Temporal patterns in perchlorate, thiocyanate, and iodide excretion in human milk

Associations of Trimester-Specific Exposure to Perchlorate, Thiocyanate, and Nitrate with Childhood Neurodevelopment: A Birth Cohort Study in China

Studies about the impacts of maternal exposure to perchlorate, thiocyanate, and nitrate on offspring neurodevelopment are scarce. Based on a birth cohort in China, 1,028 mothers provided urine samples at three trimesters for determination of the three target analytes, and their offspring neurodevelopment was evaluated at 2 years old. Associations of maternal exposure to the three chemicals with offspring neurodevelopment were estimated using three statistical methods. Trimester-specific analyses using generalized estimating equation models showed that double increment of thiocyanate and nitrate during the first trimester was associated with 1.56 (95% CI: -2.82, -0.30) and 1.22 (-2.40, -0.03) point decreases in the offspring mental development index (MDI), respectively. Weighted quantile sum (WQS) regression analyses showed that the mixture exposure at the first and second trimesters was negatively associated with the offspring MDI (β = -2.39, 95% CI: -3.85, -0.93; β = -1.75, 95% CI: -3.04, -0.47, respectively) and thiocyanate contributed the most to the association (65.0 and 91.6%, respectively). Bayesian kernel machine regression analyses suggested an inverted U-shape relationship of maternal urinary thiocyanate with the offspring MDI. These findings suggested that prenatal exposure to the three chemicals (at current levels), especially thiocyanate and nitrate, may impair neurodevelopment. Early pregnancy seems to be the sensitive window.

Environmental exposure to perchlorate, nitrate and thiocyanate, and thyroid function in Chinese adults: A community-based cross-sectional study

BACKGROUND

Evidence on environmental exposure to perchlorate, nitrate, and thiocyanate, three thyroidal sodium iodine symporter (NIS) inhibitors, and thyroid function in the Chinese population remains limited.

OBJECTIVE

To investigate the associations of environmental exposure to perchlorate, nitrate, and thiocyanate with markers of thyroid function in Chinese adults.

METHODS

A total of 2441 non-pregnant adults (mean age 50.4 years and 39.1% male) with a median urinary iodine of 180.1 μg/L from four communities in Shenzhen were included in this cross-sectional study. Urinary perchlorate, nitrate, thiocyanate, and thyroid profiles, including serum free thyroxine (FT4), total thyroxine (TT4), free triiodothyronine (FT3), total triiodothyronine (TT3), and thyroid stimulating hormone (TSH), were measured. Generalized linear model was applied to investigate the single-analyte associations. Weighted quantile sum (WQS) regression and Bayesian kernel machine regression (BKMR) models were used to examine the association between the co-occurrence of three anions and thyroid profile.

RESULTS

The median levels of urinary perchlorate, nitrate, and thiocyanate were 5.8 μg/g, 76.4 mg/g, and 274.1 μg/g, respectively. After adjusting for confounders, higher urinary perchlorate was associated with lower serum FT4, TT4, and TT3, and higher serum FT3 and TSH (all P < 0.05). Comparing extreme tertiles, subjects in the highest nitrate tertile had marginally elevated TT3 (β: 0.02, 95% CI: 0.00-0.04). Each 1-unit increase in log-transformed urinary thiocyanate was associated with a 0.04 (95% CI: 0.02-0.06) pmol/L decrease in serum FT3. The WQS indices were inversely associated with serum FT4, TT4, and FT3 (all P < 0.05). In the BKMR model, the mixture of three anions was inversely associated with serum FT4, TT4, and FT3.

CONCLUSIONS

Our study provides evidence that individual and combined environmental exposure to perchlorate, nitrate, and thiocyanate are associated with significant changes in thyroid function markers in the Chinese population with adequate iodine intake.

Exposure to perchlorate, nitrate, and thiocyanate and the prevalence of abdominal aortic calcification

Perchlorate, nitrate, and thiocyanate are reported to affect human health. However, it is unclear about the associations between exposure to these chemicals and abdominal aortic calcification (AAC). A total of 959 individuals were included in a large representative survey. Urinary levels of perchlorate, nitrate, and thiocyanate were measured by ion chromatography coupled with electrospray tandem mass spectrometry. AAC was diagnosed based on dual-energy X-ray absorptiometry (DXA). There were 276 (28.8%) cases of AAC among the participants. The level of urinary nitrate was significantly lower in AAC patients compared with non-AAC patients (36.4 mg/L [20.6, 59.5] vs. 42.4 [23.8, 68.3]; P = 0.013). In multivariable-adjusted logistic regression models, urinary nitrate was associated with the prevalence of AAC. Compared with the lowest quartile, the odds ratios (95% confidence intervals) across increasing quartiles were 1.06 (0.69-1.61; P = 0.799), 0.64 (0.41-1.00; P = 0.049) and 0.74 (0.47-1.15; P = 0.180). Restricted cubic splines suggested that urinary nitrate ranging between 43.7 and 115.4 mg/L was associated with a lower risk of AAC. Moderate exposure to nitrate was associated with a lower risk of AAC.

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

BACKGROUND

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

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Characteristics and predictors of breast milk iodine in exclusively breastfed infants: Results from a repeated-measures study of iodine metabolism

Background

The iodine supply of exclusively breastfed infants entirely depends upon breast milk. Changes in breast milk iodine affect infants’ iodine nutritional status. This study aimed to comprehensively assess the characteristics and predictors of breast milk iodine concentration (BMIC).

Materials and methods

This 7-day iodine metabolism experiment was conducted in 25 exclusively breastfed mother-infant pairs. The duplicate portion method was used to measure the mother’s daily iodine intake from foods and water, and maternal 24-h urine excretion was assessed. We recorded the number of breastfeeds per mother per day and collected breast milk samples before and after each feeding.

Results

The median [quartile (Q)1–Q3 range] of BMIC was 115 (86.7, 172) μg/L. The BMIC before breastfeeding was generally higher than that after breastfeeding. Time-sequential analysis found that morning BMIC was most highly correlated with the prior day’s iodine intake. Breast milk samples taken in the afternoon or after midnight are closer to the median level of BMIC throughout the day. The number of breast milk samples needed to estimate the iodine level with 95% CI within precision ranges of ± 20% was 83 for a population, 9 for an individual, and 2 for an individual’s single day. Maternal total iodine intake (TII) and urine iodine were significantly associated with BMIC. 24-h urinary iodine excretion (24-h UIE) was found to be the best predictive indicator for the BMIC (β = 0.71, 95% CI: 0.64, 0.79).

Conclusion

BMIC is a constantly changing indicator and trended downward during each breastfeeding. Breast milk samples taken in the afternoon or after midnight are most representative. BMIC was significantly associated with recent iodine intake. Maternal 24-h UIE was the best predictor of BMIC.

Higher Levels of Urinary Thiocyanate, a Biomarker of Cruciferous Vegetable Intake, Were Associated With Lower Risks of Cardiovascular Disease and All-Cause Mortality Among Non-smoking Subjects

Background

Epidemiologic studies on cruciferous vegetable (CV) intake and cardiovascular disease (CVD) were inconclusive.

Objective

To investigate the associations of urinary thiocyanate, a biomarker of CV intake, with CVD and all-cause mortality among non-smoking adults.

