Iodine Status of Canadian Children, Adolescents, and Women of Childbearing Age

Minimizing neonatal hypothyroidism induced by lithium exposure through breast milk

BACKGROUND

Lithium-induced hypothyroidism in the neonate is a growing concern for lactating mothers. Maternal hypothyroidism in the postpartum period could lead to hypothyroidism in the infant via maternal compromised thyroid hormones (likely T4) in breast milk, and lithium in breast milk could have a direct effect on the neonatal thyroid axis over lithium carbonate direct administration.

METHODS

We have studied the effects of lithium exposure on neonatal pups through two different modes of exposure: direct oral administration of lithium carbonate and indirect exposure of lithium from breast milk from dams. Furthermore, dams were supplemented with two different iodine dosages in both control and lithium-treated groups. We employed Enzyme-linked immunosorbent assay, inductively coupled plasma mass and atomic absorption spectrometry to assess hormone profiles and intrathyroidal elemental content.

RESULTS

Interestingly, lithium administered directly to pups from control mothers (average dose 900 mg/50 kg per day), did not affect their weight, thyroid hormones, blood urea, and intrathyroidal iodine content despite traces of lithium found in their blood and thyroid. The iodine pathway in the presence of lithium content in both thyroid follicular cells and lactocyte has been hypothesized. The results also demonstrate that lithium administration in lactating dams alters thyroid hormones (T4) and blood urea in both dams and pups, which could be reversed by iodine supplement. The mechanism for supplemented iodine uptake in the presence of lithium is hypothesized.

CONCLUSION

In future, supplementing iodine may be potentially useful in clinical practices to address the neonate concerns of lactating mothers and their infants either caused by prolonged lithium medication or maternal iodine deficiency.

Iodine intakes of pregnant females from Québec, Canada

BACKGROUND

Adequate maternal iodine intake is important for fetal brain development. Based on iodine intakes of non-pregnant females of reproductive age from the Canadian Health Measures Survey (2016 -2017) it can be extrapolated that most pregnant females in Canada will not meet iodine requirements without supplementation.

OBJECTIVES

To assess iodine intakes of 500 pregnant, nulliparous females from Québec, Canada and report on use of multivitamin/mineral (MVM) supplements and coverage of iodized salt.

METHODS

Duplicate spot urine samples were collected at 10.1 -14.9 weeks (T1) and 19.7 -24.9 weeks (T2) of gestation. Median urinary iodine concentrations (UIC) were compared with WHO/UNICEF/ICCIDD reference ranges. Daily iodine intakes were calculated from UIC using a formula that corrects for urine dilution using creatinine and accounts for urinary iodine excretion rate. Usual (adjusted for within-person variation) iodine intakes were estimated from duplicate daily intake measurements (T1 and T2 measures) using the National Cancer Institute method. Prevalence of inadequate or excessive intakes were determined from usual intakes by the Estimated Average Requirement (EAR) or Tolerable Upper Intake Level (UL) cut-point method, respectively.

RESULTS

Females (median: 30.1 years) were mostly white race (94.4 %), highly educated and consumed iodized salt (92 %). Median UIC at T1 (136 µg/L, IQR: 71 -230) was lower (p<0.001) than at T2 (193 µg/L, IQR: 112 -390). Almost all females used a MVM supplement (98.2 %) with 35.6 % starting supplementation preconception and 0.6 %, 28.4 %, 19.8 %, 7.2 % and 6.0 % starting 1 -2 weeks, 3 -4 weeks, 5 -8 weeks, 8 -12 weeks and > 12 weeks postconception, respectively. Almost all (99 %, 95 % CI: 98, 100) had usual iodine intakes ≥EAR and ≤UL.

CONCLUSIONS

Prevalence of inadequate or excessive usual iodine intakes was low. However, about two-thirds of females started MVM supplementation postconception and median UIC at T1 was below the adequate range of 150 -249 µg/L.

