Iodine Nutrition in Weaning Infants in the United States.

BACKGROUND: As iodine is a requisite micronutrient for infant brain development, infants are at risk for iodine deficiency during the weaning period when their diet transitions from milk (breast-milk, infant formula, or follow-on formula) to solid food. Dietary iodine intake during this weaning period is likely minimal, as the iodine content of commercial baby food is not regulated, and the addition of salt to baby food is not recommended. This study reports the current status of iodine nutrition among weaning infants in the United States. METHODS: Subjects (n = 60; 50% Caucasian, 30% black) were infants <12 months of age who were fed any combination of formula and/or baby food. Samples of all formula and food consumed in the previous 24 hours and a spot urine sample from each infant were obtained for the measurement of iodine. The estimated quantities of ingested formula and baby food were summed from a food diary recorded by the infants' parents. RESULTS: The mean age of the infants was 6.3 ± 3.5 months. The median urinary iodine concentration (UIC) was 117 µg/L (range 26.9-1302.8 µg/L). Estimated daily iodine intake obtained from the measured iodine content in infant formula/foods was 89 µg (range 0-288 µg). There was a positive correlation between the infants' UIC and the iodine content in the consumed foods (r = 0.4, p < 0.001). CONCLUSIONS: Although the median UIC of infants fed a combination of infant formula and baby food would meet the criteria for iodine sufficiency in a larger sample, those consuming the lowest quartile of iodine-containing nutritional sources had a median UIC <100 µg/L.

Urinary Iodine, Perchlorate, and Thiocyanate Concentrations in U.S. Lactating Women.

BACKGROUND: Iodine is an essential micronutrient for thyroid hormone production. Adequate iodine intake and normal thyroid function are important during early development, and breastfed infants rely on maternal iodine excreted in breast milk for their iodine nutrition. The proportion of women in the United States of childbearing age with urinary iodine concentration (UIC) <50 µg/L has been increasing, and a subset of lactating women may have inadequate iodine intake. UIC may also be influenced by environmental exposure to perchlorate and thiocyanate, competitive inhibitors of iodine transport into thyroid, and lactating mammary glands. Data regarding UIC in U.S. lactating women are limited. To adequately assess the iodine sufficiency of lactating women and potential associations with environmental perchlorate and thiocyanate exposure, we conducted a multicenter, cross-sectional study of urinary iodine, perchlorate, and thiocyanate concentrations in healthy U.S. lactating women. METHODS: Lactating women ≥18 years of age were recruited from three U.S. geographic regions: California, Massachusetts, and Ohio/Illinois from November 2008 to June 2016. Demographic information and multivitamin supplements use were obtained. Iodine, perchlorate, and thiocyanate levels were measured from spot urine samples. Correlations between urinary iodine, perchlorate, and thiocyanate levels were determined using Spearman's rank correlation. Multivariable regression models were used to assess predictors of urinary iodine, perchlorate, and thiocyanate levels, and UIC <100 µg/L. RESULTS: A total of 376 subjects (≥125 from each geographic region) were included in the final analyses [mean (SD) age 31.1 (5.6) years, 37% white, 31% black, and 11% Hispanic]. Seventy-seven percent used multivitamin supplements, 5% reported active cigarette smoking, and 45% were exclusively breastfeeding. Median urinary iodine, perchlorate, and thiocyanate concentrations were 143 µg/L, 3.1 µg/L, and 514 µg/L, respectively. One-third of women had UIC <100 µg/L. Spot urinary iodine, perchlorate, and thiocyanate levels all significantly positively correlated to each other. No significant predictors of UIC, UIC <100 µg/L, or urinary perchlorate levels were identified. Smoking, race/ethnicity, and marital status were significant predictors of urinary thiocyanate levels. CONCLUSION: Lactating women in three U.S. geographic regions are iodine sufficient with an overall median UIC of 143 µg/L. Given ubiquitous exposure to perchlorate and thiocyanate, adequate iodine nutrition should be emphasized, along with consideration to decrease these exposures in lactating women to protect developing infants.