Methods

This prospective cohort study comprised 10,489 non-smoking adults (weighted mean age, 46.8 years; 43.4% male) from the National Health and Nutrition Examination Survey 2001–2014. Non-smokers were defined as subjects with serum cotinine < 3 ng/mL. Urinary thiocyanate was measured with ion chromatography tandem mass spectrometry at baseline, and CVD and all-cause mortality were identified through linkage to National Death Index until December 31, 2015. Cox proportional hazards model was applied to estimate the hazard ratios (HRs) with 95% confidence intervals (CIs) for CVD and all-cause mortality.

Results

A total of 800 deaths, of which 136 died of CVD, were ascertained within a median 7.8 years of follow-up. Urinary thiocyanate was positively correlated with total CV intake among non-smoking adults (r_s = 0.088, P < 0.001). Comparing extreme quartiles, the multivariate-adjusted HRs for CVD and all-cause mortality were 0.50 (95% CI: 0.29–0.85) and 0.75 (95% CI: 0.60–0.92), respectively. Each 1 μg/g creatinine increment of log-transformed urinary thiocyanate was associated with a 25% (HR: 0.75; 95% CI: 0.62–0.91) reduced CVD mortality risk and 12% (HR: 0.88; 95% CI: 0.81–0.96) reduced all-cause mortality risk. The documented inverse associations persisted in sensitivity analyses.

Conclusion

Increased levels of urinary thiocyanate, a candidate biomarker of CV intake, were associated with low risks of CVD and total mortality among non-smoking adults. This prospective biomarker-based study provided further evidence to support the cardiovascular benefits of CVs.

The Role of Iodine for Thyroid Function in Lactating Women and Infants

Iodine is a micronutrient needed for the production of thyroid hormones, which regulate metabolism, growth, and development. Iodine deficiency or excess may alter the thyroid hormone synthesis. The potential effects on infant development depend on the degree, timing, and duration of exposure. The iodine requirement is particularly high during infancy because of elevated thyroid hormone turnover. Breastfed infants rely on iodine provided by human milk, but the iodine concentration in breast milk is determined by the maternal iodine intake. Diets in many countries cannot provide sufficient iodine, and deficiency is prevented by iodine fortification of salt. However, the coverage of iodized salt varies between countries. Epidemiological data suggest large differences in the iodine intake in lactating women, infants, and toddlers worldwide, ranging from deficient to excessive intake. In this review, we provide an overview of the current knowledge and recent advances in the understanding of iodine nutrition and its association with thyroid function in lactating women, infants, and toddlers. We discuss risk factors for iodine malnutrition and the impact of targeted intervention strategies on these vulnerable population groups. We highlight the importance of appropriate definitions of optimal iodine nutrition and the need for more data assessing the risk of mild iodine deficiency for thyroid disorders during the first 2 years in life.

Breast Milk Iodine Concentration (BMIC) as a Biomarker of Iodine Status in Lactating Women and Children <2 Years of Age: A Systematic Review

Background: Iodine is needed for the production of thyroid hormones, which are essential for infant growth and development. Given that there are wide variations in breast milk iodine concentration (BMIC) and urinary iodine concentration (UIC), it is unclear if BMIC is associated with UIC in populations residing in iodine sufficient or deficient areas. Aim: To investigate if BMIC can be used as a biomarker for iodine status in lactating women and children <2 years of age. Methods: Electronic databases; PubMed, Web of Science and Scopus were searched until year 2021, for studies investigating the relationship between BMIC and UIC. Studies were reviewed for eligibility, according to inclusion and exclusion criteria, followed by data extraction, according to the PRISMA guidelines. Results: Overall, 51 studies met the criteria for inclusion in the systematic review. BMIC ranged from 18 to 1153 µg/L. In iodine-deficient and iodine-sufficient lactating women, BMIC ranged from 26 to 185 µg/L and 15 to 1006 µg/L, respectively. In most studies, the categorisation of iodine status assessed by median UIC was consistent with the categorisation of iodine status assessed by median BMIC cut off of ≥100 µg/L, to determine iodine sufficiency in lactating women and children <2 years of age. Conclusions: The systematic review indicated that BMIC is a promising biomarker of iodine status in lactating women and children <2 years of age. However, these data need to be interpreted cautiously, given the study limitations in the included studies. Future studies should consider investigating the optimal median BMIC, as there is a lack of high-quality observational and intervention studies in lactating women and infants.

Reactive oxygen and nitrogen species and innate immune response

The innate immune system is the first line of defense against pathogens and is characterized by its fast but nonspecific response. One important mechanism of this system is the production of the biocidal reactive oxygen and nitrogen species, which are widely distributed within biological systems, including phagocytes and secretions. Reactive oxygen and nitrogen species are short-lived intermediates that are biochemically synthesized by various enzymatic reactions in aerobic organisms and are regulated by antioxidants. The physiological levels of reactive species play important roles in cellular signaling and proliferation. However, higher concentrations and prolonged exposure can fight infections by damaging important microbial biomolecules. One feature of the reactive species generation system is the interaction between its components to produce more biocidal agents. For example, the phagocytic NADPH oxidase complex generates superoxide, which functions as a precursor for antimicrobial hydrogen peroxide synthesis. Peroxide is then used by myeloperoxidase in the same cells to generate hypochlorous acid, a highly microbicidal agent. Studies on animal models and microorganisms have shown that deficiency of these antimicrobial agents is associated with severe recurrent infections and immunocompromised diseases, such as chronic granulomatous disease. There is accumulating evidence that reactive species have important positive aspects on human health and immunity; however, some important promising features of this system remain obscure.

The Role of Thiocyanate in Modulating Myeloperoxidase Activity during Disease

Thiocyanate (SCN⁻) is a pseudohalide anion omnipresent across mammals and is particularly concentrated in secretions within the oral cavity, digestive tract and airway. Thiocyanate can outcompete chlorine anions and other halides (F⁻, Br⁻, I⁻) as substrates for myeloperoxidase by undergoing two-electron oxidation with hydrogen peroxide. This forms their respective hypohalous acids (HOX where X⁻ = halides) and in the case of thiocyanate, hypothiocyanous acid (HOSCN), which is also a bactericidal oxidative species involved in the regulation of commensal and pathogenic microflora. Disease may dysregulate redox processes and cause imbalances in the oxidative profile, where typically favoured oxidative species, such as hypochlorous acid (HOCl), result in an overabundance of chlorinated protein residues. As such, the pharmacological capacity of thiocyanate has been recently investigated for its ability to modulate myeloperoxidase activity for HOSCN, a less potent species relative to HOCl, although outcomes vary significantly across different disease models. To date, most studies have focused on therapeutic effects in respiratory and cardiovascular animal models. However, we note other conditions such as rheumatic arthritis where SCN⁻ administration may worsen patient outcomes. Here, we discuss the pathophysiological role of SCN⁻ in diseases where MPO is implicated.

Circadian Variation in Human Milk Composition, a Systematic Review

Background: Breastfeeding is considered the most optimal mode of feeding for neonates and mothers. Human milk changes over the course of lactation in order to perfectly suit the infant’s nutritional and immunological needs. Its composition also varies throughout the day. Circadian fluctuations in some bioactive components are suggested to transfer chronobiological information from mother to child to assist the development of the biological clock. This review aims to give a complete overview of studies examining human milk components found to exhibit circadian variation in their concentration. Methods: We included studies assessing the concentration of a specific human milk component more than once in 24 h. Study characteristics, including gestational age, lactational stage, sampling strategy, analytical method, and outcome were extracted. Methodological quality was graded using a modified Newcastle-Ottawa Scale (NOS). Results: A total of 83 reports assessing the circadian variation in the concentration of 71 human milk components were included. Heterogeneity among studies was high. The methodological quality varied widely. Significant circadian variation is found in tryptophan, fats, triacylglycerol, cholesterol, iron, melatonin, cortisol, and cortisone. This may play a role in the child’s growth and development in terms of the biological clock.