Urinary Iodine Concentration and Thyroid Hormone Metabolism in Pregnant Women and Neurodevelopment in Their Children: A Longitudinal Canadian Birth Cohort

Background/Objectives: Iodine is essential for thyroid hormone (TH) synthesis, and THs in pregnant women are critical for fetal brain development. It is unclear whether urinary iodine concentrations (UICs) are associated with thyroid parameters in pregnant women and neurodevelopment in their 3-4-year-old children. Methods: In the Canadian Maternal-Infant Research on Environmental Chemicals (MIREC) cohort, we categorized UIC adjusted for urinary creatinine (UIC/Cr) in the first two trimesters as <150, 150-500, or ≥500 µg/g. We used multivariable regression to quantify associations between UIC/Cr and thyroid parameters in maternal plasma (n = 1501), including thyroid stimulating hormone (TSH), total T4 (tT4), free T4 (fT4), thyroglobulin (Tg) and Tg antibodies (TgAb), and thyroid peroxidase antibodies (TPOAb). We defined positive thyroid autoantibodies as TgAb ≥ 4.11 or TPOAb ≥ 5.61 IU/mL. We also examined the associations between UIC/Cr with the Wechsler Preschool and Primary Scale of Intelligence (n = 503), Behavior Assessment System for Children (n = 751), and the Social Responsiveness Scale (n = 498). Results: Twenty-two percent of women had UIC/Cr < 150 and 17% ≥ 500 µg/g. UIC/Cr was not associated with TSH, tT4, or fT4. After excluding women with positive thyroid autoantibodies, those with UIC/Cr < 150 µg/g had higher tT4 compared to those with 150-500 µg/g. Compared to women with UIC/Cr 150-500 µg/g, those with UIC/Cr < 150 had higher Tg and, those with UIC/Cr ≥ 500 had less frequent positive thyroid autoantibodies. Neurodevelopmental outcomes were not associated with maternal Tg, nor did they differ for maternal UIC/Cr < 150 and ≥500 compared to 150-500 µg/g. Conclusions: In this cohort, Tg and tT4 were higher in women with UIC/Cr < 150 µg/g compared to those with UIC/Cr 150-500 µg/g. Urinary iodine in pregnant women was not associated with neurodevelopment in their 3-4-year-old children.

Iodine Status and Its Influencing Factors in Hospitalized and Healthy Preschool-Age Children

Iodine is a trace element necessary for synthesizing thyroid hormones. It is especially crucial for the neurodevelopment and intellectual development of children. Preschool-age children admitted to the hospital tend to have more fragile physical and mental health, but few studies demonstrate their iodine status. Our study aimed to investigate the iodine status of hospitalized and healthy preschool-age children and to explore the factors influencing them. From January to December 2021, 426 children aged 3-6 years were admitted to the respiratory department for pneumonia, bronchopneumonia, or bronchiectasis, but they could eat normally and were recruited as hospitalized children. Six hundred ten healthy children aged 3-6 years were included. We collected anthropometric measurements and urine samples from hospitalized and healthy preschool-age children, and iodine status was assessed through urinary iodine concentration (UIC) and urinary iodine/creatinine ratio (UI/Cr). UIC was 40.1 and 166.1 µg/L for hospitalized and healthy preschool-age children, respectively (P < 0.001). Urinary creatinine concentration (UCr) was 0.2 and 0.8 g/L for hospitalized and healthy preschool-age children, respectively (P < 0.001). UIC decreased with increasing height z-scores in hospitalized children (Spearman's rho = -0.11, P = 0.022). A significantly increased risk of UIC < 100 µg/L was found in hospitalized children (OR = 9.1 (6.8, 12.2), P < 0.001) when compared to healthy children. In conclusion, hospitalized preschool-age children are likelier to have iodine insufficiency than healthy preschool-age children, especially those with good linear growth. Measures should be implemented to ensure adequate iodine intake of preschool-age children during hospitalization to avoid affecting their intellectual and physical development. Due to lower UCr in hospitalized children, creatinine is not appropriate for assessing iodine status in hospitalized children.

Iodine Nutrition Status of Children Aged 3-13 Years in Areas with High Groundwater Iodine Content in China

BACKGROUND

Adequate iodine status is crucial for children's health and normal development. However, there is a paucity of research on the iodine status of children from areas with high groundwater iodine content.

OBJECTIVES

The objectives of this were to monitor the iodine status of children in Shandong, China (regions primarily characterized by high iodine concentrations in groundwater) and describe the factors influencing children's iodine status.

METHODS

A cross-sectional study was conducted from 2013 to 2023 on 3253 3- to 13-y-old children. We collected drinking water, spot urine, and 24-h urine samples from children to assess their iodine status [measuring drinking water iodine concentration (WIC), water iodine intake (WII), urine iodine concentration (UIC), 24-h urine iodine excretion (24-h UIE), daily iodine intake (DII), etc.], and analyzed influencing factors.

