 0.05). A significant correlation was also noted between the water iodine concentration and TCHOL or LDL-C after adjustment for covariates. High iodine concentration was a significant protective factor for TCHOL and LDL-C in adults, whereas elevated BMI and advancing age were risk factors for both variables.

CONCLUSION

An association was identified between iodine excess and low TCHOL or LDL-C. In areas with excessive iodine, iodine intake should be considered in studies examining the factors that influence blood lipids.

Saliva Iodine Concentration in Children and Its Association with Iodine Status and Thyroid Function

CONTEXT

The effectiveness of saliva iodine concentration (SIC) in evaluating iodine status in children is not clear.

OBJECTIVE

We aimed to explore associations between SIC and assessed indicators of iodine status and thyroid function.

DESIGN

Cross-sectional study.

SETTING

Primary schools in Shandong, China.

PARTICIPANTS

Local children aged 8 to 13 years with no known thyroid disease were recruited to this study.

MAIN OUTCOME MEASURES

Blood, saliva, and urine samples were collected to evaluate thyroid function and iodine status.

RESULTS

SIC positively correlated with spot urinary iodine concentration (r = 0.29, P < 0.0001), 24-hour urinary iodine concentration (r = 0.35, P < 0.0001), and 24-hour urinary iodine excretion (r = 0.40, P < 0.0001). The prevalence of thyroid nodules (TN) and goiter showed an upward trend with SIC quantiles (P for trend < 0.05). Children with SIC <105 μg/L had a higher risk of insufficient iodine status (OR = 4.18; 95% CI, 2.67-6.56) compared with those with higher SIC. Those having SIC >273 μg/L were associated with greater risks of TN (OR = 2.70; 95% CI, 1.38-5.26) and excessive iodine status (OR = 18.56; 95% CI, 5.66-60.91) than those with lower SIC values.

CONCLUSIONS

There is a good correlation between SIC and urinary iodine concentrations. It is of significant reference value for the diagnosis of iodine deficiency with SIC of less than 105 μg/L and for the diagnosis of iodine excess and TN with SIC of more than 273 μg/L. Given the sanitary nature and convenience of saliva iodine collection, SIC is highly recommended as a good biomarker of recent iodine status in school-aged children.

The relationships between thyroid-stimulating hormone and/or dopamine levels in peripheral blood and IQ in children with different urinary iodine concentrations

Environmental iodine deficiency or excess can lead to inappropriate iodine nutrition in the population. Little research has been performed to determine whether changes in thyroid-stimulating hormone (TSH) and/or dopamine (DA) concentrations in peripheral blood are involved in intellectual impairment caused by inappropriate iodine nutrition. 498 children aged 7-12 from areas with different water iodine concentrations were included in the study. Children's intelligence and levels of urinary iodine and fluoride, TSH, free triiodothyronine (FT₃), free thyroxine (FT₄), and DA were evaluated. The relationship between TSH and/or DA levels and intelligence quotient (IQ) in all participants and in the population with different urinary iodine concentrations (UIC) was evaluated by multivariate regression analysis. The proportion of people with low average and lower intelligence in UIC ≥ 300 μg/L group was significantly higher than that in control group but only a positive correlation was found between DA and IQ in the population with UIC < 100 μg/L (bootstrapped estimation P = 0.032). TSH and/or DA in peripheral blood may be not involved in the progressive decline in intelligence caused by iodine excess but DA had positive correlation with intelligence in iodine deficiency group, and no relationship between TSH concentration and IQ was found in the general population or in different UIC groups.

Iodine nutritional status of pregnant women in an urban area of northern Taiwan in 2018

Pregnant women are considered as one of the most vulnerable groups for iodine deficiency. The Nutrition and Health Survey in Taiwan 2013 revealed that the median urinary iodine concentration (UIC) of non-pregnant women of child-bearing age of 15-44 years was 124 μg/L, which was adequate in general, but insufficient according to pregnancy criteria. The aim of this study was to determine the iodine nutritional status of pregnant women in an urban area of Northern Taiwan. A hospital-based cross-sectional survey was conducted in Taipei Veterans General Hospital. Random spot urine samples were collected from January to October, 2018 and UIC was determined by inductively coupled plasma mass-spectrometry. A food frequency questionnaire was also delivered to the participants. The overall median UIC was 225.3 μg/L (IQR: 109.1-514.2 μg/L) for 257 pregnant women ranging from 21-47 years-old. The distribution of UIC was as follows: 35.4% with UIC <150 μg/L, 17.1% with UIC within 150-249 μg/L, 21.8% with UIC within 250-499 μg/L, and 25.7% with UIC ≥500 μg/L. The use of prenatal multivitamin was very common among the participants: 79.4% (n = 204) took multivitamin either every day or less frequently, with 52.5% (n = 135) taking one pill every day, and only 20.6% (n = 53) never took multivitamin during their pregnancy. Other commonly consumed iodine-containing foods were dairy products and fish. Our results indicate that the iodine status in the studied women is adequate. However, efforts are still needed to avoid iodine deficiency as well as iodine excess.