Xanthine oxidase-lactoperoxidase system and innate immunity: Biochemical actions and physiological roles

The innate immune system in mammals is the first-line defense that plays an important protective role against a wide spectrum of pathogens, especially during early life before the adaptive immune system develops. The enzymes xanthine oxidase (XO) and lactoperoxidase (LPO) are widely distributed in mammalian tissues and secretions, and have a variety of biological functions including in innate immunity, provoking much interest for both in vitro and in vivo applications. The enzymes are characterized by their generation of reactive oxygen and nitrogen species, including hydrogen peroxide, hypothiocyanite, nitric oxide, and peroxynitrite. XO is a major generator of hydrogen peroxide and superoxide that subsequently trigger a cascade of oxidative radical pathways, including those produced by LPO, which have bactericidal and bacteriostatic effects against pathogens including opportunistic bacteria. In addition to their role in host microbial defense, reactive oxygen and nitrogen species play important physiological roles as second messenger cell signaling molecules, including cellular proliferation, differentiation and gene expression. There are several indications that the reactive species generated by peroxide have positive effects on human health, particularly in neonates; however, some important in vivo aspects of this system remain obscure. The primary dependence of the system on hydrogen peroxide has led us to propose it is particularly relevant to neonate mammals during milk feeding.

Opportunities for evaluating chemical exposures and child health in the United States: the Environmental influences on Child Health Outcomes (ECHO) Program

The Environmental Influences on Child Health Outcomes (ECHO) Program will evaluate environmental factors affecting children's health (perinatal, neurodevelopmental, obesity, respiratory, and positive health outcomes) by pooling cohorts composed of >50,000 children in the largest US study of its kind. Our objective was to identify opportunities for studying chemicals and child health using existing or future ECHO chemical exposure data. We described chemical-related information collected by ECHO cohorts and reviewed ECHO-relevant literature on exposure routes, sources, and environmental and human monitoring. Fifty-six ECHO cohorts have existing or planned chemical biomonitoring data for mothers or children. Environmental phenols/parabens, phthalates, metals/metalloids, and tobacco biomarkers are each being measured by ≥15 cohorts, predominantly during pregnancy and childhood, indicating ample opportunities to study child health outcomes. Cohorts are collecting questionnaire data on multiple exposure sources and conducting environmental monitoring including air, dust, and water sample collection that could be used for exposure assessment studies. To supplement existing chemical data, we recommend biomonitoring of emerging chemicals, nontargeted analysis to identify novel chemicals, and expanded measurement of chemicals in alternative biological matrices and dust samples. ECHO's rich data and samples represent an unprecedented opportunity to accelerate environmental chemical research to improve the health of US children.

Environmental exposure to perchlorate: A review of toxicology and human health

Perchlorate pharmacology and toxicology studies date back at least 65 years in the peer-reviewed literature. Repeated studies in animals and humans have demonstrated perchlorate's mechanism of action, dose-response, and adverse effects over a range of doses. The first measurable effect of perchlorate is inhibition of iodine uptake to the thyroid gland. Adequate levels of thyroid hormones are critical for the development of the fetal nervous system. With sufficient dose and exposure duration, perchlorate can reduce thyroid hormones in the pregnant or non-pregnant woman via this mechanism. The developing fetus is the most sensitive life stage for chemical agents that affect iodide uptake to the thyroid. Perchlorate has a half-life of eight hours, is not metabolized, does not bioaccumulate, is not a mutagen or carcinogen, and is not reprotoxic or immunotoxic. More recently, epidemiological and biomonitoring studies have been published in the peer-reviewed literature characterizing the thyroidal effects of perchlorate and other goitrogens. While the results from most populations report no consistent association, a few studies report thyroidal effects at environmentally relevant levels of perchlorate. We reviewed the literature on health effects of perchlorate at environmental exposure levels, with a focus on exposures during pregnancy and neurodevelopmental effects. Based on the studies we reviewed, health effects are expected to only occur at doses substantially higher than environmental levels.

Environmental Chemicals in Breast Milk and Formula: Exposure and Risk Assessment Implications

BACKGROUND

Human health risk assessment methods have advanced in recent years to more accurately estimate risks associated with exposure during childhood. However, predicting risks related to infant exposures to environmental chemicals in breast milk and formula remains challenging.

OBJECTIVES

Our goal was to compile available information on infant exposures to environmental chemicals in breast milk and formula, describe methods to characterize infant exposure and potential for health risk in the context of a risk assessment, and identify research needed to improve risk analyses based on this type of exposure and health risk information.

METHODS

We reviewed recent literature on levels of environmental chemicals in breast milk and formula, with a focus on data from the United States. We then selected three example publications that quantified infant exposure using breast milk or formula chemical concentrations and estimated breast milk or formula intake. The potential for health risk from these dietary exposures was then characterized by comparison with available health risk benchmarks. We identified areas of this approach in need of improvement to better characterize the potential for infant health risk from this critical exposure pathway.

DISCUSSION

Measurements of chemicals in breast milk and formula are integral to the evaluation of risk from early life dietary exposures to environmental chemicals. Risk assessments may also be informed by research investigating the impact of chemical exposure on developmental processes known to be active, and subject to disruption, during infancy, and by analysis of exposure-response data specific to the infant life stage. Critical data gaps exist in all of these areas.

CONCLUSIONS

Better-designed studies are needed to characterize infant exposures to environmental chemicals in breast milk and infant formula as well as to improve risk assessments of chemicals found in both foods. https://doi.org/10.1289/EHP1953.

Iodine in Human Milk: A Systematic Review

Because infants are born with small amounts of stored intrathyroidal iodine, they depend on human-milk iodine for normal physical and neurologic growth and development. The mammary gland concentrates iodide; however, there is a lack of consensus on the concentrations of breast-milk iodine necessary to achieve equilibrium in the infant. The objectives of the present review are to consider trends in breast-milk iodine concentrations over the course of lactation, to determine which maternal factors or interventions influence breast-milk iodine concentrations, to examine the association between breast-milk iodine concentrations and infant iodine status, and to identify how newer data contribute to the literature and inform recommendations for achieving optimal breast-milk iodine concentrations. A systematic search of the published literature was undertaken by using the US National Library of Medicine's MEDLINE/PubMed bibliographic search engine. Observational and intervention studies were included if the research was original, the study had not been included in a previous review, and iodine concentration in human milk was measured at ≥1 time point during the first 12 mo of lactation. Results of the systematic review indicate that breast-milk iodine concentrations vary widely between populations but are highest in colostrum and decrease gradually throughout the lactation period. Included studies did not replicate earlier findings of an inverse correlation between breast-milk iodine and perchlorate concentrations. Supplementation with high-dose or daily iodine during lactation was effective in increasing breast-milk iodine concentrations with some evidence of a dose-response relationship, which is consistent with findings of earlier supplementation trials in pregnancy and lactation. Although additional and globally representative research is needed, data suggest that breast-milk iodine concentrations in the range of 150 μg/L during the first 6 mo of lactation would achieve or exceed infant iodine equilibrium and prevent the developmental consequences of iodine deficiency.

