Iodine in human milk: perspectives for infant health

The use of breast milk iodine concentration in the first week of lactation as a biomarker of iodine status in breast-feeding women

Breast milk iodine concentration (BMIC) is a promising indicator of iodine status in lactating women. However, there are limited data on its usefulness to reflect maternal iodine deficiency. Therefore, the aim of our study was to assess iodine concentration in breast milk and urine samples in exclusively breast-feeding women. Eligible pregnant women undergoing routine antenatal care in a large hospital in Shaanxi Province, China, were followed up from the third trimester of pregnancy until the first week of lactation. Urine samples (20 ml) were collected during pregnancy and lactation. Iodine concentration in samples was measured based on Sandell-Kolthoff reaction. Breast milk samples (5 ml) were provided during lactation. A receiver operating curve (ROC) was constructed to determine the diagnostic performance of BMIC. An iodine-specific FFQ was completed twice during pregnancy and lactation. A total of 200 women completed the study. The overall median BMIC was 89 μg/l, indicating iodine sufficiency (i.e. BMIC reference range between 60 and 465 μg/l). Women reported similar median urinary iodine concentration (UIC) during pregnancy and lactation (112 and 113 μg/l, respectively), but their iodine status differed - mild-to-moderate iodine deficiency during pregnancy and iodine sufficiency during lactation. The ROC for BMIC using UIC as a reference standard was 0·755 (95 % CI: 0·644, 0·866). In conclusion, this study demonstrated that women were iodine sufficient in the first week of lactation as assessed by UIC, which was consistent with BMIC. These findings suggested that BMIC is a useful biomarker to assess iodine status in lactating women.

Iodine: a scoping review for Nordic Nutrition Recommendations 2023

Iodine is essential for the synthesis of the thyroid hormones thyroxine (T4) and triiodothyronine (T3). As in many other parts of the world, insufficient iodine intake and consequently insufficient iodine status is a public health challenge in the Nordic and Baltic countries. The main dietary sources of iodine in the Nordic and Baltic countries include cow's milk, saltwater fish, eggs, products containing iodised salt, and iodised table salt. Only Denmark (DK), Finland (FI) and Sweden (SE) have implemented mandatory (DK) or voluntary (SE, FI) salt iodisation. New data, as well as recent studies from the Nordic and Baltic countries, strengthen the evidence that the main health challenges related to insufficient iodine intake remain thyroid function and thyroid disease, mental development, and cognitive function. Excessive intakes can also cause hyperthyroidism, autoimmune thyroid disease, and thyroid cancer.

Assessment of the Iodine Status of Lactating Women and Infants in Shanghai, China

There is a risk of iodine deficiency among pregnant women in China. However, research on the iodine status of lactating women and infants is scarce. In this study, we aimed to evaluate the iodine status of lactating women and their infants and explore the relationship between breast milk iodine concentrations (BMICs) and urinary iodine concentrations (UICs). In total, 257 lactating women and their infants were recruited from the Shanghai Sixth People's Hospital East campus between May 2018 and May 2019. The BMIC and UIC were measured by inductively coupled plasma‒mass spectrometry (ICP‒MS). One-day 24-h dietary recall was used to determine the dietary intake of iodine. The mean dietary intake of iodine among the lactating women was 145.1 μg/day, and 97.83% (n = 225) of the lactating women had a dietary iodine intake below 240 μg/day. The median BMIC and UIC of the lactating women was 150.7 μg/L (interquartile range, IQR 102.9, 205.5) and 110.0 μg/L (IQR 65.8, 171.4), respectively, and the median UIC of the infants was 212.7 μg/L (IQR 142.1, 320.6). The BMIC of lactating women who consumed iodized salt was significantly higher than that of lactating women who did not consume iodized salt (p = 0.015). The infants' UIC values were significantly correlated with the BMIC values (r = 0.597**, p < 0.001). The iodine nutritional status of lactating women and infants in Shanghai was generally sufficient according to the WHO's iodine nutritional status recommendation. The use of iodized salt was related to increasing dietary iodine intake and the BMIC. Improvements in BMICs have positive effects on the nutritional levels of iodine in infants.

Iodine Concentration in the Breast Milk and Urine as Biomarkers of Iodine Nutritional Status of Lactating Women and Breastfed Infants in Taiwan

Breast milk iodine concentration (BMIC) can be different when median urinary iodine concentration (UIC) is similar. The BMIC, UIC/creatinine (Cr), estimated 24-h urinary iodine excretion (24-h UIE) of lactating women in Taiwan is unknown. This study enrolled lactating women from Taipei Veterans General Hospital (August 2021-February 2023). Each participant provided a random spot urine sample, two breast milk samples, a blood sample, and completed a food frequency questionnaire on the same day. Iodine measurement was performed by inductively coupled plasma mass spectrometry. The median UIC of the enrolled 71 women was 91.1 μg/L, indicating insufficient iodine status; however, the median BMIC was 166.6 μg/L and this suggested that the amount of iodine delivered through breast milk was adequate for the breastfed infants. BMIC was correlated with UIC/Cr and 24-h UIE (both rs = 0.49) but not with UIC (rs = 0.18) or thyroid stimulating hormone (rs = 0.07). Women who did not consume dairy products (adjusted odds ratio: 24.41, 95% confidence interval: 1.26-471.2) and multivitamins (adjusted odds ratio: 8.26, 95% confidence interval: 1.76-38.79) were at increased odds for having lower BMIC. The results suggest that measuring maternal UIC alone may not be sufficient, as BMIC, UIC/Cr, and 24-h UIE are all important biomarkers. Ingestion of dairy products and multivitamins were independently associated with BMIC.

Associations of Dietary Intake and Nutrient Status with Micronutrient and Lipid Composition in Breast Milk of Donor Women

The influence of the diet and nutritional status of milk donors on the nutritional composition of donor human milk (DHM) is unknown. The present study aimed to determine the nutritional profile of DHM and the associations between donors' dietary intake and nutritional status and the micronutrient and lipid composition in DHM. For this purpose, 113 donors completed a food frequency questionnaire, provided a five-day weighed dietary record, and collected milk for five consecutive days. Nutrient determinations in donors' erythrocytes, plasma, urine, and milk were performed. Multiple linear regressions were conducted for the evaluation of the associations. We highlight the following results: DHM docosahexaenoic acid (DHA) was positively associated with donors' plasma DHA content and donors' DHA intake (R2 0.45, p < 0.001). For every 1 g/day DHA intake, an increase of 0.38% in DHA content and 0.78% in total omega-3 content was observed in DHM (R2 0.29, p < 0.001). DHM saturated fatty acids were positively associated with erythrocyte dimethyl acetals, plasma stearic acid, trans fatty acids intake, and breastfeeding duration and negatively associated with erythrocyte margaroleic acid (R2 0.34, p < 0.01). DHM cholecalciferol was associated with plasma cholecalciferol levels and dairy intake (R2 0.57, p < 0.01). Other weaker associations were found for free thiamin, free riboflavin, pyridoxal, dehydroascorbic acid, and the lipid profile in DHM. In conclusion, the diet and nutritional status of donors influence the fatty acid profile and micronutrient content of DHM.