Iodine Supplementation in Women During Preconception, Pregnancy, and Lactation: Current Clinical Practice by U.S. Obstetricians and Midwives.

BACKGROUND: Iodine deficiency is a major public-health problem throughout the world, especially for pregnant women, and it is considered the most common cause of preventable intellectual impairment. In the United States, iodine status in pregnant women is considered mildly deficient. Therefore, the Endocrine Society, the American Thyroid Association, the Teratology Society, and the American Academy of Pediatrics recommend that women receive prenatal vitamins containing 150 µg of iodine daily during preconception, pregnancy, and lactation. The objectives of this study were to evaluate awareness of iodine nutrition among obstetricians and midwives in the United States, and to document current clinical practice regarding recommendations for iodine supplementation for women during preconception, pregnancy, and lactation. METHODS: All midwife members of the American College of Nurse-Midwives (ACNM) and all obstetrician members of the American Medical Association (AMA) were invited to participate in a web-based survey. RESULTS: A total of 199 midwives and 277 obstetricians participated in the survey. One third of both obstetricians and midwives considered iodine status in U.S. pregnant women to be deficient. Although almost all obstetricians and midwives would recommend prenatal multivitamins, most reported rarely or never recommending iodine-containing multivitamins for women planning pregnancy (68.7% and 70.2%, respectively), pregnant women (66% and 67.1%), or lactating women (68.7% and 71.7%). Of the respondents who did report prescribing iodine-containing supplements, 85% recommended supplementation during the first trimester and 75-80% during the second and third trimesters. However, of those who did recommend iodine supplementation, only 45% would prescribe the recommended 150 µg of iodine daily during pregnancy. Overall, 75% of U.S. obstetricians and midwives do not recommend or would recommend an inadequate amount of iodine during preconception, pregnancy, and lactation. CONCLUSIONS: Despite the important consequences of iodine deficiency for pregnant women and the recommendations of many medical societies, the majority of U.S. obstetricians and midwives who participated in this survey do not recommend iodine-containing vitamins in women planning pregnancy, during pregnancy, and during lactation.

Iodine deficiency amongst pregnant women in South-West England.

INTRODUCTION: Iodine deficiency in pregnancy may impair foetal neurological development. The UK population is generally thought to be iodine sufficient; however, recent studies have questioned this assumption. Our study aimed to explore the prevalence of iodine deficiency in a cohort of pregnant mothers from South-West England. METHODS: Urine samples were obtained from 308 women participating in a study of breech presentation in late pregnancy. They had no known thyroid disease and a singleton pregnancy at 36-38 weeks' gestation. Samples were analysed for urinary iodine concentrations (UIC). Baseline data included age, parity, smoking status, ethnicity, body mass index (BMI) at booking, prenatal vitamin use and a dietary questionnaire. There was no difference in median UIC between women with (n = 156) or without (n = 152) a breech presentation (P = 0·3), so subsequent analyses were carried out as a combined group. RESULTS: Participants had a mean (SD) age 31(5) years, median (IQR) BMI 24·4 (22·0, 28·3) kg/m2 ; 42% were primiparous, 10% smoked during pregnancy, and 35% took iodine-containing vitamins. Ninety-six per cent were Caucasian. Median (IQR) UIC was 88·0 (54·3, 157·5) µg/l, which is consistent with iodine deficiency by WHO criteria. A total of 224/308 (73%) of women had UIC values <150 µg/l. Increasing milk intake was associated with higher UIC (P = 0·02). There was no difference in median (IQR) UIC between those women who took iodine-containing vitamins (n = 108) and those who did not (n = 200): 88 (54, 168) vs 88 (54, 150) µg/l, P = 0·7. CONCLUSION: Iodine deficiency in pregnancy is common in South-West England. Measures to develop optimum prevention and treatment strategies are urgently needed.

No difference in urinary iodine concentrations between Boston-area breastfed and formula-fed infants.