Micronutrients in Human Milk: Analytical Methods

Exclusive breastfeeding is recommended by the WHO for the first 6 mo of life because human milk protects against gastrointestinal infections and supplies balanced and adequate nutrient contents to the infant. However, reliable data on micronutrient concentrations in human milk are sparse, especially because some micronutrients are affected by maternal diet. Microbiological and competitive protein-binding assays, nuclear magnetic resonance or inductively coupled plasma spectroscopy, and chromatographic analyses are among the methods that have been applied to human-milk micronutrient analysis. However, the validation or evaluation of analytical methods in terms of their suitability for the complex human-milk matrix has been commonly ignored in reports, even though the human-milk matrix differs vastly from blood, plasma, or urine matrixes. Thus, information on the validity, accuracy, and sensitivity of the methods is essential for the estimation of infant and maternal intake requirements to support and maintain adequate milk micronutrient concentrations for healthy infant growth and development. In this review, we summarize current knowledge on methods used for analyzing water- and fat-soluble vitamins as well as iron, copper, zinc, iodine, and selenium in human milk and their different forms in milk; the tools available for quality control and assurance; and guidance for preanalytical considerations. Finally, we recommend preferred methodologic approaches for analysis of specific milk micronutrients.

Breast-Milk Iodine Concentrations and Iodine Levels of Infants According to the Iodine Status of the Country of Residence: A Systematic Review and Meta-Analysis

BACKGROUND

Iodine, an essential micronutrient, plays a critical role in normal growth and development, especially during the first two years of life. This systematic review and meta-analysis is among the first to evaluate breast-milk iodine concentrations and infant iodine status in countries characterized by iodine sufficiency or deficiency.

METHODS

PubMed, Web of Science, Cochrane Library, Google Scholar, and other relevant databases, as well as reference lists of previous reviews, were searched for relevant studies published between 1986 and 2016. Mean or median breast-milk and infant urinary iodine concentrations, along with other relevant data, were extracted from eligible studies. Each study was assessed for quality and risk of bias.

RESULTS

Of the 496 identified studies, 57 met the criteria for inclusion in the meta-analysis. The mean (confidence interval [CI]) iodine concentrations in maternal colostrum were 152.0 μg/L [CI 106.2-198.7 μg/L] and 57.8 μg/L [CI 41.4-74.1 μg/L] in iodine-sufficient and -deficient countries, respectively, indicating a significant difference between the two iodine statuses. By contrast, the corresponding values in mature milk did not differ significantly between mothers in iodine-sufficient and -deficient countries (71.5 μg/L [CI 51.0-92.0 μg/L] and 28.0 μg/L [CI -13.8 to 69.9 μg/L], respectively]. The weighted urinary iodine levels [CIs] of breast-fed infants in iodine-sufficient countries were significantly higher than those in iodine-deficient countries (164.5 μg/L [CI 116.4-212.7 μg/L] vs. 70.4 μg/L [CI 46.2-94.6 μg/L]). Similarly, a significant difference was observed in the pooled estimates of urinary iodine levels [CIs] among formula-fed infants in iodine-sufficient versus iodine-deficient countries (310.3 μg/L [CI 287.4-342.1 μg/L] vs. 38.3 μg/L [CI 23.4-53.2 μg/L]).

CONCLUSION

The meta-analysis reveals that in iodine-sufficient countries, the mean iodine concentrations in colostrum and mature breast milk corresponded to iodine sufficiency among infants. The results are thus compatible with the international recommendation that lactating women and infants younger than two years of age who reside in iodine-sufficient countries do not require iodine supplementation.

Exposure to perchlorate, nitrate and thiocyanate, and prevalence of diabetes mellitus

Background

It is known that perchlorate, nitrate and thiocyanate have the property of inhibiting sodium iodide symporter. Animal studies have suggested that these compounds, especially perchlorate, might also interfere with insulin secretion. However, the association between their exposure and diabetes risk is largely unknown in humans.

Methods

Among 11 443 participants (mean age 42.3 years) from the National Health and Nutritional Examination Survey 2001-14, urinary perchlorate, nitrate and thiocyanate were measured by using ion chromatography coupled with electrospray tandem mass spectrometry. Diabetes was defined as self-reported doctor diagnosis, use of oral hypoglycaemic medication or insulin, fasting plasma glucose ≥ 126 mg/dl or glycated haemoglobin A1c (HbA1c) ≥ 6.5%.

Results

The median (interquartile range) levels of urinary perchlorate, nitrate and thiocyanate were 3.32 (1.84, 5.70) μg/l, 46.4 (27.9, 72.0) mg/l and 1.23 (0.59, 2.78) mg/l, respectively. Higher levels of urinary perchlorate were associated with elevated levels of fasting glucose, HbA1c, insulin and homeostatic model assessment of insulin resistance (all Ptrend < 0.001). After multivariate adjustment including urinary creatinine, smoking status and body mass index (BMI), higher urinary perchlorate, but not nitrate or thiocyanate, was associated with an increased prevalence of diabetes mellitus. Comparing extreme quintiles, the odds ratio (95% confidence interval) of diabetes was 1.53 (1.21, 1.93; Ptrend < 0.001) for perchlorate, 1.01 (0.77, 1.32; Ptrend = 0.44) for nitrate and 0.98 (0.73, 1.31; Ptrend = 0.64) for thiocyanate. When urinary perchlorate, nitrate and thiocyanate were further mutually adjusted, the results did not materially change. Similar results were observed when analyses were stratified by smoking status, as well as by age, gender, kidney function and BMI.

Conclusions

Higher urinary perchlorate levels are associated with an increased prevalence of diabetes mellitus, independent of traditional risk factors. Future prospective studies are needed to confirm these findings.

Stable isotopic composition of perchlorate and nitrate accumulated in plants: Hydroponic experiments and field data

Natural perchlorate (ClO₄^-) in soil and groundwater exhibits a wide range in stable isotopic compositions (δ³⁷Cl, δ¹⁸O, and Δ¹⁷O), indicating that ClO₄^- may be formed through more than one pathway and/or undergoes post-depositional isotopic alteration. Plants are known to accumulate ClO₄^-, but little is known about their ability to alter its isotopic composition. We examined the potential for plants to alter the isotopic composition of ClO₄^- in hydroponic and field experiments conducted with snap beans (Phaseolus vulgaris L.). In hydroponic studies, anion ratios indicated that ClO₄^- was transported from solutions into plants similarly to NO₃^- but preferentially to Cl^- (4-fold). The ClO₄^- isotopic compositions of initial ClO₄^- reagents, final growth solutions, and aqueous extracts from plant tissues were essentially indistinguishable, indicating no significant isotope effects during ClO₄^- uptake or accumulation. The ClO₄^- isotopic composition of field-grown snap beans was also consistent with that of ClO₄^- in varying proportions from irrigation water and precipitation. NO₃^- uptake had little or no effect on NO₃^- isotopic compositions in hydroponic solutions. However, a large fractionation effect with an apparent ε (¹⁵N/¹⁸O) ratio of 1.05 was observed between NO₃^- in hydroponic solutions and leaf extracts, consistent with partial NO₃^- reduction during assimilation within plant tissue. We also explored the feasibility of evaluating sources of ClO₄^- in commercial produce, as illustrated by spinach, for which the ClO₄^- isotopic composition was similar to that of indigenous natural ClO₄^-. Our results indicate that some types of plants can accumulate and (presumably) release ClO₄^- to soil and groundwater without altering its isotopic characteristics. Concentrations and isotopic compositions of ClO₄^- and NO₃^- in plants may be useful for determining sources of fertilizers and sources of ClO₄^- in their growth environments and consequently in food supplies.