Iodine Metabolism and Thyroid Function During the Perinatal Period: Maternal-Neonatal Correlation and Effects of Topical Povidone-Iodine Skin Disinfectants

An adequate maternal iodine intake during pregnancy and lactation is essential for growth and mental development in fetuses and newborns. There are limited data on perinatal iodine metabolism in mothers and infants, as well as the effect of povidone-iodine (PVP-I) antiseptics used in cesarean delivery. The urinary iodine concentration (UIC), serum iodine, thyrotropin (TSH), free thyroxine (FT4), and breast milk iodine concentration (BMIC) were measured consecutively in a total of 327 mothers and 249 term-infants in two prospective studies. The maternal median UIC was 164 μg/L in the third trimester, increased to 256 μg/L at 44 h after birth, and then decreased to 116 μg/L 1 month later. The BMIC on the 4th and 32th postpartum days was 17.6 and 13.5 μg/100 g, respectively. In neonatal infants born to the mothers unexposed to PVP-I, the median UIC was 131 μg/L in the first voiding urine and increased to 272 μg/L on day 4 and then slightly decreased to 265 μg/L on day 28 suggesting sufficient iodine reserve at birth. PVP-I antiseptics containing 1 g of iodine for skin preparation at cesarean delivery transiently increased maternal serum iodine concentration (1.9-fold), UIC (7.8-fold) at 41 h after surgery and BMIC, while it had little effect on maternal TSH, FT4, and neonatal UIC, TSH, or FT4. The iodine status of pregnant women and their infants was adequate in this population; however, the UIC in lactating mothers at one postpartum month was low enough to suggest iodine deficiency or near iodine deficiency. Further studies are necessary.

Human Milk Composition and Nutritional Status of Omnivore Human Milk Donors Compared with Vegetarian/Vegan Lactating Mothers

Women of childbearing age in Western societies are increasingly adopting vegetarian diets. These women are sometimes rejected as milk donors, but little about the composition of their milk is known. The present study aimed to compare the intake, nutritional status, and nutritional composition of human milk from omnivore human milk donors (Donors) and vegetarian/vegan lactating mothers (Veg). Milk, blood, and urine samples from 92 Donors and 20 Veg were used to determine their fatty acid profiles, as well as vitamins and minerals. In a representative sample of both groups, we also determined the lipid class profile as a distribution of neutral and polar lipids, the molecular species of triacylglycerols, and the relative composition of phospholipids in their milk. A dietary assessment was conducted with a five-day dietary record (while considering the intake of supplements). We highlight the following results, expressed as the mean (SE), for the Veg vs. Donors: (1) Their docosahexaenoic acid (DHA) intake was 0.11 (0.03) vs. 0.38 (0.03) g/day; the plasma DHA was 0.37 (0.07) vs. 0.83 (0.06)%; and the milk DHA was 0.15 (0.04) vs. 0.33 (0.02)%. (2) Their milk B12 levels were 545.69 (20.49) vs. 482.89 (4.11) pM; 85% of the Veg reported taking B12 supplements (mean dose: 312.1 mcg/day); and the Veg group showed no differences with Donors in terms of total daily intake or plasma B12. (3) Their milk phosphatidylcholine levels were 26.88 (0.67) vs. 30.55 (1.10)%. (4) Their milk iodine levels were 126.42 (13.37) vs. 159.22 (5.13) mcg/L. In conclusion, the Vegs' milk was shown to be different from the Donors' milk, mainly due to its low DHA content, which is concerning. However, raising awareness and ensuring proper supplementation could bridge this gap, as has already been achieved for cobalamin.

Inadequate Iodine Intake in Mothers of Young Children in Innlandet County, Norway

Background

Iodine has an essential role in child growth and brain development. Thus, sufficient iodine intake is particularly important in women of childbearing age and lactating women.

Objectives

This cross-sectional study aimed to describe iodine intake in a large random sample of mothers of young children (aged ≤2 y) living in Innlandet County, Norway.

Methods

From November 2020 to October 2021, 355 mother-child pairs were recruited from public health care centers. Dietary data were obtained using two 24-h dietary recalls (24-HRs) per woman and an electronic FFQ. The Multiple Source Method was used to estimate the usual iodine intake from the 24-HR assessment.

Results

Based on the 24-HRs, the median (P25, P75) usual iodine intake from food was 117 μg/d (88, 153) in nonlactating women and 129 μg/d (95, 176) in lactating women. The median (P25, P75) total usual iodine intake (from food combined with supplements) was 141 μg/d (97, 185) in nonlactating women and 153 μg/d (107, 227) in lactating women. Based on the 24-HRs, 62% of the women had a total iodine intake below the recommendations (150 μg/d in nonlactating women and 200 μg/d in lactating women), and 23% of them had an iodine intake below the average requirement (100 μg/d). The reported use of iodine-containing supplements was 21.4% in nonlactating women and 28.9% in lactating women. In regular users of iodine-containing supplements (n = 63), supplements contributed to an average of 172 μg/d of iodine. Among regular iodine supplement users, 81% reached the recommendations compared with 26% of nonsupplement users (n = 237). The iodine intake estimated by FFQ was substantially higher than that estimated by 24-HRs.

Conclusions

Maternal iodine intake in Innlandet County was inadequate. This study confirms the need for action to improve iodine intake in Norway, particularly among women of childbearing age.

Estimation of appropriate dietary intake of iodine among lactating women in China based on iodine loss in breast milk

OBJECTIVE

Data on iodine loss in breast milk, which are critical for establishing the appropriate dietary iodine intake for lactating women, is currently limited. A study was conducted to assess iodine loss in breast milk among Chinese lactating women to estimate the appropriate dietary intake of iodine.

METHODS

A total of 54 pairs of healthy, lactating women and their infants aged 0-6 months were recruited from Tianjin and Luoyang cities in China. A 4 days infant weighing study was conducted to assess iodine loss in the breast milk of lactating women. Mothers were required to weigh and record their infants' body weights before and after each feeding for a 24 h period from 8:00 am to 8:00 am. During the weighing study, 2812 breast milk samples and 216 24-h urine samples were collected from each lactating mother for four consecutive days. In addition, a 3 days 24 h dietary record, including salt weighing and drinking water samples collecting, was performed by each lactating mother to determine dietary iodine intake during the weighing study.

RESULTS

The average dietary iodine intake of lactating women was 323 ± 80 μg/d. The median breast milk iodine concentration and 24 h urinary iodine concentration of lactating women were 154 (122-181) and 135 (104-172) μg/L, respectively. The mean volume of breast milk and the mean iodine loss in the breast milk of lactating women were 711 ± 157 mL/d and 112 ± 47 μg/d, respectively. The appropriate dietary intake of iodine among lactating Chinese women is approximately 260 µg/d.

CONCLUSIONS

Based on the iodine loss in breast milk (110 μg/d) found in this study, and the estimated average requirement of iodine for adults, the appropriate dietary intake of iodine among lactating Chinese women is 260 µg/d, which is higher than the 240 μg/d recommended by the China Nutrition Science Congress in 2013.