RESULTS

The median WIC for children was 183 (IQR: 70.2, 362) μg/L, and the median spot UIC was 428 (IQR: 194, 737) μg/L, surpassing the WHO cutoff (300 μg/L). Children at risk of iodine excess numbered 1750 (61.8%). Approximately 61% of iodine intake came from drinking water. Boys had significantly higher iodine intake than girls (P < 0.001). Children's age showed positive correlations with spot UIC, 24-h UIC, and 24-h UIE. There were no significant differences in 24-h UIC and 24-h UIE among children with different BMIs. The logistic regression model revealed that the risk of iodine excess was increased by boy gender, increment in age (OR: 1.05; 95% CI: 1.02, 1.08), and every 10 μg (OR: 1.04; 95% CI: 1.03, 1.04) or 50 μg (OR: 1.19; 95% CI: 1.16, 1.22) increment in WII.

CONCLUSIONS

Children in areas with high groundwater iodine content are at a risk of iodine excess. As age increases, the risk of iodine excess in children rises, with boys at a higher risk than girls.

A History of the Elimination of Iodine Deficiency Disorders in the Americas: A Dramatic Achievement and Lessons Learned

Iodine is essential for the synthesis of thyroid hormones, which regulate cell metabolism, growth, and development. Although iodine deficiency (ID) causes adverse health effects across the lifespan, it is particularly problematic in pregnancy, when it can lead to irreversible fetal brain damage. A high prevalence of severe ID, manifesting as endemic goiter and cretinism, predated the arrival of European explorers in the Americas. Early 20th century surveys showed that most countries in the Western Hemisphere had regions with a goiter prevalence >50%. In North America, the introduction of iodized salt led to the elimination of ID by the 1950s. Although most Latin American countries passed laws mandating salt iodization in the 1950s-1960s, initial programs met with limited success because laws were unenforced, monitoring was absent, and the importance of iodine nutrition was inadequately communicated. A renewed interest in ID prevention arose in the 1970s-1980s, when 3 Andean countries were the first in Latin America to implement effective salt iodization programs. Over the last 3 decades there has been a stronger political commitment to ID prevention across the region, alignment with the broader nutrition and development agenda, and a widespread recognition of optimal iodine nutrition as a fundamental human right. Currently, 92% of households in Latin America consume adequately iodized salt, and urinary iodine concentrations in schoolchildren reflect optimal iodine nutrition across the region. However, additional work remains. It is essential to ensure ongoing government commitment; to monitor population iodine status and the production, quality, and household consumption of iodized salt; and to maintain advocacy and communication strategies. Universal salt iodization programs must be harmonized with efforts to reduce salt intake for cardiovascular disease prevention. Ensuring optimal iodine nutrition in pregnant women, who may remain deficient even when intakes in schoolchildren are optimized, requires particular attention.

Supplementation practices among pregnant women and those trying to conceive: a population-representative survey in Vancouver, Canada

Dietary supplements including vitamins, minerals, and natural health products are commonly consumed by those aiming to optimize fertility and pregnancy outcomes. The aim of this survey was to describe supplementation practices among individuals who were pregnant or trying to conceive in Vancouver, Canada. An online survey was conducted among 500 individuals who were pregnant (n = 250) or trying to conceive (n = 250). Participants met a substantial proportion of vitamin and mineral recommendations through supplements alone. Exceptions included calcium, magnesium, and choline, with median (interquartile range (IQR)) supplementation doses reported by those who were pregnant and trying to conceive, respectively, of: 250 (200 and 250 mg) and 250 (200 and 250 mg), 50 (50 and 75 mg) and 50 (50 and 90 mg), and 53 (10 and 150 mg) and 55 (10 and 100 mg), as compared to perinatal recommendations of 1000 mg/day (calcium), 350 mg/day (magnesium), and 450 mg/day (choline). Conversely, median (IQR) doses of folate reported by those who were pregnant and trying to conceive, respectively, were: 1000 (780 and 1000 µg) and 1000 (800 and 1000 µg), with ∼70% overall (337/471) reporting doses ≥1000 µg (the tolerable upper intake level). Most participants (451/500; 90%) reported supplementation with a prenatal multivitamin; of these, 83% reported that supplementation occurred daily. Overall, as diet was not considered, we cannot ascertain whether recommendations for calcium, magnesium, and choline were met through the combination of supplements and foods; however, we believe that additional supplementation with choline may be required to meet recommendations in pregnancy. Excessive folate supplementation has been previously identified as a concern throughout North America; here, we provide further evidence for excessively high doses consumed via supplements.