Investigation of concentration of thiocyanate ion in raw cow's milk from China, New Zealand and the Netherlands

Thiocyanate ion is a natural component of cow's milk (hereinafter as milk) which may be artificially augmented to activate the lactoperoxidase milk preservation system. This study presents a survey of thiocyanate levels in raw milk and proposes a naturally occurring baseline concentration of thiocyanate in milk, which is the basis for market supervision. 1669 raw milk samples from China, 270 samples from New Zealand and 120 from the Netherlands were collected in the survey. 65% of the samples contained thiocyanate above the detection limit. The average concentration of thiocyanate was 2.11mg/kg (0.10-16.20mg/kg). Differences in the concentrations of thiocyanate were found among three countries, the 12 selected provinces in China, and between summer and winter. The baseline concentration of thiocyanate found in raw cow's milk was statistically calculated and rounded to 9.0mg/kg. Thiocyanate in milk at this level does not present a food safety concern.

Assessing the potential impact on the thyroid axis of environmentally relevant food constituents/contaminants in humans

Occurrence and mode of action of potentially relevant goitrogens in human nutrition and their mode of action (MOA) are reviewed, with special focus on the anionic iodine uptake inhibitors perchlorate (PER), thiocyanate (SCN) and nitrate (NO3). Epidemiological studies suggest persistent halogenated organic contaminants and phthalates as well as certain antimicrobials to deserve increased attention. This also applies to natural goitrogens, including polyphenols and glucosinolates, food constituents with limited data density concerning human exposure. Glucosinolates present in animal feed are presumed to contribute to SCN transfer into milk and milk products. PER, SCN and NO3 are well-investigated environmental goitrogens in terms of MOA and relative potency. There is compelling evidence from biomarker monitoring that the exposure to the goitrogens SCN and NO3 via human nutrition exceeds that of PER by orders of magnitude. The day-to-day variation in dietary intake of these substances (and of iodide) is concluded to entail corresponding variations in thyroidal iodide uptake, not considered as adverse to health or toxicologically relevant. Such normal variability of nutritional goitrogen uptake provides an obvious explanation for the variability in radioactive iodine uptake (RAIU) measurements observed in healthy individuals. Based on available data, a 20 % change in the thyroidal uptake of iodide is derived as threshold value for a biologically meaningful change induced by perchlorate and other goitrogens with the same MOA. We propose this value to be used as the critical effect size or benchmark response in benchmark dose analysis of human RAIU data. The resulting BMDL20 is 0.0165 mg/kg bw/day or 16.5 μg/kg bw/day. Applying a factor of 4, to allow for inter-human differences in toxicokinetics, leads to a TDI for perchlorate of 4 μg/kg bw/day.

Iodine Concentration in Breastmilk and Urine among Lactating Women of Bhaktapur, Nepal

Adequate iodine concentration in breastmilk (BMIC) is essential for optimal neonatal thyroid hormone synthesis and neurological development in breastfed infants. For many decades, iodine deficiency has been a public health problem in Nepal. However, recently, excessive iodine intakes among Nepali infants have been reported. This study aimed to measure BMIC and urinary iodine concentration (UIC) among lactating women in a peri-urban area of Nepal. Iodine concentration was measured in spot urine (n = 485) and breastmilk samples (n = 291) of 500 randomly selected lactating women. The median (p25, p75) BMIC and median UIC were 250 (130, 370) µg/L and 230 (135-377) µg/L, respectively. Around 82% had BMIC > 100 µg/L, 61% had BMIC > 200 µg/L and 81% had UIC > 100 µg/L, 37% had >300 µg/L and 20% had >500 µg/L. In multiple linear regression models, time since birth (β 3.0, 95% CI (0.2, 5.0)) and UIC (β 1.0, 95% CI (0.1, 2.0)) were associated with BMIC, explaining 26% of the variance. A large proportion of the women had adequate BMIC and UIC; however, a subset had high iodine concentrations. These findings emphasize the importance of carefully monitoring iodine intake to minimize the risk of iodine excess and subsequently preventing transient iodine-induced hypothyroidism in breastfed infants.

Placental transfer of and infantile exposure to perchlorate

Fetuses and infants are vulnerable to perchlorate toxicity. We assessed fetal and infantile exposure to perchlorate in two Chinese cities (Nanchang and Tianjin). Perchlorate was widely found (82%-100%) in breast milk, dissolved infant formula, infants' urine, maternal and cord blood samples. Perchlorate levels in infants' urine (mean ± standard deviation: 22.4 ± 35.6 ng mL(-1)), breast milk (36.6 ± 48.1 ng mL(-1)), and cord blood (3.18 ± 3.83 ng mL(-1)) samples collected from Nanchang and Tianjin were approximately an order of magnitude higher than those reported for the U.S. Perchlorate concentrations in cord blood were comparable to that in maternal blood, indicating that perchlorate is transferred from mother to fetus through placenta. Among all infants providing urine samples, the average daily intake of perchlorate (DOSEU) was estimated to be 1.17 ± 1.57 μg kg(-1) bw d(-1), and 40% of these infants had DOSEU exceeding the RfD (0.7 μg kg(-1) bw d(-1)) recommended by U.S. EPA. However, approximately 70% of exclusively breast-fed infants had perchlorate exposure dose via breast milk exceeding the RfD. For breast-fed infants, breast milk was the overwhelmingly predominant exposure pathway; while infant formula and indoor dust ingestion were major perchlorate exposure sources for formula-fed infants. To our knowledge, this is the first report to assess the fetal and infantile exposure to perchlorate in China.

Perchlorate in indoor dust and human urine in China: contribution of indoor dust to total daily intake

Perchlorate is used in fireworks and China is the largest fireworks producer and consumer in the world. Information regarding human exposure to perchlorate is scarce in China, and exposure via indoor dust ingestion (EDI indoor dust) has rarely been evaluated. In this study, perchlorate was found in indoor dust (detection rate: 100%, median: 47.4 μg/g), human urine (99%, 26.2 ng/mL), drinking water (100%, 3.99 ng/mL), and dairy milk (100%, 12.3 ng/mL) collected from cities that have fireworks manufacturing areas (Yueyang and Nanchang) and in cities that do not have fireworks manufacturing industries (Tianjin, Shijiazhuang, Yuxi and Guilin) in China. In comparison with perchlorate levels reported for other countries, perchlorate levels in urine samples from fireworks sites and nonfireworks sites in China were higher. Median indoor dust perchlorate concentrations were positively correlated (r = 0.964, p < 0.001) with outdoor dust perchlorate levels reported previously. The total daily intake (EDI total) of perchlorate, estimated based on urinary levels, ranged from 0.090 to 27.72 μg/kg body weight (bw)/day for all studied participants; the percentage of donors who had EDI total exceeding the reference dose (RfD) recommended by the United States Environmental Protection Agency (US EPA) was 79%, 48%, and 25% for toddlers (median: 1.829 μg/kg bw/day), adults (0.669 μg/kg bw/day), and children (median: 0.373 μg/kg bw/day), respectively. Toddlers (0.258 μg/kg bw/day) had the highest median EDI indoor dust, which was 2 to 5 times greater than the EDI indoor dust calculated for other age groups (the range of median values: 0.044 to 0.127 μg/kg bw/day). Contribution of indoor dust to EDItotal was 26%, 28%, and 7% for toddlers, children, and adults, respectively. Indoor dust contributed higher percentage to EDI total than that by dairy milk (0.5-5%).