Iodine Deficiency of Breastfeeding Mothers and Infants from 2012 to 2019 in Zhengzhou, China

To investigate iodine status and characteristics of breastfeeding women and infants in Zhengzhou after the implementation of the new national standard of iodine in edible salt, so as to provide the basis for formulating prevention and control measures. Urine samples from 28,730 infants aged 0-2 years and 17,977 breastfeeding women who received preventive health care in 12 districts/cities of Zhengzhou from 2012 to 2019 were collected to measure urinary iodine concentration (UIC). A total of 350 pairs of unweaned infants and their mothers were included in this study. After the implementation of the new national standard of iodine in edible salt, the iodine deficiency of infants aged 0-2 years showed a trend of decreasing first and then increasing, but generally the iodine nutrition of infants aged 0-2 years was at the appropriate level in 8 years. There was a gradual decrease in iodine deficiency among breastfeeding women over an 8-year period. And the median UIC of breastfeeding women in 8 years was at iodine nutrition appropriate level. In addition, the UIC of breastfeeding mothers was positively associated with that of infants (r = 0.104, P = 0.004). After the implementation of the new national standard of iodine in edible salt, breastfeeding women and infants in Zhengzhou generally were at an appropriate level of iodine nutrition, and there was a significant positive correlation between the UIC of breastfeeding mothers and infants.

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.

Assessment of Iodine Concentration in Human Milk from Donors: Implications for Preterm Infants

Preterm infants are particularly vulnerable to developing iodine deficiency. Donor human milk (DHM) is the preferred feeding option if the mother’s own milk (MOM) is not available, but information on DHM iodine concentration (DHMIC) is lacking. Hence, we aimed to assess DHMIC to further evaluate the adequacy of iodine provision in preterm infants. Finally, associations that might influence DHMIC were studied. In 113 donors, we measured iodine intake by evaluating dietary records for five consecutive days with the DIAL® Software. From the second day of dietary record, donors provided human milk samples (at least one per day) for four consecutive days. Daily human milk samples were analyzed for DHMIC. A DHMIC ≥ 200 µg/L was considered an adequate iodine content for preterm infants. DHMIC and urine iodine concentration (UIC) were determined using ICP-MS. In our study, 83.2% of donors had a full-term infant. Breastfeeding time range was 1.5−49.4 months. During the dietary record, 55.8% took iodine-containing supplements, providing 40−200 µg/day of iodine. The medians (p25, p75) UIC and DHMIC were 112.4 (75.8, 160.1) and 148.5 (97.6, 206.1) µg/L, respectively. In this iodine-sufficient population, 70% had a DHMIC of <200 µg/L. Donors’ intake of iodine-containing supplements was associated with higher DHMIC.

Mechanisms of Sodium/Iodide Symporter-Mediated Mammary Gland Iodine Compensation during Lactation

This research aimed to investigate the compensation mechanism of iodine deficiency and excess in the mammary gland during lactation. Female rats were divided into the low iodine group (LI), the normal iodine group (NI), the 10-fold high iodine group (10HI) and the 50-fold high iodine group (50HI). We measured the iodine levels in the urine, blood, milk, and mammary gland. The protein expression of sodium/iodide symporter (NIS), DPAGT1, and valosin-containing protein (VCP) in the mammary gland was also studied. The 24-hour urinary iodine concentration, serum total iodine concentration, serum non-protein-bound iodine concentration, breast milk iodine concentration, and mammary gland iodine content in the 50HI group were significantly higher than those in the NI group (p < 0.05). Compared with the NI group, NIS expression in the 50HI group significantly decreased (p < 0.05). DAPGT1 expression was significantly higher in the LI group than in the NI group (p < 0.05). The expression level of VCP was significantly increased in the 10HI and 50HI groups. In conclusion, milk iodine concentration is positively correlated with iodine intake, and the lactating mammary gland regulates the glycosylation and degradation of NIS by regulating DPAGT1 and VCP, thus regulating milk iodine level. However, the mammary gland has a limited role in compensating for iodine deficiency and excess.

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.

Improving Iodine Status in Lactating Women: What Works?

PURPOSE OF REVIEW

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

RECENT FINDINGS

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

Breast Milk Micronutrients and Infant Neurodevelopmental Outcomes: A Systematic Review

Micronutrients are fundamental for healthy brain development and deficiencies during early development can have a severe and lasting impact on cognitive outcomes. Evidence indicates that undernourished lactating individuals may produce breast milk containing lower concentrations of certain vitamins and minerals. Exclusively breastfed infants born to mothers deficient in micronutrients may therefore be at risk of micronutrient deficiencies, with potential implications for neurodevelopment. This systematic review aims to consider current knowledge on the effects of breast milk micronutrients on the developmental outcomes of infants. The databases Medline, Global Health, PsychInfo, Open Grey, and the Web of Science were searched for papers published before February 2021. Studies were included if they measured micronutrients in breast milk and their association with the neurodevelopmental outcomes of exclusively breastfed infants. Also, randomised control trials investigating neurocognitive outcomes following maternal supplementation during lactation were sought. From 5477 initial results, three observational studies were eligible for inclusion. These investigated associations between breast milk levels of vitamin B6, carotenoids, or selenium and infant development. Results presented suggest that pyroxidal, β-carotene, and lycopene are associated with infant neurodevelopmental outcomes. Limited eligible literature and heterogeneity between included papers prevented quantitative synthesis. Insufficient evidence was identified, precluding any conclusions on the relationship between breast milk micronutrients and infant developmental outcomes. Further, the evidence available was limited by a high risk of bias. This highlights the need for further research in this area to understand the long-term influence of micronutrients in breast milk, the role of other breast milk micronutrients in infant neurodevelopmental outcomes, and the impact of possible lactational interventions.

Thyroid Gene Mutations in Pregnant and Breastfeeding Women Diagnosed With Transient Congenital Hypothyroidism: Implications for the Offspring's Health

Fetus and infants require appropriate thyroid hormone levels and iodine during pregnancy and lactation. Nature endorses the mother to supply thyroid hormones to the fetus and iodine to the lactating infant. Genetic variations on thyroid proteins that cause dyshormonogenic congenital hypothyroidism could in pregnant and breastfeeding women impair the delivery of thyroid hormones and iodine to the offspring. The review discusses maternal genetic variations in thyroid proteins that, in the context of pregnancy and/or breastfeeding, could trigger thyroid hormone deficiency or iodide transport defect that will affect the proper development of the offspring.

Ingestion of supplements and fortified food with iodine on the breast milk iodine concentration in deficiency areas: a systematic review

Introduction

The level of iodine in breast milk may be inadequate and compromise the health of this, both due to excess and lack, some population groups remain deficient because of the low consumption of iodate salt, because there is an increase in consumption of other sources of iodine, such as supplements and fortified foods.

Objective

To evaluate the effect of the consumption of fortified foods and nutritional supplements with iodine on maternal milk levels.

Methodology

Systematic review based on the Prism method, using the descriptors provided by DeCS. The reading, selection and analysis of the methodological quality of the articles was done by two researchers independently.

Results

From 346 abstracts, 6 were eligible. The median iodination range between the studies ranged from 75 to 600 µg in supplements and 150 and 225 µg in fortified foods with effect on increased iodine concentration of breastmilk (BMIC), achieving the adequacy of the median BMIC in 4 of the 6 studies.

Conclusion

Iodine ingestion through supplements or fortified foods results in improved iodine levels in breast milk.