Adjusting the Iodine Content of Iodized Salt to Meet the Recommended Intake for Females of Reproductive Age: A Simulation Study with a Reduced Sodium Scenario

BACKGROUND

The use of iodized salt is a key strategy to increase iodine intake worldwide. In many countries, including New Zealand, females of reproductive age are still at risk of being mildly iodine deficient.

OBJECTIVE

This study aimed to determine the level of iodization of salt needed to ensure that females aged 18 to 40 y have an adequate intake of iodine in 2 scenarios: current discretionary salt intake and reduced discretionary salt intake.

METHOD

Data from nonpregnant, nonlactating females aged 18 to 40 y (n = 795) who took part in the 2008/09 New Zealand Adult Nutrition Survey and completed a 24-h dietary recall were used. Iodine intake was determined from all foods except bread and discretionary salt, which are fortified with iodine. Iodine from bread and salt was estimated at different levels of salt iodization, starting at 25 mg iodine/kg salt and increasing incrementally by 5 mg/kg, and added to calculate total iodine intake. The simulation concluded when the appropriate iodine content in salt was found using the estimated average requirement (EAR) cut-point method.

RESULTS

In the 2 scenarios, current discretionary salt intake (i.e., 400 mg/d) and reduced discretionary salt intake (i.e., 304 mg/d), the iodine concentration of salt is required to be 55 mg/kg and 70 mg/kg for no more than 2% of females to have an iodine intake below the EAR of 100 μg of iodine/d, respectively. In both scenarios and at all levels of iodine concentration, no one was above the upper level of intake of iodine of 1100 μg/d.

CONCLUSIONS

This study found that females of reproductive age need to consume iodized salt at the higher end of the legislated range of 25 to 65 mg/kg. If strategies to reduce sodium intake were adopted, the range would need to increase, or iodized salt would need to be included in a wider range of staple foods.

Estimating habitual iodine intake and prevalence of inadequacy from spot urine in cross-sectional studies: a modeling analysis to determine the required sample size

BACKGROUND

The habitual/usual iodine intake and the prevalence of iodine inadequacy may be estimated from spot urinary iodine concentrations in cross-sectional studies by collecting a repeat spot urine in a subgroup of the study population and accounting for within-person variability in iodine intake. However, guidance on the required overall sample size (N) and the replicate rate (n) is lacking.

OBJECTIVES

To determine the sample size (N) and replicate rate (n) needed to estimate the prevalence of iodine inadequacy in cross-sectional studies.

METHODS

We used data from local observational studies conducted in women 17-49 y old in Switzerland (N = 308), South Africa (N = 154), and Tanzania (N = 190). All participants collected 2 spot urine samples. We calculated the iodine intake using urinary iodine concentrations and accounted for urine volume using urinary creatinine concentration. For each study population, we estimated the habitual iodine intake distribution and determined the prevalence of iodine intake below the average requirement using the Statistical Program to Assess habitual Dietary Exposure (SPADE). We used the obtained model parameters in power analyzes and estimated the prevalence of iodine inadequacy for different sample sizes (N = 400, 600, and 900) and replicate rates (n = 50, 100, 200, 400, 600, and 900).

RESULTS

The estimated prevalence (95% CI) of inadequate iodine intake was 21% (15, 28%), 5.1% (1.3, 8.7%), and 8.2% (3.4, 13%) for Swiss, South African, and Tanzanian women, respectively. An N of 400 women, with a repeated measure (n) in 100 women, achieved a satisfactory precision of the prevalence estimate in all study populations. Increasing the replicate rate (n) improved the precision more effectively than increasing the N of the study.

CONCLUSIONS

The sample size for cross-sectional studies aiming to assess the prevalence of inadequate iodine intake depend on the expected prevalence, the overall variance in intake, and the study design. However, an N of 400 participants with a repeated measure of 25% may be used as guidance when planning observational studies applying simple random sampling. This trial was registered at clinicaltrials.gov as NCT03731312.