Hofmeister effect of salt mixtures on thermo-responsive poly(propylene oxide)

The Hofmeister effect of salt mixtures is strongly dependent on composition of the mixture as well as absolute and relative concentration of the salts.

Occurrence of perchlorate and thiocyanate in human serum from e-waste recycling and reference sites in Vietnam: association with thyroid hormone and iodide levels

Perchlorate (ClO4 (-)) and thiocyanate (SCN(-)) interfere with iodide (I(-)) uptake by the sodium/iodide symporter, and thereby these anions may affect the production of thyroid hormones (THs) in the thyroid gland. Although human exposure to perchlorate and thiocyanate has been studied in the United States and Europe, few investigations have been performed in Asian countries. In this study, we determined concentrations of perchlorate, thiocyanate, and iodide in 131 serum samples collected from 2 locations in Northern Vietnam, Bui Dau (BD; electrical and electronic waste [e-waste] recycling site) and Doung Quang (DQ; rural site) and examined the association between serum levels of these anions with levels of THs. The median concentrations of perchlorate, thiocyanate, and iodide detected in the serum of Vietnamese subjects were 0.104, 2020, and 3.11 ng mL(-1), respectively. Perchlorate levels were significantly greater in serum of the BD population (median 0.116 ng mL(-1)) than those in the DQ population (median 0.086 ng mL(-1)), which indicated greater exposure from e-waste recycling operations by the former. Serum concentrations of thiocyanate were not significantly different between the BD and DQ populations, but increased levels of this anion were observed among smokers. Iodide was a significant positive predictor of serum levels of FT3 and TT3 and a significant negative predictor of thyroid-stimulating hormone in males. When the association between serum levels of perchlorate or thiocyanate and THs was assessed using a stepwise multiple linear regression model, no significant correlations were found. In addition to greater concentrations of perchlorate detected in the e-waste recycling population, however, given that lower concentrations of iodide were observed in the serum of Vietnamese females, detailed risk assessments on TH homeostasis for females inhabiting e-waste recycling sites, especially for pregnant women and their neonates, are required.

Excess iodinuria in infants and its relation to the iodine in maternal milk

OBJECTIVE

Iodine is an essential micro nutrient, and a deficiency or excessive intake of this mineral is related to changes in thyroid function. In Brazil, both deficiency and excessive intake of iodine are common; however, excessive intakes have recently been observed. Thus, the objective of the present study was to assess the iodine concentration in maternal milk, taking into account the salt iodine concentration of the participating households and in the infants' urine.

METHOD

Urine samples from 33 infants (less than 6 months of age), maternal milk samples and samples of the kitchen salt used by the mothers were collected. The iodine levels in the urine and maternal milk were assessed by ICP-MS; the iodine levels in the salt were assessed by titration.

RESULT

The median iodinuria value in the infants was 293 μg/L; the mean iodine concentration was 206 μg/L in the maternal milk and 39.9 mg I/kg in the salt. There was a positive correlation between the iodine concentration in the maternal milk and the infant iodinuria value.

CONCLUSION

The median infant iodinuria was elevated due to the high iodine concentration present in the maternal milk. High iodine values were caused by high salt iodine levels, which should be reduced.

Breastmilk iodine concentrations following acute dietary iodine intake

BACKGROUND

Breastmilk iodine levels may vary temporally in response to recent changes in dietary iodine intake. We assessed the effect of and time to peak breastmilk iodine levels after potassium iodine ingestion, which has never been studied and is important toward interpretation of studies of breastmilk iodine measurements.

METHODS

Sixteen healthy lactating Boston-area women with no known thyroid disease were each given 600 μg oral potassium iodide (KI) (456 μg iodine) after an overnight fast. Iodine was measured in breastmilk and urine at baseline and hourly for 8 hours following iodine intake. All dietary iodine ingested during the study period was also measured.

RESULTS

Mean age of mothers was 30.2±4.1 (SD) years. Median (interquartile range [IQR]) baseline breastmilk and urine iodine levels were 45.5 μg/L (IQR 34.5-169.0) and 67.5 μg/L (IQR 57.5-140.0), respectively. Following 600 μg KI administration, median increase in breastmilk iodine levels above baseline was 280.5 μg/L (IQR 71.5-338.0), and median peak breastmilk iodine concentration was 354 μg/L (IQR 315-495). Median time to peak breastmilk iodine levels following KI administration was 6 hours (IQR 5-7). Dietary iodine sources provided an additional 36-685 μg iodine intake during the 8-hour study.

CONCLUSIONS

Following ingestion of 600 μg KI, there is a measurable rise in breastmilk iodine concentrations, with peak levels occurring at 6 hours. These findings strongly suggest that breastmilk iodine concentrations should be interpreted in relation to recent iodine intake.

Environmental perchlorate and thiocyanate exposures and infant serum thyroid function

BACKGROUND

Breastfed infants rely on maternal iodine for thyroid hormone production required for neurodevelopment. Dietary iodine among women of childbearing age in the United States may be insufficient. Perchlorate (competitive inhibitor of the sodium/iodide symporter [NIS]) exposure is ubiquitous. Thiocyanate, from cigarettes and diet, is a weaker NIS inhibitor. Environmental perchlorate and thiocyanate exposures could decrease breast milk iodine by competitively inhibiting NIS in lactating breasts (thus impairing infants' iodine availability), and/or infants' thyroidal NIS to directly decrease infant thyroid function. The current study assessed the relationships between environmental perchlorate and thiocyanate exposures and infant serum thyroid function.

METHODS

Iodine, perchlorate, and thiocyanate in breast milk, maternal and infant urine, and infant serum thyroid function tests were cross-sectionally measured in Boston-area women and their 1-3 month-old breastfed infants. Univariate and multivariable analyses assessed relationships between iodine, perchlorate, thiocyanate, thyroid-stimulating hormone (TSH), and free thyroxine (FT4) levels.

RESULTS

In 64 mothers and infants, median (range) iodine levels were 45.6 μg/L (4.3-1080) in breast milk, 101.9 μg/L (27-570) in maternal urine, and 197.5 μg/L (40-785) in infant urine. Median perchlorate concentrations were 4.4 μg/L (0.5-29.5) in breast milk, 3.1 μg/L (0.2-22.4) in maternal urine, and 4.7 μg/L (0.3-25.3) in infant urine. There were no correlations between infant TSH or FT4 and iodine, perchlorate, and thiocyanate levels in breast milk, maternal urine, and infant urine. In multivariable analyses, perchlorate and thiocyanate levels in breast milk, maternal urine, and infant urine were not significant predictors of infant TSH or FT4.

CONCLUSIONS

Boston-area mothers and their breastfed infants are generally iodine sufficient. Although environmental perchlorate and thiocyanate are ubiquitous, these results do not support the concern that maternal and infant environmental perchlorate and thiocyanate exposures affect infant thyroid function.