Use of Iodine Supplements by Breastfeeding Mothers Is Associated with Better Maternal and Infant Iodine Status

Adequate iodine status during conception, pregnancy and lactation is essential for supporting infant neurodevelopment. Iodine status in adults and children was improved after two New Zealand government initiatives, but the status of breastfeeding women is unknown. This study aimed to investigate the iodine intake and status of lactating mother-infant pairs at 3 months postpartum and to assess maternal iodine knowledge and practice. Iodine intake was estimated by a weighed 4-day diet diary (4DDD). Maternal urinary iodine concentrations (UIC) in spot urine, breast milk iodine concentrations (BMIC) and infant UIC were measured. Questions about iodine-specific knowledge and practice were asked. In 87 breastfeeding mother-infant pairs, maternal iodine intake was 151 (99, 285) μg/day, and 58% had an intake below the estimated average requirement (EAR) of 190 μg/day. Maternal median UIC (MUIC) was 82 (46, 157) μg/L indicating iodine deficiency (i.e., < 100 μg/L). Women who used iodine-containing supplements had a significantly higher MUIC (111 vs 68 μg/L, P = 0.023) and BMIC (84 vs 62 μg/L, P < 0.001) than non-users. Infants fed by women using iodine-containing supplements had a higher MUIC (150 vs 86 μg/L, P = 0.036) than those of non-users. A total of 66% (57/87) of women had no or low iodine knowledge. The iodine knowledge score was a statistically significant predictor of consuming iodine-containing supplements [(beta = 1.321, P = 0.008)]. Despite a decade of initiatives to increase iodine intakes in New Zealand, iodine knowledge was low; iodine intake and status of these lactating women were suboptimal, but women who used iodine-containing supplement were more likely to achieve adequate status.Study Registration Number (Australia and New Zealand Clinical Trials Registry): ACTRN12615001028594.

Characterization of Genetic Variants in the SLC5A5 Gene and Associations With Breast Milk Iodine Concentration in Lactating Women of African Descent: The NUPED Study

Background: The sodium iodide symporter is responsible for the transfer of iodine into breast milk and is encoded for by the SLC5A5 gene. The role of genetic variants in the SLC5A5 gene locus in relation to the transfer of iodine from plasma into breast milk in healthy lactating individuals has, to our knowledge, not been explored. Objective: To identify and characterize possible genetic variants of the SLC5A5 gene in women of African descent living in urban South Africa, and to study associations with breast milk iodine concentrations (BMIC) in lactating women. Methods: This study is affiliated to the Nutrition during Pregnancy and Early Development (NuPED) cohort study (n = 250 enrolled pregnant women). In a randomly selected sub-sample of 32 women, the SLC5A5 gene was sequenced to identify known and novel variants. Of the identified variants, genotyping of selected variants was performed in all pregnant women who gave consent for genetic analyses (n = 246), to determine the frequency of the variants in the study sample. Urinary iodine concentration (UIC) in spot urine samples and BMIC were measured to determine iodine status. Associations of SLC5A5 genetic variants with BMIC were studied in lactating women (n = 55). Results: We identified 27 variants from sequencing of gene exomes and 10 variants were selected for further study. There was a significant difference in BMIC between the genotypes of the rs775249401 variant (P = 0.042), with the homozygous GG group having lower BMIC [86.8 (54.9-167.9) μg/L] compared to the (A) allele carriers rs775249401(AG+AA) [143.9 (122.4-169.3) μg/L] (P = 0.042). Of the rs775249401(GG), 49% had UIC <100 μg/L and 61% had BMIC <100 μg/L. On the other hand, 60% of the rs775249401(AG+AA) carriers had UIC <100 μg/L, and none had a BMIC <100 μg/L. Conclusion: Our results suggest that A-allele carriers of rs775249401(AG+AA) are likely to have higher iodine transfer into breast milk compared to the homozygous GG counterparts. Thus, genetic variations in the SLC5A5 gene may play an important role in the transfer of iodine from plasma into breast milk and may partially explain inter-individual variability in BMIC.

Lower educational status interferes with maternal iodine intake during both pregnancy and lactation

OBJECTIVE

To investigate factors affecting conscious iodine intake among pregnant and lactating women in a rural area in Hungary.

METHODS

Pregnant women were studied and followed during lactation. Urinary and breast milk iodine concentration (UIC and MIC) were measured by inductively coupled plasma mass spectrometry. Potential interfering factors, including age, educational status and smoking were assessed.

RESULTS

During pregnancy and lactation, mild iodine deficiency was observed; median UIC were 66 and 49 µg/L, respectively. Educational status was found to be a strong determinant of both iodine nutrition and smoking status during pregnancy (P < 0.01 and P < 0.001) and lactation (P < 0.001 and P < 0.01). While smoking and non-smoking lactating mothers had similar concentrations of urinary iodine (median UIC: 47 and 51 µg/L, P = 0.95), the breast milk of smoking mothers contained less iodine (median MIC: 150 and 203 µg/L, P = 0.03).

CONCLUSIONS

Both low iodine intake and smoking contribute to the higher risk of iodine deficiency in women with lower educational status. In smokers, MIC is often low in spite of normal UIC, presumably due to the iodine transport blocking effect of the cigarette smoke towards breast milk; normal UIC may be misinterpreted as sufficient iodine supply towards the child. Antenatal health promotion strategies should focus on young women with lower educational status, even in regions where sufficient iodine intake has been achieved in non-pregnant adults.

IODINE STATUS AND THYROID FUNCTION IN LACTATING WOMEN AND INFANTS - A SURVEY IN THE ZAGREB AREA, CROATIA

Lactating women (LW) and infants have high dietary iodine requirements and are at risk of iodine deficiency. The aim of the study was to assess iodine status and thyroid function in LW and their breastfed infants in Zagreb, Croatia. The study included 133 LW and breastfed infant pairs. Urinary iodine concentration (UIC) and thyroid function parameters were measured in all subjects. In LW, breast milk iodine concentration (BMIC) was measured and iodine and salt rich food frequency questionnaire data were collected. Results of analysis indicated that 99.2% of the LW used iodized salt in household and 20.4% used iodine-containing vitamin and mineral supplements. Median (IQR) UIC was 75 µg/L (19.0-180.5 µg/L) in LW and 234 µg/L (151.0-367.5 µg/L) in infants, whereas BMIC was 121 µg/kg (87.8-170.8 µg/kg). Multivariate regression analysis revealed BMIC to be a significant predictor of infant UIC (p<0.001). Positive correlation was recorded between LW and infant thyroid function. This was the first study in Croatia demonstrating BMIC to be a reliable biomarker of iodine status during lactation and predicting iodine intake in breastfed infants. The study confirmed that mandatory salt iodization in Croatia ensured sufficient dietary iodine for LW and optimal iodine intake for breastfed infants via breast milk.