BACKGROUND: Thyroid hormone is essential for normal mental and physical development in infancy and childhood and is dependent on adequate iodine intake. During the first few months of life, infants are reliant on breastmilk and/or infant formula as their sole sources of dietary iodine. The iodine status of U.S. infants has not been well studied. METHODS: This was a cross-sectional study of 95 breastfed and/or formula-fed infants less than 3 months of age in the Boston area. We measured iodine content from infants' single spot urine samples and assessed associations with infant feeding type as well as maternal demographic data, salt and multivitamin use, smoking status, and diet. RESULTS: The median infant urine iodine concentration was 197.5 µg/L (range 40-897.5 µg/L). Median infant urine iodine concentrations were similar between infants who were exclusively breastfed (n=39, 203.5 µg/L; range 61.5-395.5 µg/L), formula-fed (n=44, 182.5 µg/L; range 40-897.5 µg/L), and mixed (n=10, 197.8 µg/L; range 123-592.5) (p=0.88). There were no significant correlations of infant urinary iodine with maternal salt or multivitamin use (regularly or in the past 24 hours), active or secondhand cigarette smoke exposures, infant weight, infant length, or recent maternal ingestion of common iodine-containing foods, although the correlations with iodine-containing foods are difficult to accurately determine due to the small sample sizes of these variables. CONCLUSIONS: Both breastfed and formula-fed infants less than 3 months of age in the Boston area were generally iodine sufficient. Larger studies are needed to confirm these observations among infants nationwide and elucidate other factors that may contribute to infant iodine nutrition.

Long-term efficacy of modified-release recombinant human thyrotropin augmented radioiodine therapy for benign multinodular goiter: results from a multicenter, international, randomized, placebo-controlled, dose-selection study.

BACKGROUND: Enhanced reduction of multinodular goiter (MNG) can be achieved by stimulation with recombinant human thyrotropin (rhTSH) before radioiodine ((131)I) therapy. The objective was to compare the long-term efficacy and safety of two low doses of modified release rhTSH (MRrhTSH) in combination with (131)I therapy. METHODS: In this phase II, single-blinded, placebo-controlled study, 95 patients (57.2 ± 9.6 years old, 85% women, 83% Caucasians) with MNG (median size 96.0 mL; range 31.9-242.2 mL) were randomized to receive placebo (n=32), 0.01 mg MRrhTSH (n=30), or 0.03 mg MRrhTSH (n=33) 24 hours before a calculated (131)I activity. Thyroid volume (TV) and smallest cross-sectional area of trachea (SCAT) were measured (by computed tomography scan) at baseline, six months, and 36 months. Thyroid function and quality of life (QoL) was evaluated at three-month and yearly intervals respectively. RESULTS: At six months, TV reduction was enhanced in the 0.03 mg MRrhTSH group (32.9% vs. 23.1% in the placebo group; p=0.03) but not in the 0.01 mg MRrhTSH group. At 36 months, the mean percent TV reduction from baseline was 44 ± 12.7% (SD) in the placebo group, 41 ± 21.0% in the 0.01 mg MRrhTSH group, and 53 ± 18.6% in the 0.03 mg MRrhTSH group, with no statistically significant differences among the groups, p=0.105. In the 0.03 mg MRrhTSH group, the subset of patients with basal (131)I uptake <20% had a 24% greater TV reduction at 36 months than the corresponding subset of patients in the placebo group (p=0.01). At 36 months, the largest relative increase in SCAT was observed in the 0.03 mg MRrhTSH group (13.4 ± 23.2%), but this was not statistically different from the increases observed in the placebo or the 0.01 mg MRrhTSH group (p=0.15). Goiter-related symptoms were reduced and QoL improved, without any enhanced benefit from using MRrhTSH. At three years, the prevalence of permanent hypothyroidism was 13%, 33%, and 45% in the placebo, 0.01 mg, and 0.03 mg MRrhTSH groups respectively. The overall safety profile of the study was favorable. CONCLUSIONS: When used as adjuvant to (131)I, enhanced MNG reduction could not be demonstrated with MRrhTSH doses ≤ 0.03 mg, indicating that the lower threshold for efficacy is around this level.