Thiocyanate: a potentially useful therapeutic agent with host defense and antioxidant properties

Thiocyanate (SCN) functions in host defense as part of the secreted lactoperoxidase (LPO) microbicidal pathway. SCN is the preferred substrate for LPO-driven catalytic reduction of hydrogen peroxide (H(2)O(2)) forming hypothiocyanous acid (HOSCN). HOSCN is selectively generated by many peroxidase enzymes that can utilize SCN including: eosinophil peroxidase (EPO), gastric peroxidase (GPO), myeloperoxidase (MPO), salivary peroxidase (SPO), and thyroid peroxidase (TPO). These enzymes generate HOSCN through a two-electron halogenation reaction. HOSCN is a potent microbicidal agent that kills or nullifies invading pathogens but is better tolerated by host tissue. Some controversy exists as to whether physiologic levels of HOSCN are non-toxic to host tissue, but the disagreement appears to be based on results of enzymatic generation (yielding moderate steady-state exposure) versus direct high level acute exposure in mammalian cell lines. This apparent duality is also true of other endogenous oxidants such as hydrogen peroxide and relates to the difference between physiologically relevant oxidant production versus supra-physiologic bolus dosing approaches. SCN has antioxidant properties that include the ability to protect cells against oxidizing agents such as hypochlorous acid (HOCl) and repair protein chloramines. SCN is an important endogenous molecule that has the potential to interact in complex and elegant ways with its host environment and foreign organisms. SCN's diverse properties as both host defense and antioxidant agent make it a potentially useful therapeutic.

Hormones and endocrine-disrupting chemicals: low-dose effects and nonmonotonic dose responses

For decades, studies of endocrine-disrupting chemicals (EDCs) have challenged traditional concepts in toxicology, in particular the dogma of "the dose makes the poison," because EDCs can have effects at low doses that are not predicted by effects at higher doses. Here, we review two major concepts in EDC studies: low dose and nonmonotonicity. Low-dose effects were defined by the National Toxicology Program as those that occur in the range of human exposures or effects observed at doses below those used for traditional toxicological studies. We review the mechanistic data for low-dose effects and use a weight-of-evidence approach to analyze five examples from the EDC literature. Additionally, we explore nonmonotonic dose-response curves, defined as a nonlinear relationship between dose and effect where the slope of the curve changes sign somewhere within the range of doses examined. We provide a detailed discussion of the mechanisms responsible for generating these phenomena, plus hundreds of examples from the cell culture, animal, and epidemiology literature. We illustrate that nonmonotonic responses and low-dose effects are remarkably common in studies of natural hormones and EDCs. Whether low doses of EDCs influence certain human disorders is no longer conjecture, because epidemiological studies show that environmental exposures to EDCs are associated with human diseases and disabilities. We conclude that when nonmonotonic dose-response curves occur, the effects of low doses cannot be predicted by the effects observed at high doses. Thus, fundamental changes in chemical testing and safety determination are needed to protect human health.

Summary of an NIH workshop to identify research needs to improve the monitoring of iodine status in the United States and to inform the DRI

The Office of Dietary Supplements (ODS) at the NIH sponsored a workshop on May 12-13, 2011, to bring together representatives from various NIH institutes and centers as a first step in developing an NIH iodine research initiative. The workshop also provided an opportunity to identify research needs that would inform the dietary reference intakes for iodine, which were last revised in 2001. Iodine is required throughout the life cycle, but pregnant women and infants are the populations most at risk of deficiency, because iodine is required for normal brain development and growth. The CDC monitors iodine status of the population on a regular basis, but the status of the most vulnerable populations remains uncertain. The NIH funds very little investigator-initiated research relevant to iodine and human nutrition, but the ODS has worked for several years with a number of other U.S. government agencies to develop many of the resources needed to conduct iodine research of high quality (e.g., validated analytical methods and reference materials for multiple types of samples). Iodine experts, scientists from several U.S. government agencies, and NIH representatives met for 2 d to identify iodine research needs appropriate to the NIH mission.

Breastfed infants metabolize perchlorate

Bifidobacteria are the dominant intestinal bacteria in breastfed infants. It is known that they can reduce nitrate. Although no direct experiments have been conducted until now, inferred pathways for Bifidobacterium bifidum include perchlorate reduction via perchlorate reductase. We show that when commercially available strains of bifidobacteria are cultured in milk, spiked with perchlorate, perchlorate is consumed. We studied 13 breastfed infant-mother pairs who provided 43 milk samples and 39 infant urine samples, and 5 formula-fed infant-mother pairs who provided 21 formula samples and 21 infant urine samples. Using iodine as a conservative tracer, we determined the average urinary iodine (UI) to milk iodine (MI) concentration ratio to be 2.87 for the breastfed infants. For the same samples, the corresponding perchlorate concentration ratio was 1.37 (difference significant, p < 0.001), indicating that perchlorate is lost. For the formula fed infant group the same ratios were 1.20 and 1.58; the difference was not significant (p = 0.68). However, the small number of subjects in the latter group makes it more difficult to conclude definitively whether perchlorate reduction does or does not occur.

Perchlorate, iodine supplements, iodized salt and breast milk iodine content

This study was undertaken to determine if increasing maternal iodine intake through single dose tablets will decrease breast milk concentrations of the iodine-uptake inhibitor, perchlorate, through competitive inhibition. We also sought to determine if the timing of supplementation influences the fraction of iodine excreted in milk versus urine and to compare the effectiveness of iodized salt as a means of providing iodine to breastfed infants. Thirteen women who did not use supplements, seven of whom used iodized salt and six of whom used non-iodized salt, submitted four milk samples and a 24-h urine collection daily for three days. Women repeated the sampling protocol for three more days during which ~150μg of iodine were taken in the evening and again for three days with morning supplementation. Samples were analyzed using isotope-dilution inductively-coupled plasma-mass spectrometry for iodine and isotope-dilution ion chromatography-tandem mass spectrometry for perchlorate. No statistically significant differences were observed in milk iodine or perchlorate concentrations during the two treatment periods. Estimated perchlorate intake was above the U.S. National Academy of Sciences suggested reference dose for most infants. Single daily dose iodine supplementation was not effective in decreasing milk perchlorate concentrations. Users of iodized salt had significantly higher iodine levels in milk than non-users. Iodized salt may be a more effective means of iodine supplementation than tablets.

Temporal variability in urinary concentrations of perchlorate, nitrate, thiocyanate and iodide among children

Perchlorate, nitrate and thiocyanate are ubiquitous in the environment, and human exposure to these chemicals is accurately measured in urine. Biomarkers of these chemicals represent a person's recent exposure, however, little is known on the temporal variability of the use of a single measurement of these biomarkers. Healthy Hispanic and Black children (6-10-year-old) donated urine samples over 6 months. To assess temporal variability, we used three statistical methods (n=29; 153 urine samples): intraclass correlation coefficient (ICC), Spearman's correlation coefficient between concentrations measured at different timepoints and surrogate category analysis to assess how well tertile ranking by a single biomarker measurement represented the average concentration over 6 months. The ICC measure of reproducibility was poor (0.10-0.12) for perchlorate, nitrate and iodide; and fair for thiocyanate (0.36). The correlations for each biomarker across multiple sampling times ranged from 0.01-0.57. Surrogate analysis showed consistent results for almost every surrogate tertile. Results demonstrate fair temporal reliability in the spot urine concentrations of the three NIS inhibitors and iodide. Surrogate analysis show that single-spot urine samples reliably categorize participant's exposure providing support for the use of a single sample as an exposure measure in epidemiological studies that use relative ranking of exposure.

Iodine nutrition in pregnancy and lactation

Adequate iodine intake is required for the synthesis of thyroid hormones that are important for normal fetal and infant neurodevelopment. In this review, we discuss iodine physiology during pregnancy and lactation, methods to assess iodine sufficiency, the importance of adequate iodine nutrition, studies of iodine supplementation during pregnancy and lactation, the consequences of hypothyroidism during pregnancy, the current status of iodine nutrition in the United States, the global efforts toward achieving universal iodine sufficiency, and substances that may interfere with iodine use.