Effects of Excessive Iodine Intake on Blood Glucose, Blood Pressure, and Blood Lipids in Adults

To understand the effects of excess iodine intake on blood glucose, blood pressure, and blood lipids in adults. We selected three villages from Shanxi Province to conduct cross-sectional survey: Maxi [median water iodine concentration (MWIC) 6.3 μg/L, median urinary iodine concentration (MUIC) 126.6 μg/L, 320 adults]; Xiwenzhuang (MWIC 79.8 μg/L, MUIC 221.2 μg/L, 264 adults); and Gaoche (MWIC 506.0 μg/L, MUIC 421.3 μg/L, 241 adults). According to the urinary iodine levels in adults, the three villages were defined as iodine-adequate, iodine-sufficient, and iodine-excess. Urinary iodine, water iodine, thyroid function, blood glucose, blood pressure, and blood lipids were measured. Compared with the iodine-adequate area, blood glucose and systolic and diastolic pressure of adults in iodine-sufficient and iodine-excess areas increased and high-density lipoprotein-cholesterol decreased (all P < 0.001). Urinary iodine, thyroid-stimulating hormone, and free thyroxine have a nonlinear correlation with blood glucose (R² = 0.8174, 0.8264, and 0.8520, respectively). Excessive iodine intake may result in elevated blood glucose and blood pressure and has some influence on blood lipids, and may increase the risk of hypertension and diabetes.

Optimal Assessment and Quantification of Iodine Nutrition in Pregnancy and Lactation: Laboratory and Clinical Methods, Controversies and Future Directions

Iodine intake must be boosted during pregnancy to meet the demands for increased production and placental transfer of thyroid hormone essential for optimal foetal development. Failure to meet this challenge results in irreversible brain damage, manifested in severity from neurological cretinism to minor or subtle deficits of intelligence and behavioural disorders. Attention is now being focused on explaining observational studies of an association between insufficient iodine intake during pregnancy and mild degrees of intellectual impairment in the offspring and confirming a cause and effect relationship with impaired maternal thyroid function. The current qualitative categorisation of iodine deficiency into mild, moderate and severe by the measurement of the median urinary iodine concentration (MUIC) in a population of school-age children, as a proxy measure of dietary iodine intake, is inappropriate for defining the degree or severity of gestational iodine deficiency and needs to be replaced. This review examines progress in analytical techniques for the measurement of urinary iodine concentration and the application of this technology to epidemiological studies of iodine deficiency with a focus on gestational iodine deficiency. We recommend that more precise definitions and measurements of gestational iodine deficiency, beyond a spot UIC, need to be developed. We review the evidence for hypothyroxinaemia as the cause of intrauterine foetal brain damage in gestational iodine deficiency and discuss the many unanswered questions, from which we propose that further clinical studies need to be designed to address the pathogenesis of neurodevelopmental impairments in the foetus and infant. Agreement on the testing instruments and standardization of processes and procedures for Intelligence Quotient (IQ) and psychomotor tests needs to be reached by investigators, so that valid comparisons can be made among studies of gestational iodine deficiency and neurocognitive outcomes. Finally, the timing, safety and the efficacy of prophylactic iodine supplementation for pregnant and lactating women needs to be established and confirmation that excess intake of iodine during pregnancy is to be avoided.

Iodine Nutrition and Thyroid Function in Pregnant Women Exposed to Different Iodine Sources

Pregnant women are more vulnerable to iodine deficiency and iodine excess. The study aimed to assess the changes in iodine nutrition and thyroid function of pregnant women exposed to different iodine sources resulting in various iodine intakes during pregnancy. From 2016 to 2017, 2004 healthy pregnant women aged 20-35 years from Shandong and Tianjin, China, were enrolled. Urinary iodine concentration (UIC), drinking water iodine content (WIC), thyroid-stimulating hormone (TSH), free triiodothyronine (FT3), free thyroid hormone (FT4), thyroglobulin (Tg), serum thyroid peroxidase antibody (TPOAb), and thyroglobulin antibody (TgAb) were measured. Pregnant women in both Shandong and Tianjin were iodine sufficient, but the median UIC in pregnant women was significantly higher in Shandong (244 μg/L) than that in Tianjin (159 μg/L). No differences were found in UIC over the course of gestation in Shandong. In Tianjin, the UIC decreased during 13-24 weeks and stabilized thereafter. Compared with Tianjin, TSH levels were higher and FT3 and FT4 levels were lower in Shandong. Both FT3 and FT4 significantly decreased during pregnancy in Shandong and Tianjin. TSH and Tg increased over the course of gestation in both Shandong and Tianjin. The iodine status of pregnant women in Tianjin and Shandong were sufficient, but different changing patterns in UIC and thyroid function during pregnancy were presented. More attention should be focused on iodine nutrition of pregnant women, even in iodine-sufficient areas.