The Prevalence and Risk Factors Associated with Iodine Deficiency in Canadian Adults

Iodine is a trace micronutrient that is critical for normal thyroid function and human health. Inadequate dietary intake is associated with cognitive impairment, infertility, growth retardation and iodine deficiency disorders in affected populations. Herein, we examined the prevalence of iodine deficiency in adults (median age of 61 years) based on the analysis of 24 h urine samples collected from 800 participants in four clinical sites across Canada in the Prospective Urban and Rural Epidemiological (PURE) study. Urinary iodide together with thiocyanate and nitrate were measured using a validated capillary electrophoresis assay. Protective/risk factors associated with iodine deficiency were identified using a binary logistic regression model, whereas daily urinary iodine concentration (24 h UIC, μg/L) and urinary iodine excretion (24 h UIE, μg/day) were compared using complementary statistical methods with covariate adjustments. Overall, our Canadian adult cohort had adequate iodine status as reflected by a median UIC of 111 μg/L with 11.9% of the population <50 μg/L categorized as having moderate to severe iodine deficiency. Iodine adequacy was also evident with a median 24 h UIE of 226 μg/day as a more robust metric of iodine status with an estimated average requirement (EAR) of 7.1% (< 95 μg/day) and a tolerable upper level (UL) of 1.8% (≥1100 μg/day) based on Canadian dietary reference intake values. Participants taking iodine supplements (OR = 0.18; p = 6.35 × 10−5), had greater 24 h urine volume (OR = 0.69; p = 4.07 × 10−4), excreted higher daily urinary sodium (OR = 0.71; p = 3.03 × 10−5), and/or were prescribed thyroxine (OR = 0.33; p = 1.20 × 10−2) had lower risk for iodine deficiency. Self-reported intake of dairy products was most strongly associated with iodine status (r = 0.24; p = 2.38 × 10−9) after excluding for iodine supplementation and T4 use. Participants residing in Quebec City (OR = 2.58; p = 1.74 × 10−4) and Vancouver (OR = 2.54; p = 3.57 × 10−4) were more susceptible to iodine deficiency than Hamilton or Ottawa. Also, greater exposure to abundant iodine uptake inhibitors from tobacco smoking and intake of specific goitrogenic foods corresponded to elevated urinary thiocyanate and nitrate, which were found for residents from Quebec City as compared to other clinical sites. Recent public health policies that advocate for salt restriction and lower dairy intake may inadvertently reduce iodine nutrition of Canadians, and further exacerbate regional variations in iodine deficiency risk.

Iodine Status of Mother-Infant Dyads from Montréal, Canada: Secondary Analyses of a Vitamin D Supplementation Trial in Breastfed Infants

BACKGROUND

Most pregnant or lactating women in Canada will not meet iodine requirements without iodine supplementation.

OBJECTIVES

To assess the iodine status of 132 mother-infant pairs based on secondary analyses of a vitamin D supplementation trial in breastfed infants from Montréal, Canada.

METHODS

Maternal iodine status was assessed using the breastmilk iodine concentration (BMIC). Singleton, term-born infants were studied from 1-36 months of age. Usual (adjusted for within-person variation) iodine intakes were estimated from urinary iodine and creatinine concentrations. Iodine status was assessed using median urinary iodine concentrations (UICs) and by estimating inadequate intakes by the cut-point method using a proposed Estimated Average Requirement for infants 0-6 months of age (72 μg/d).

RESULTS

At 1, 3, and 6 months of age, 70%, 63%, and 3% of infants, respectively, were exclusively breastfed. From 1-36 months of age (n = 82-129), the median UICs were ≥100 μg/L (range, 246-403 μg/L), which is the cutoff for adequate intakes set by the WHO for children <2 years. Almost all (98%-99%) infants at 1 and 2 months, 2 and 3 months, and 3 and 6 months of age had usual creatinine-adjusted iodine intakes ≥ 72 μg/d. The median BMIC was higher (P < 0.001) at 1 month compared to 6 months of lactation [1 month, 198 μg/kg (IQR, 124-274; n = 105) and 6 months, 109 μg/kg (IQR, 67-168; n = 78)]. At 1 and 6 months, 96% and 79% of mothers, respectively, had a BMIC ≥ 60 μg/kg, the lower limit of a normal reference range. The percentages of mothers that used a multivitamin-mineral (MVM) supplement containing iodine were 90% in pregnancy and 79% and 59% at 1 and 6 months of lactation, respectively.

CONCLUSIONS

The iodine status of infants was adequate throughout infancy. These results support a recommendation that all women who could become pregnant, who are pregnant, or who are breastfeeding take a daily MVM supplement containing iodine.