Iodine status of postpartum women and their infants aged 3, 6 and 12 months: Mother and Infant Nutrition Investigation (MINI)

To alleviate the re-emergence of iodine deficiency in New Zealand, two strategies, the mandatory fortification of bread with iodised salt (2009) and a government-subsidised iodine supplement for breast-feeding women (2010), were introduced. Few studies have investigated mother and infant iodine status during the first postpartum year; this study aimed to describe iodine status of mothers and infants at 3, 6 and 12 months postpartum (3MPP, 6MPP and 12MPP, respectively). Partitioning of iodine excretion between urine and breast milk of exclusive breast-feeding (EBF) women at 3MPP was determined. In total, eighty-seven mother-infant pairs participated in the study. Maternal and infant spot urinary iodine concentration (UIC) and breast milk iodine concentration (BMIC) were determined. The percentage of women who took iodine-containing supplements decreased from 46 % at 3MPP to 6 % at 12MPP. Maternal median UIC (MUIC) at 3MPP (82 (46, 157) µg/l), 6MPP (85 (43, 134) µg/l) and 12MPP (95 (51, 169) µg/l) were <100 µg/l. The use of iodine-containing supplements increased MUIC and BMIC only at 3MPP. Median BMIC at all time points were below 75 µg/l. Infant MUIC at 3MPP (115 (69, 182) µg/l) and 6MPP (120 (60, 196) µg/l) were below 125 µg/l. Among EBF women at 3MPP, an increased partitioning of iodine into breast milk (highest proportion 60 %) was shown at lower iodine intakes, along with a reduced fractional iodine excretion in urine (lowest proportion 40 %), indicating a protective mechanism for breastfed infants' iodine status. In conclusion, this cohort of postpartum women was iodine-deficient. Iodine status of their breastfed infants was suboptimal. Lactating women who do not consume iodine-rich foods and those who become pregnant again should take iodine-containing supplements.

Inadequate iodine intake in lactating women in Sweden: A pilot 1-year, prospective, observational study

INTRODUCTION

Breastfed infants depend on breast-milk iodine for growth and brain development, as iodine is a trace element important for thyroid hormone production. Iodine need is higher during lactation; hence, mothers and children are at risk of iodine deficiency. We aimed to explore maternal iodine and thyroidal status during lactation.

MATERIAL AND METHODS

Pregnant women were recruited in Gothenburg, southwest Sweden. Maternal urine and serum were collected at pregnancy week 35-37 (n = 84) and 0.5, 4, and 12 months postpartum. Seventy mothers provided breast milk at 0.5 months.

RESULTS

Median (interquartile range) breast-milk iodine concentration was 90 (66-116) μg/L. About 58% had breast-milk iodine concentration <100 μg/L. Iodine supplement users (n = 13) had higher breast-milk iodine concentration than non-users (n = 49) (140 μg/L vs 71 μg/L, P = .001). Exclusively breastfeeding women at 4 months postpartum (n = 57) had lower median urinary iodine concentration (85 μg/L vs 133 μg/L, P = .004) and higher thyroglobulin serum concentration (22.3 μg/L vs 11.8 μg/L, P = .032) than non-exclusively breastfeeding women (n = 25). Concentrations of thyroid hormones were unaffected.

CONCLUSIONS

This pilot study suggests that lactating women in southwest Sweden present mildly inadequate iodine intake, mainly among non-iodine supplement users and exclusively breastfeeding mothers. Studies on the coverage of the iodine fortification program in breastfeeding women are warranted.

Infant drug exposure via breast milk

More than half of women take medications during breastfeeding, predisposing their infants to medication exposure via breast milk. As a result, adverse drug reactions may emerge in the infant, although they are rarely reported. Disposition of maternal drugs in breast milk is described with several key parameters, which include relative infant dose (RID): infant drug intake via milk (weight- and time-adjusted) expressed as a percentage of the similarly adjusted mother's dose. Most drugs show RID values of <10%, indicating that drug concentrations in infant serum do not reach a level known to be therapeutic in adults unless drug clearance is markedly lower than the adult level on a weight basis. RID is a function of milk-to-(maternal) plasma drug concentration ratio (MP ratio) and maternal drug clearance. Therefore, MP ratio between drugs must be interpreted not by itself but with maternal drug clearance of each drug. This is why some drugs such as phenobarbital show an MP ratio of <1 but an RID as high as 50-70%, while morphine shows an MP ratio of 2 but an RID in the range of 5%. Using RID, we interpreted case reports of infant adverse outcomes, and we observed cases with relatively low infant serum concentrations of drug, consistent with low RID, as well as those with near- or above-adult therapeutic serum concentrations, with or without increased drug intake (i.e. high RID). It is important to consider both pharmacokinetic and pharmacodynamic factors in interpreting adverse outcomes in infants breastfed by a mother taking medications.

Current iodine nutrition status in Poland (2017): is the Polish model of obligatory iodine prophylaxis able to eliminate iodine deficiency in the population?

OBJECTIVE

The monitoring of the populations' iodine status is an essential part of successful programmes of iodine deficiency elimination. The current study aimed at the evaluation of current iodine nutrition in school children, pregnant and lactating women as a marker of the effectiveness and sustainability of mandatory iodine prophylaxis in Poland.

DESIGN

The following iodine nutrition indicators were used: urinary iodine concentration (UIC) (all participants) and serum thyroglobulin (pregnant and lactating women).

SETTING

The study was conducted in 2017 within the National Health Programme in five regions of Poland.

PARTICIPANTS

The research included 300 pregnant women, 100 lactating women and 1000 school children (aged 6-12 years).

RESULTS

In pregnant women, median UIC was 111·6 µg/l; there was no significant difference in median UIC according to the region of residence. In 8 % of pregnant women, thyroglobulin level was >40 ng/ml (median thyroglobulin 13·3 ng/ml). In lactating women, median UIC was 68·0 µg/l. A significant inter-regional difference was noted (P = 0·0143). In 18 % of breastfeeding women, thyroglobulin level was >40 ng/ml (median thyroglobulin 18·5 ng/ml). According to the WHO criteria, the investigated sample of pregnant and lactating women was iodine-deficient. Median UIC in school children was 119·8 µg/l (with significant inter-regional variation; P = 0·0000), which is consistent with iodine sufficiency. Ninety-four children (9·4 %) had UIC < 50 µg/l.

CONCLUSIONS

Mandatory iodisation of household salt in Poland has led to a sustainable optimisation of iodine status in the general population. However, it has failed to assure adequate iodine nutrition during pregnancy and lactation.

Genetic and Physiological Factors Affecting Human Milk Production and Composition

Human milk is considered the optimal nutrition for infants as it provides additional attributes other than nutritional support for the infant and contributes to the mother's health as well. Although breastfeeding is the most natural modality to feed infants, nowadays, many mothers complain about breastfeeding difficulties. In addition to environmental factors that may influence lactation outcomes including maternal nutrition status, partner's support, stress, and latching ability of the infant, intrinsic factors such as maternal genetics may also affect the quantitative production and qualitative content of human milk. These genetic factors, which may largely affect the infant's growth and development, as well as the mother's breastfeeding experience, are the subject of the present review. We specifically describe genetic variations that were shown to affect quantitative human milk supply and/or its qualitative content. We further discuss possible implications and methods for diagnosis as well as treatment modalities. Although cases of nutrient-deficient human milk are considered rare, in some ethnic groups, genetic variations that affect human milk content are more abundant, and they should receive greater attention for diagnosis and treatment when necessary. From a future perspective, early genetic diagnosis should be directed to target and treat breastfeeding difficulties in real time.

Effects of Iodine Intake and Nutraceuticals in Thyroidology: Update and Prospects

Iodine is a microelement that is naturally present in some foods, added to others, and available as a dietary supplement [...].