Determination of perchlorate in infant formula by isotope dilution ion chromatography/tandem mass spectrometry

A sensitive and selective isotope dilution ion chromatography/tandem mass spectrometry (ID IC-MS/MS) method was developed and validated for the determination of perchlorate in infant formula. The perchlorate was extracted from infant formula by using 20 ml of methanol and 5 ml of 1% acetic acid. All samples were spiked with (18)O(4) isotope-labelled perchlorate internal standard prior to extraction. After purification on a graphitised carbon solid-phase extraction column, the extracts were injected into an ion chromatography system equipped with an Ionpac AS20 column for separation of perchlorate from other anions. The presence of perchlorate in samples was quantified by isotope dilution mass spectrometry. Analysis of both perchlorate and its isotope-labelled internal standard was carried out on a Waters Quattro Ultima triple quadrupole mass spectrometer operating in a multiple reaction monitoring (MRM) negative ionisation mode. The method was validated for linearity and range, accuracy, precision, sensitivity, and matrix effects. The limit of quantification (LOQ) was 0.4 µg l(-1) for liquid infant formula and 0.95 µg kg(-1) for powdered infant formula. The recovery ranged from 94% to 110% with an average of 98%. This method was used to analyse 39 infant formula, and perchlorate concentrations ranging from <LOQ to 13.5 µg l(-1).

Pendrin mediates uptake of perchlorate in a mammalian in vitro system

Perchlorate is a known endocrine disruptor present in groundwater, vegetables and dairy food products in many regions of the United States. It interferes with the uptake of iodide into the thyrocyte by the sodium-iodide symporter at the basolateral surface, thus potentially disrupting the synthesis of thyroid hormone. Because transport of iodide from the thyroid follicular cells to the follicular lumen is mediated by the protein pendrin at the apical surface, we hypothesized that perchlorate may also interact with this protein. Therefore, HeLa cells were transfected with the human SLC26A4 gene, which encodes pendrin, to generate an in vitro mammalian system expressing the recombinant pendrin protein (HeLa-PDS). The HeLa-PDS cells, along with untransfected cells, were then cultured in presence of iodide and/or perchlorate. Intracellular levels of these two chemicals were measured by ion chromatography tandem mass spectrometry. Results from this study show that iodide and perchlorate uptake increases significantly in HeLa-PDS cells as compared to untransfected cells. Thus, recombinant HeLa cells expressing pendrin protein accumulate iodide and perchlorate intracellularly, indicating that pendrin is involved in the uptake of perchlorate. Additional results from this study suggest that iodide and perchlorate competitively inhibit each other for uptake by pendrin. The ability of perchlorate to compete with iodide for uptake by both basal and apical transporters may increase the potential of perturbation of thyroid homeostasis and therefore the estimated risk posed to susceptible human populations.

Perchlorate in soybean sprouts (Glycine max L. Merr.), water dropwort (Oenanthe stolonifera DC.), and lotus (Nelumbo nucifera Gaertn.) root in South Korea

The occurrence of perchlorate in soybean sprouts (Glycine max L. Merr), water dropwort (Oenanthe stolonifera DC.), and lotus (Nelumbo nucifera Gaertn.) root, which are commonly consumed by people in South Korea, was determined by using an ion chromatograph coupled with a tandem mass spectrometer. For soybean sprouts (11 samples), perchlorate was detected in most (91%) of the samples at various concentrations of up to 78.4 μg/kg dry weight (DW); the mean concentration was 35.2 μg/kg DW. For water dropwort, of the 13 samples examined, four showed concentrations that were above the limit of quantification (LOQ). The mean perchlorate concentration was 20.7 μg/kg DW, and the highest perchlorate value was 39.9 μg/kg DW. Of the six lotus root samples examined, only one exhibited a detectable perchlorate concentration (17.3 μg/kg DW). For the accumulation experiments with artificially contaminated solutions, the concentrations of perchlorate in soybean sprouts gradually increased with the increase of perchlorate concentration in the solution. However, there was a decrease in the bioconcentration factor as the perchlorate concentration in the solution increased.

Estimating perchlorate exposure from food and tap water based on US biomonitoring and occurrence data

Human biomonitoring data show that exposure to perchlorate is widespread in the United States. The predominant source of intake is food, whereas drinking water is a less frequent and far smaller contributor. We used spot urine samples for over 2700 subjects and estimated 24 h intake using new creatinine adjustment equations. Merging data from surveys of national health (NHANES) with drinking water monitoring (UCMR), we categorized survey participants according to their potential exposure through drinking water or food. By subtracting daily food doses of perchlorate from the oral reference dose (RfD), we derive an allowances for perchlorate in tap water for several populations. The calculated mean food perchlorate dose in the United States was 0.081 μg/kg/day compared to 0.101 μg/kg/day for those who also had a potential drinking water component. The calculated 95th percentile doses, typically falling between 0.2 and 0.4 μg/kg/day, were well below the RfD (0.7 μg/kg/day) in all populations analyzed. Children aged 6-11 years had the highest mean perchlorate doses in food (0.147 μg/kg/day), with an additional water contribution of only 0.003 μg/kg/day representing just 2% of exposure. Pregnant women had a mean food dose of 0.093 vs 0.071 μg/kg/day for all women of reproductive age. At the 95th percentile intake for both the total population and women of child-bearing age (15-44), the perchlorate contribution from food was 86% and from drinking water 14% (respectively, 30% and 5% of the RfD). At the mean for the same groups, the food to water contribution ratio is approximately 80:20. We calculate that an average 66 kg pregnant woman consuming a 90th percentile food dose (0.198 μg/kg/day) could also drink the 90th percentile of community water for pregnant women (0.033 l/kg/day) containing 15 μg/l perchlorate without exceeding the 0.7 μg/kg/day reference dose.

Perchlorate exposure and dose estimates in infants

Perchlorate is a naturally occurring inorganic anion used as a component of solid rocket fuel, explosives, and pyrotechnics. Sufficiently high perchlorate intakes can modify thyroid function by competitively inhibiting iodide uptake in adults; however, little is known about perchlorate exposure and health effects in infants. Food intake models predict that infants have higher perchlorate exposure doses than adults. For this reason, we measured perchlorate and related anions (nitrate, thiocyanate, and iodide) in 206 urine samples from 92 infants ages 1-377 days and calculated perchlorate intake dose for this sample of infants. The median estimated exposure dose for this sample of infants was 0.160 μg/kg/day. Of the 205 individual dose estimates, 9% exceeded the reference dose of 0.7 μg/kg/day; 6% of infants providing multiple samples had multiple perchlorate dose estimates above the reference dose. Estimated exposure dose differed by feeding method: breast-fed infants had a higher perchlorate exposure dose (geometric mean 0.220 μg/kg/day) than infants consuming cow milk-based formula (geometric mean 0.103 μg/kg/day, p < 0.0001) or soy-based formula (geometric mean 0.027 μg/kg/day, p < 0.0001), consistent with dose estimates based on dietary intake data. The ability of perchlorate to block adequate iodide uptake by the thyroid may have been reduced by the iodine-sufficient status of the infants studied (median urinary iodide 125 μg/L). Further research is needed to see whether these perchlorate intake doses lead to any health effects.