Iodine concentration in commercial cat foods from three regions of the USA, 2008-2009.

Fluctuations in iodine concentration in food have been suggested as one risk factor for the development of feline hyperthyroidism, an epidemic disease first described in 1979. Three international studies have examined iodine concentrations of commercial cat foods. The iodine concentration of 112 commercial cat foods from across the USA was measured, and the daily iodine intake by hypothetical 4.5 kg adult cats or 1.4 kg kittens calculated in this descriptive epidemiologic study to examine differences in feline iodine intake due to (i) geographical source of foods, (ii) packaging type, (iii) brand-to-brand variation, (iv) form of iodine supplementation, (v) types and numbers of seafood ingredients and (vi) kitten and 'therapeutic' diets. Dramatic variation among canned foods (resulting in ingestion of approximately 49-9639 µg iodine/day) suggests that the disparity in iodine concentrations may lead to development of nodular hyperplasia and, later, clinical hyperthyroidism, if cats consume diets that are at first iodine-deficient and later contain excessive iodine. Manufacturers are encouraged to ensure adequate iodine supplementation across all products and areas of the USA.

History of U.S. iodine fortification and supplementation.

Iodine is a micronutrient required for thyroid hormone production. This review highlights the history of the discovery of iodine and its uses, discusses the sources of iodine nutrition, and summarizes the current recommendations for iodine intake with a focus on women of childbearing age.

Congenital hypothyroidism caused by excess prenatal maternal iodine ingestion.

We report the cases of 3 infants with congenital hypothyroidism detected with the use of our newborn screening program, with evidence supporting excess maternal iodine ingestion (12.5 mg/d) as the etiology. Levels of whole blood iodine extracted from their newborn screening specimens were 10 times above mean control levels. Excess iodine ingestion from nutritional supplements is often unrecognized.

Iodine-induced thyroid dysfunction.

PURPOSE OF REVIEW: To summarize the mechanisms of iodine-induced hypothyroidism and hyperthyroidism, identify the risk factors for thyroid dysfunction following an iodine load, and summarize the major sources of excess iodine exposure. RECENT FINDINGS: Excess iodine is generally well tolerated, but individuals with underlying thyroid disease or other risk factors may be susceptible to iodine-induced thyroid dysfunction following acute or chronic exposure. Sources of increased iodine exposure include the global public health efforts of iodine supplementation, the escalating use of iodinated contrast radiologic studies, amiodarone administration in vulnerable patients, excess seaweed consumption, and various miscellaneous sources. SUMMARY: Iodine-induced thyroid dysfunction may be subclinical or overt. Recognition of the association between iodine excess and iodine-induced hypothyroidism or hyperthyroidism is important in the differential diagnosis of patients who present without a known cause of thyroid dysfunction.

Low iodine content in the diets of hospitalized preterm infants.

CONTEXT: Iodine is critical for normal thyroid hormone synthesis and brain development during infancy, and preterm infants are particularly vulnerable to the effects of both iodine deficiency and excess. Use of iodine-containing skin antiseptics in intensive care nurseries has declined substantially in recent years, but whether the current dietary iodine intake meets the requirement for hospitalized preterm infants is unknown. OBJECTIVE: The aim of the study was to measure the iodine content of enteral and parenteral nutrition products commonly used for hospitalized preterm infants and estimate the daily iodine intake for a hypothetical 1-kg infant. METHODS: We used mass spectrometry to measure the iodine concentration of seven preterm infant formulas, 10 samples of pooled donor human milk, two human milk fortifiers (HMF) and other enteral supplements, and a parenteral amino acid solution and soy-based lipid emulsion. We calculated the iodine provided by typical diets based on 150 ml/kg · d of formula, donor human milk with or without HMF, and parenteral nutrition. RESULTS: Preterm formula provided 16.4-28.5 µg/d of iodine, whereas unfortified donor human milk provided only 5.0-17.6 µg/d. Adding two servings (six packets) of Similac HMF to human milk increased iodine intake by 11.7 µg/d, whereas adding two servings of Enfamil HMF increased iodine intake by only 0.9 µg/d. The other enteral supplements contained almost no iodine, nor did a parenteral nutrition-based diet. CONCLUSIONS: Typical enteral diets for hospitalized preterm infants, particularly those based on donor human milk, provide less than the recommended 30 µg/d of iodine, and parenteral nutrition provides almost no iodine. Additional iodine fortification should be considered.