Excess iodine intake: sources, assessment, and effects on thyroid function

Iodine is essential for thyroid hormone synthesis. High iodine intakes are well tolerated by most healthy individuals, but in some people, excess iodine intakes may precipitate hyperthyroidism, hypothyroidism, goiter, and/or thyroid autoimmunity. Individuals with preexisting thyroid disease or those previously exposed to iodine deficiency may be more susceptible to thyroid disorders due to an increase in iodine intake, in some cases at intakes only slightly above physiological needs. Thyroid dysfunction due to excess iodine intake is usually mild and transient, but iodine-induced hyperthyroidism can be life-threatening in some individuals. At the population level, excess iodine intakes may arise from consumption of overiodized salt, drinking water, animal milk rich in iodine, certain seaweeds, iodine-containing dietary supplements, and from a combination of these sources. The median urinary iodine concentration (UIC) of a population reflects the total iodine intake from all sources and can accurately identify populations with excessive iodine intakes. Our review describes the association between excess iodine intake and thyroid function. We outline potential sources of excess iodine intake and the physiological responses and consequences of excess iodine intakes. We provide guidance on choice of biomarkers to assess iodine intake, with an emphasis on the UIC and thyroglobulin.

Shift of Reference Values for Thyroid Volume by Ultrasound in 8- to 13-Year-Olds with Sufficient Iodine Intake in China

BACKGROUND

The iodine nutritional status of the Chinese population has been greatly improved in recent years. Therefore, the reference values for thyroid volume (Tvol) in children with sufficient iodine intake need to be updated. The study aimed to update the reference values for Tvol in children with sufficient iodine intake in order to define goiter in the context of sustained iodine sufficiency.

METHODS

A cross-sectional study was conducted in children with sufficient iodine intake in China. Twice-repeated 24-hour urine samples were collected from each child to estimate habitual daily iodine intake. Serum thyroid function tests were measured. Tvol was assessed by ultrasound. From the sample of euthyroid children with sufficient iodine intakes, the 50th and 97th percentiles for Tvol by age and body surface area (BSA) were calculated using quantile regression.

RESULTS

A total of 679 children aged 8-13 years with sufficient iodine intake (188 μg/day [145-235 μg/day]) were included in the analysis. The mean Tvol of the children was 4.1 ± 1.6 mL, and no differences were found between boys and girls in any age or BSA group. Quantile regression models demonstrated that BSA was a strong positive predictor of Tvol (p < 0.0001), while age only had a significant effect on median Tvol (p = 0.013). Sex was not a significant predictor of Tvol in children.

CONCLUSIONS

The reference values for Tvol in Chinese children have been updated. This study indicates that the upper limit of (97th percentile) Tvol was dependent on BSA, while the median Tvol was determined by both age and BSA.

Excess micronutrient intake: defining toxic effects and upper limits in vulnerable populations

Excessive micronutrient intake causes a variety of adverse health effects, depending on dose and duration. The risk of excess intake carries significant implications for micronutrient delivery interventions, particularly when such programs are overlapping. To minimize risk and provide public health guidance, several countries and the Food and Agriculture Organization of the United Nations/World Health Organization have set upper intake levels (ULs) for various life-stage populations using the risk assessment framework. However, there is a lack of international consensus on the actual ULs due to variability in application of this framework and a scarcity of evidence from which to draw upon, especially for children. Often ULs for children are established through a downward weight-based extrapolation from adult ULs, which is not always appropriate. The published ULs of nine organizations are compared, recent population nutrient intake evidence is presented, and the toxic effects of key minerals and vitamins are reviewed. Finally, the evidence for toxicity and setting of ULs for each nutrient is discussed including a comment on our degree of confidence in the strength of existing individual ULs. Challenges with risk assessment and opportunities for strengthening the definition of ULs are discussed.

Provision of micronutrients in coexisting public health programs and risk of excessive intake: regulatory considerations

Countries around the world have been implementing public health interventions to provide vitamins and minerals. There is a concern that the cumulative micronutrient contribution of coexisting programs, when targeting the same population, may exceed their safe levels of intake, thus potentially challenging the primum non nocere principle. We assessed the regulatory framework of such interventions and determined qualitatively whether there were provisions in the regulations that called for coordination among programs to ensure their innocuousness. Country cases from various WHO regions were selected for the study: (1) the Americas: Chile, Costa Rica, and Guatemala; (2) Africa: Malawi, Uganda, and Zambia; (3) South Asia: Bangladesh; and (4) the Western Pacific Region: China and the Philippines. We did not identify any provisions in the existing regulations requiring coordination mechanisms among interventions. However, in some countries, governments have established national micronutrient fortification commissions or alliances aimed to foster interprogram coordination. Their focus, however, has been mostly on the efficacy of the programs and less on their safety. A regulatory framework for coexisting micronutrient interventions should be comprehensive, accounting for all micronutrient sources and including regulatory provisions for coordination among programs.