Iodine status of breastfed infants and their mothers' breast milk iodine concentration

Iodine is an essential nutrient for growth and development during infancy. Data on iodine status of exclusively (EBF) and partially breastfed (PBF) infants as well as breast milk iodine concentration (BMIC) are scarce. We aimed to assess (a) infant iodine nutrition at the age of 5.5 months by measuring urinary iodine concentration (UIC) in EBF (n = 32) and PBF (n = 28) infants and (b) mothers' breast milk iodine concentration (n = 57). Sixty mother–infant pairs from three primary health care centres in Reykjavik and vicinities provided urine and breast milk samples for iodine analysis and information on mothers' habitual diet. The mother–infant pairs were participants of the IceAge2 study, which focuses on factors contributing to infant growth and development, including body composition and breast‐milk energy content. The median (25th–75th percentiles) UIC was 152 (79–239) μg/L, with no significant difference between EBF and PBF infants. The estimated median iodine intake ranged from 52 to 86 μg/day, based on urinary data (assuming an average urine volume of 300–500 ml/day and UIC from the present study). The median (25th–75th percentiles) BMIC was 84 (48–114) μg/L. It is difficult to conclude whether iodine status is adequate in the present study, as no ranges for median UIC reflecting optimal iodine nutrition exist for infants. However, the results add important information to the relatively sparse literature on UIC, BMIC, and iodine intake of breastfed infants.

Mild to Moderate Iodine Deficiency and Inadequate Iodine Intake in Lactating Women in the Inland Area of Norway

Breastfed infants are dependent on an adequate supply of iodine in human milk for the production of thyroid hormones, necessary for development of the brain. Despite the importance of iodine for infant health, data on Norwegian lactating women are scarce. We measured iodine intake and evaluated iodine status and iodine knowledge among lactating women. From October to December 2018, 133 mother-infant pairs were recruited in a cross-sectional study through two public health care centers in Lillehammer and Gjøvik. Each of the women provided two human milk specimens, which were pooled, and one urine sample for analysis of iodine concentration. We used 24-hour dietary recall and food frequency questionnaire (FFQ) to estimate short-term and habitual iodine intake from food and supplements. The median (P25, P75) human milk iodine concentration (HMIC) was 71 (45, 127) µg/L-of which, 66% had HMIC <100 µg/L. The median (P25, P75) urinary iodine concentration (UIC) was 80 µg/L (52, 141). The mean (± SD) 24-hour iodine intake and habitual intake was 78 ± 79 µg/day and 75 ± 73 µg/day, respectively. In conclusion, this study confirms inadequate iodine intake and insufficient iodine status among lactating women in the inland area of Norway and medium knowledge awareness about iodine.

Effect of Urinary Iodine Concentration in Pregnant and Lactating Women, and in Their Infants Residing in Areas with Excessive Iodine in Drinking Water in Shanxi Province, China

It is uncertain how many factors affect urinary iodine concentration. The aim of this study was to determine the effect of consumption of drinking water with high iodine concentration on urinary iodine concentration in pregnant and lactating women, and infants. We included 218 lactating women and their infants and 142 pregnant women in areas with suitable and high water iodine content. Urine, serum, and water iodine concentration were assessed. Breastfeeding women living in areas with high water iodine content had a greater likelihood of iodine sufficiency or iodine excess [odds ratio (P = 0.044, P < 0.001)] compared with women living in areas with suitable water iodine content. Older women were less likely to have higher urinary iodine concentration (P = 0.041). Pregnant women who consumed milk > 4 times weekly during pregnancy were more likely to be iodine sufficient (P = 0.028). Living in areas with high water iodine content for > 5 years is a risk factor for iodine excess (P < 0.001, P = 0.007). There is a probability of higher urinary iodine concentration in pregnant and lactating women and their infants living in areas with high water iodine content. Age had an effect on iodine excess in lactating women. Consumption of milk > 4 times a week during pregnancy and living in an area with high iodine water content for > 5 years were associated with iodine sufficiency and iodine excess in pregnant women.

Breast Milk Iodine Concentration Is Associated with Infant Growth, Independent of Maternal Weight

In breastfed infants, human milk provides the primary source of iodine to meet demands during this vulnerable period of growth and development. Iodine is a key micronutrient that plays an essential role in hormone synthesis. Despite the importance of iodine, there is limited understanding of the maternal factors that influence milk iodine content and how milk iodine intake during infancy is related to postnatal growth. We examined breast milk samples from near 2 weeks and 2 months post-partum in a mother-infant dyad cohort of mothers with pre-pregnancy weight status defined by body mass index (BMI). Normal (NW, BMI < 25.0 kg/m2) is compared to overweight/obesity (OW/OB, BMI ≥ 25.0 kg/m2). The milk iodine concentration was determined by inductively coupled plasma mass spectrometry. We evaluated the associations between iodine content at 2 weeks and infant anthropometrics over the first year of life using multivariable linear mixed modeling. Iodine concentrations generally decreased from 2 weeks to 2 months. We observed no significant difference in iodine based on maternal weight. A higher iodine concentration at 2 weeks was associated with a larger increase in infant weight-for-age and weight-for-length Z-score change per month from 2 weeks to 1 year. This pilot study shows that early iodine intake may influence infant growth trajectory independent of maternal pre-pregnancy weight status.

A Hospital-Based Study of Iodine Nutrition Status of Breastfeeding Mothers in Bangladesh

Adequacy of iodine nutrition status in breastfeeding mothers is vital in preventing iodine deficiency disorder (IDD) in neonates and children. The aim of the study was to assess urinary iodine status in breastfeeding mothers attending Bangabandhu Sheikh Mujib Medical University (BSMMU) hospital in Bangladesh. In this cross-sectional study carried out from January 2014 to January 2015, urinary iodine (UI; μgm/L) level of 266 mothers (age 26.6 ± 4.7 years (mean ± SD), exclusively breastfeeding: 132 and nonexclusively breastfeeding: 134), recruited on consecutive basis from BSMMU outdoor and indoor, were measured in spot urine following the wet digestion method. Median UI in the participants was 298.6 (interquartile range, IQR 206.6-454.9) μgm/L and only 6.4% lactating mother had low UI (i.e. <100 μgm/L). There was no difference of median UI in relation to exclusive or nonexclusive breast feeding, presence of goiter, parity, and age of breastfed baby (p=ns for all). But median UI was higher in older subjects (≥30 years vs. <30 years: 364.4 (228.4-529.9) vs. 283.7 (205.4-434.0); median (IQR) p=0.040)), with good socioeconomic condition (good vs. average or less: 328.2 (243.8-510.0) vs. 274.4 (200.0-433.3); median (IQR); p=0.020), and in those who are aware regarding the importance of iodine (aware vs. unaware: 316.6 (225.2-506.3) vs. 270.1 (196.0-407.2); median (IQR); p=0.018). The proportion of participants with UI < 100 μgm/L was similar in all the groups. Logistic regressions to predict deficient UI status revealed none of the variables to be an independent predictor. This study indicates that deficient iodine nutrition status in Bangladeshi breastfeeding mothers is not frequent at present.

Variation of iodine concentration in breast milk and urine in exclusively breastfeeding women and their infants during the first 24 wk after childbirth

OBJECTIVE

The aim of this study was to observe the variation of iodine concentration in breast milk and urine in exclusively breastfeeding women and their infants during the first 24 wk after childbirth.

METHODS

In all, 634 exclusively breastfeeding mother-infant pairs were enrolled at hospital and followed at the 1, 4, 8, 12, 16, and 24 wk postpartum. Spot infant urinary iodine concentration (I-UIC), maternal urinary iodine concentration UIC (M-UIC), and breast milk iodine concentration (BMIC) in bilateral breasts were measured.