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.

Iodine status and thyroid function of Boston-area vegetarians and vegans.

CONTEXT: Adequate dietary iodine is required for normal thyroid function. The iodine status and thyroid function of U.S. vegetarians and vegans have not been previously studied. Environmental perchlorate and thiocyanate (inhibitors of thyroid iodine uptake) exposures may adversely affect thyroid function. OBJECTIVE: The objective of the study was to assess the iodine status and thyroid function of U.S. vegetarians (consume plant based products, eggs, milk; abstain from meat, poultry, fish, shellfish) and vegans (avoid all animal products) and whether these may be affected by environmental perchlorate and thiocyanate exposures. DESIGN AND SETTING: This was a cross-sectional assessment of urinary iodine, perchlorate, and thiocyanate concentrations and serum thyroid function in Boston-area vegetarians and vegans. SUBJECTS: One hundred forty-one subjects (78 vegetarians, 63 vegans) were recruited; one vegan was excluded. RESULTS: Median urinary iodine concentration of vegans (78.5 µg/liter; range 6.8-964.7 µg/liter) was lower than vegetarians (147.0 µg/liter; range 9.3-778.6 µg/liter) (P < 0.01). Adjusted for cigarette smoking (confirmed by urinary cotinine levels) and thiocyanate-rich food consumption, median urinary thiocyanate concentration of vegans (630 µg/liter; range 108-3085 µg/liter) was higher than vegetarians (341 µg/liter; range 31-1963 µg/liter) (P < 0.01). There were no between-group differences in urinary perchlorate concentrations (P = 0.75), TSH (P = 0.46), and free T(4) (P = 0.77). Urinary iodine, perchlorate, and thiocyanate levels were not associated with TSH (P = 0.59) or free T(4) (P = 0.14), even when adjusted for multiple variables. CONCLUSIONS: U.S. vegetarians are iodine sufficient. U.S. vegans may be at risk for low iodine intake, and vegan women of child-bearing age should supplement with 150 µg iodine daily. Environmental perchlorate and thiocyanate exposures are not associated with thyroid dysfunction in these groups.

Colostrum iodine and perchlorate concentrations in Boston-area women: a cross-sectional study.

OBJECTIVE: To measure levels of colostrum iodine, which has not been previously measured, and perchlorate and cotinine (a surrogate for thiocyanate derived from cigarette smoke) in women up to 60 h postpartum. Perchlorate and thiocyanate are environmental inhibitors of iodide transport into the thyroid and lactating breast. DESIGN: Cross-sectional. PATIENTS: Ninety seven postpartum women in Boston, Massachusetts, USA. MEASUREMENTS: Colostrum iodine and perchlorate, and spot urine iodine, perchlorate, cotinine and creatinine concentrations were measured. RESULTS: Sufficient colostrum was obtained to measure iodine in 61 samples and perchlorate in 46 samples. Median colostrum iodine content was 51.4 micromol/l (range 21.3-304.2 microg/l). Perchlorate was detectable in 43 of 46 colostrum samples (median 2.5 micromol/l; range, < 0.05-188.9 micromol/l). Median urine iodine in 97 samples was 82.2 micromol/l (range, 10.3-417.1 micromol/l). Perchlorate was detectable in all 97 urine samples (median 2.6 micromol/l; range, 0.2-160.6 micromol/l). Colostrum iodine content was not significantly correlated with levels of colostrum perchlorate or concentrations per litre of urinary iodine, perchlorate, or cotinine. Colostrum perchlorate concentrations were not significantly associated with urinary iodine, perchlorate, or cotinine levels. Urinary cotinine levels were not significantly associated with urinary iodine or perchlorate levels. There was no association between maternal urinary iodine and urinary perchlorate levels. CONCLUSIONS: Iodine is present in human colostrum and thus available for breastfeeding infants immediately after birth. Perchlorate was also present in 93% of samples measured, but the concentrations did not correlate with colostrum iodine concentrations.

Association of first-trimester thyroid function test values with thyroperoxidase antibody status, smoking, and multivitamin use.

OBJECTIVE: To determine first-trimester thyroid function values and associations with thyroperoxidase antibody (TPO-Ab) status, smoking, emesis, and iodine-containing multivitamin use. METHODS: We collected information by interview, questionnaire, and blood draw at the initial obstetric visit in 668 pregnant women without known thyroid disease. We compared thyroid-stimulating hormone (TSH), total thyroxine (T4), and free T4 index (FT4I) values by TPO-Ab status. Multiple regression was used to identify characteristics associated with thyroid function values. RESULTS: The following median (range containing 95% of the data points) thyroid function test values were obtained in 585 TPO-Ab-negative women: TSH, 1.1 mIU/L (0.04-3.6); FT4I, 2.1 (1.5-2.9); and T4, 9.9 microg/dL (7.0-14.0). The following median (range containing 95% of the data points) thyroid function test values were obtained in 83 TPO-Ab-positive women: TSH, 1.8 mIU/L (0.3-6.4) (P<.001); FT4I, 2.0 (1.4-2.7) (P = .06); and T4, 9.3 microg/dL (6.8-13.0) (P = .03) (P values denote statistically significant differences between TPO-Ab-positive and negative participants). Among TPO-Ab-negative participants, TSH level was not associated with use of iodine-containing multivitamins, smoking, or race. TSH increased 0.03 mIU/L for every year of maternal age (P = .03) and decreased by 0.3 mIU/L for every increase in parity (P<.001). T4 decreased 0.04 microg/dL for every year of maternal age (P = .04). Mean FT4I was 2.05 in smokers and 2.20 in nonsmokers (P<.01). There were no relationships between T4 or FT4I and parity, race, or iodine-containing multivitamin use. CONCLUSION: TPO-Ab status of pregnant women should be considered when constructing trimester-specific reference ranges because elevated serum TPO-Ab levels are associated with higher TSH and lower T4 values.

Seaweed and soy: companion foods in Asian cuisine and their effects on thyroid function in American women.

Seaweeds and soy are two commonly eaten foods in Asia. Both have been reported to affect thyroid function, seaweed because of its iodine content and soy because of its goitrogenic effect. Twenty-five healthy postmenopausal women (mean age 58 years) completed a double-blinded randomized crossover study. Ten capsules (5 g/day) of placebo or seaweed (Alaria esculenta), providing 475 microg of iodine/day, were consumed daily for 7 weeks. A powdered soy protein isolate (Solae Co., St. Louis, MO), providing 2 mg of isoflavones/kg of body weight, was given daily during the last week of each treatment arm. On average, this provided 141.3 mg of isoflavones/day and 67.5 g of protein/day. Blood samples and 48-hour urine samples were collected before and after each intervention period, and urinary I/C (microg of iodine/g of creatinine) and serum thyroxine, free thyroxine index, total triiodothyronine, and thyroid stimulating hormone (TSH) were measured. Seaweed ingestion increased I/C concentrations (P < .0001) and serum TSH (P < .0001) (1.69 +/- 0.22 vs. 2.19 +/- 0.22 microU/mL, mean +/- SE). Soy supplementation did not affect thyroid end points. Seven weeks of 5 g/day seaweed supplementation was associated with a small but statistically significant increase in TSH. Soy protein isolate supplementation was not associated with changes in serum thyroid hormone concentrations.