RESULTS

During the first 24 wk, the median I-UIC was 216 (139-362) and 122 (68-217) μg/L in lactating mothers, both indicating iodine sufficiency. A strong correlation and no difference were found between BMIC in bilateral breasts. The mean BMIC (M-BMIC) of the two breasts was 165 (112-257) μg/L with a Bland-Altman index of 2.1%. Positive correlations were found between M-BMIC and I-UIC (r = 0.353, P < 0.001), between M-BMIC and M-UIC (r = 0.339, P < 0.001), and between I-UIC and M-UIC (r = 0.222, P < 0.001). M-BMIC was significantly higher than M-UIC (P < 0.001) and lower than I-UIC (P < 0.001). M-BMIC declined from week 1 to week 8 postpartum, both I-UIC and M-UIC dropped from week 1 to week 4 postpartum and stabilized thereafter.

CONCLUSION

The iodine nutrition in lactating women and infants were adequate during the first 24 wk after childbirth. M-BMIC declined from week 1 to week 8 postpartum. Both I-UIC and M-UIC dropped from week 1 to week 4 postpartum. Further studies are needed to explore a more definitive BMIC and UIC range for an optimal iodine status in lactating women and breastfed infants.

Effects of mandatory salt iodization on breast milk, urinary iodine concentrations, and thyroid hormones: is iodine deficiency still a continuing problem?

PURPOSE

To investigate whether mandatory use of iodized salt in Turkey, since 1999 has sufficient effects on pregnant women and their newborns' urinary iodine concentrations (UIC), maternal and newborns' thyroid function tests and breast milk iodine concentrations (BMIC).

METHODS

This cross-sectional analytical-type study was conducted in an obstetrics and gynecology hospital in Konya, Turkey. One hundred and seven pregnant women and their 107 full-term newborns were included into the study. Levels of pregnant women and their newborns' UIC, thyroid-stimulated hormone (TSH), free triiodothyronine (fT3), free thyroxine (fT4), thyroglobulin (Tg), and BMIC were studied.

RESULTS

Of 107 women with term pregnancy, mean TSH value and hypothyroidism frequency were found as 2.34 ± 1.33 mIU/L and 18.7%, respectively. Cord blood TSH level was found higher (≥ 10 mIU/L) in five newborns. Accordingly, the incidence of transient congenital hypothyroidism was 4.7% (5/107). Tg levels were observed to be higher in 50.5% of newborns and 22.4% of pregnant women. Frequency of iodized salt use in pregnancies was detected as 96.3% in general population, 97.5% in urban, and 92.9% in rural areas. Of pregnancies and newborns, 57.9 and 53.3% were found to have deficient urinary iodine, respectively, and BMIC deficiency was detected as 52.0%. There was a significant positive correlation between pregnant women's UIC, and newborns' UIC and BMIC.

CONCLUSIONS

Despite the effective struggle with iodine deficiency and salt iodination control program in Konya, we concluded that iodine deficiency still persists as a significant problem in pregnancies.

High iodine content in local animal milk and risk of exceeding EFSA upper intake level for iodine among Saharawi women

Excessive iodine intake is a major public health problem in the Saharawi refugee camps in Algeria, where animal milk is an important source of iodine. The purpose of this study was to assess the association between iodine concentrations in locally produced animal milk and in animal drinking water and further to assess the risk of exceeding European Food Safety Authority (EFSA) tolerable upper intake level for iodine (600 μg/d) among Saharawi women. In 2009 and 2010, 202 milk samples from goats and sheep and 52 milk samples from camel were collected. Iodine in milk was determined by Inductively Coupled Plasma-Mass Spectrometry (ICP-MS). In addition, iodine in 56 water samples from the general water system and 54 water samples from wells, was determined by modified Sandell-Kolthoff reaction. Animal milk is generally consumed mixed with water. The median (min, max) iodine intake from goat/sheep milk mixed with water in camps with high iodine content in human drinking water was 284 (57, 2889) μg/d and 19% of participants exceeded EFSA upper intake level for iodine. The median (min, max) iodine intake from camel milk mixed with water in all camps was 2100 (210, 11100) and 47% of participants exceeded the EFSA upper intake level. The median (min, max) iodine content in goat/sheep milk from camps with moderate and high iodine content in water was 507 (101, 4791) μg/L and 1612 (487, 9323) μg/L, respectively (p < 0.001). The iodine content in goat/sheep milk was positively associated with iodine content in animal drinking water (regression coefficient, B 5.71, 95% CI 4.03, 7.39). In conclusion, consumption of camel milk and living in camps with high water iodine content increased the risk of exceeding the EFSA upper intake level for iodine. We suggest that purified water for both human and animal consumption should be provided.

A Linkage Between Thyroid and Breast Cancer: A Common Etiology?

Breast and thyroid cancers are two malignancies with highest incidence in women. These cancers often occur metachronously. Women with thyroid cancer are at increased risk for subsequent breast cancer; women with breast cancer have an increased incidence of later development of thyroid cancer, suggesting a common etiology. This bidirectional relationship is reported worldwide; however, the underlying reasons for this co-occurrence are unknown. In this review, we summarize the current epidemiologic evidence and putative mechanisms of these metachronous or synchronous cancers. Key potential causative factors are chemotherapy and radiotherapy of the primary tumor, genetic variants linking the two diseases, hormonal signaling both from the thyroid gland and from estrogens, and lifestyle and environmental factors. There is a critical need for additional epidemiologic studies focused on gender and regional incidence together with molecular investigations on common tumorigenic pathways in these endocrine cancers. Understanding the putative mechanisms will aid in the diagnosis and clinical management of both diseases.

Lactating Mothers and Infants Residing in an Area with an Effective Salt Iodization Program Have No Need for Iodine Supplements: Results from a Double-Blind, Placebo-Controlled, Randomized Controlled Trial

BACKGROUND

The necessity of iodine supplementation in lactating mothers residing in countries with sustained salt iodization programs for iodine sufficiency of breast-fed infants remains unclear. The aims of this study were to investigate the effect of iodine supplementation on iodine status and growth parameters of lactating mothers and breast-fed infants and to compare these data with that of formula-feeding mothers and their infants during the first year of infancy.

METHODS

In this multicenter, double-blinded, randomized clinical trial conducted in four healthcare centers in Tehran (Iran), healthy lactating mothers and their term newborns aged 3-5 days were randomly assigned to treatment groups: placebo, 150 μg/day iodine, or 300 μg/day iodine. They were followed up for 12 months. Formula-fed infants aged 30-45 days and their mothers were randomly selected from the same centers. The primary outcomes were maternal and infant urinary iodine concentrations (UICs), breast-milk iodine concentrations (BMICs), and infant growth parameters, measured at 1, 2, 4, 6, 9, and 12 months during routine health visits. The formula-fed group was assessed at 2, 4, 6, 9, and 12 months of age. Analysis was by per protocol principle using mixed-effects models.

RESULTS

Mother-newborn pairs (n = 180) in treatment groups and partially/exclusively formula-feeding mother-infant pairs (n = 60) participated between October 2014 and January 2016. Median baseline UICs in the treatment groups were 84 μg/L (interquartile range [IQR] 41-143 μg/L) in mothers and 208 μg/L (IQR 91-310 μg/L) in their infants. The values in the formula-fed group were 76 μg/L (IQR 40-144 μg/L) in mothers and 121 μg/L (IQR 66-243 μg/L) in infants. The 300 μg/day iodine group showed significantly higher UICs and BMICs than did the other treatment groups; infant UICs in the 150 μg/day iodine, placebo, and formula-fed groups were similar. Infants in all groups showed iodine sufficiency (median UIC ≥100 μg/L) throughout the study period. Anthropometric measurements were similar between the treatment and formula-fed groups over the study period, except at the last follow-up visit at 12 months.

CONCLUSION

Supplementation of breast-feeding mothers with either 300 or 150 μg/day iodine improved their iodine status. However, the iodine status of infants in all groups studied indicated iodine sufficiency during the first year of infancy, demonstrating that in countries with effective salt iodization program, iodine supplementation for lactating mothers is unnecessary.

High Urinary Iodine Concentration Among Breastfed Infants and the Factors Associated with Iodine Content in Breast Milk

Iodine deficiency in infants leads to delayed growth and development. Some studies have reported iodine deficiency among infants and lactating women. We assessed iodine status in infants and lactating women, as well as the iodine content in breast milk. A cross-sectional study enrolled mother-infant pairs (infants aged 4-6 months), who visited Well Child Clinic at Ramathibodi Hospital, Bangkok, Thailand. Infants were classified by feeding type as breastfed (BF), mixed breastfed and formula-fed (MF), and formula-fed (FF). Demographic and perinatal data were collected. The urinary iodine concentration (UIC) of infants and lactating women, and breast milk iodine concentration (BMIC) were analyzed. Seventy-one infants were enrolled. The median UIC of infants was 282 mcg/L. Breastfed infants had higher median UIC than formula-fed infants (553 vs. 192 mcg/L; p = 0.002). Forty-eight percent of infants had a UIC more than 300 mcg/L. The median UIC and BMIC of lactating women were 149 and 255 mcg/L, respectively. Among the BF group, the infant UIC was correlated with maternal UIC (r_s = 0.857, p = 0.014). Multiple linear regression showed the BMIC to be associated with maternal UIC (β = 4.03, 95% CI [1.34, 6.71]) and maternal weight (β = 8.26, 95%CI [2.76, 13.77]). Iodine nutrition among our study population was adequate. The median UIC of infants and lactating mothers were 282 and 149 mcg/L, respectively. Breastfed infants had a significantly higher median UIC than formula-fed infants. The BMIC was associated with maternal UIC and maternal weight.

A Nonpump Function of Sodium Iodide Symporter in Thyroid Cancer via Cross-talk with PTEN Signaling

The sodium iodide symporter (NIS) is a classical iodide pump typically localized within the cell plasma membrane in thyroid cells, where NIS expression is believed to ensure success of mainstay radioiodide therapy in thyroid cancers. Although radioiodide uptake is generally reduced in thyroid cancer tissue, intracellular nonmembranous NIS has been reported to increase, suggesting that NIS serves a pump-independent function. Thyroid cancer is one of the major component cancers of Cowden syndrome, a subset of which is caused by germline mutations in PTEN In this study, we explored the noncanonical tumorigenic role of NIS in thyroid cancer cells in relation to PTEN signaling. PTEN knockdown in thyroid cancer cell lines stabilized intracellular NIS protein by promoting an interaction with NIS-LARG (leukemia-associated RhoA guanine exchange factor). Increased protein levels of cytoplasmic NIS enhanced RhoA activation and resulted in a promigration tumorigenic phenotype. Inhibition of NIS glycosylation through activation of the PI3K/AKT/mTOR signaling pathway contributed to mislocalization of NIS in the cytoplasm, facilitating its nonpump tumorigenic function through an interaction with LARG, which predominantly localized in the cytoplasm. Moreover, PTEN or PI3K/AKT/mTOR signaling could affect DPAGT1, a glycosylating enzyme involved in the initial step of N-linked glycosylation, to inhibit glycosylation of NIS. In summary, our results elucidate a pump-independent, protumorigenic role for NIS in thyroid cancer via its cross-talk with PTEN signaling.Significance: A novel pump-independent protumorigenic role of nonmembranous NIS challenges the presumption that radioiodine treatment of thyroid cancer is ineffective when transmembrane NIS is not expressed. Cancer Res; 78(21); 6121-33. ©2018 AACR.

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.

Limitations of the Evidence Base Used to Set Recommended Nutrient Intakes for Infants and Lactating Women

Reported values for concentrations of micronutrients in human milk form the basis of the majority of micronutrient intake recommendations for infants and the additional maternal requirements for lactation. The infant recommendations may also be extrapolated to provide estimates for young children. The purpose of this review is to evaluate the adequacy of the milk micronutrient concentration data used by the Institute of Medicine to set recommendations for the United States and Canada, by FAO/WHO, the United Kingdom, and the European Food Safety Authority. The concentrations accepted by each agency are presented for each micronutrient accompanied by the source of information and comments on the number, location, status, and stage of lactation of the sample population, where known. These summaries show the small number of participants from which samples were collected in most studies, the wide range of concentrations within studies, the lack of longitudinal data, and the variability in collection methods. These factors contribute to the variability in nutrient intake recommendations among committees, although this variability is reduced by some committees that accept milk-composition values proposed by others. Values are also summarized from milk collected in studies in which mothers or infants were known to be deficient on the basis of clinical symptoms, biomarkers of inadequacy, or both, to show the extent to which milk micronutrients can be reduced by poor maternal nutritional status. We conclude that a new, multicenter study is needed to establish reference values for milk constituents across lactation.

Overview of Nutrients in Human Milk

The WHO recommends exclusive breastfeeding for the first 6 mo of life to promote optimal infant health and development. Understanding the micro- and macronutrient concentrations of human milk and how each nutrient fluctuates with lactational stage, maternal factors, and supplementation is imperative for supporting good breastfeeding practices. Where maternal undernutrition compromises human milk quality, a thorough awareness of the effectiveness of interventions can direct efforts to achieve both maternal and infant nutrient sufficiency. This review of current knowledge covers trends in nutrient concentrations over the course of lactation and describes the influence of maternal intake, status, supplementation, and other factors on human milk concentrations of each nutrient.

Is there any difference between the iodine statuses of breast-fed and formula-fed infants and their mothers in an area with iodine sufficiency?

Despite substantial progress in the global elimination of iodine deficiency, lactating mothers and their infants remain susceptible to insufficient iodine intake. This cross-sectional study was conducted to compare iodine statuses of breast-fed and formula-fed infants and their mothers at four randomly selected health care centres in Tehran. Healthy infants <3 months old and their mothers were randomly selected for inclusion in this study. Iodine was measured in urine and breast milk samples from each infant and mother as well as commercially available infant formula. The study included 124 postpartum mothers (29·2 (sd 4·9) years old) and their infants (2·0 (sd 0·23) months old). The iodine concentrations were 50–184 µg/l for infant formula, compared with a median breast milk iodine concentration (BMIC) of 100 µg/l in the exclusive breast-feeding group and 122 µg/l in the partial formula feeding group. The median values for urinary iodine concentration in the exclusive breast-feeding group were 183 µg/l (interquartile range (IQR) 76–285) for infants and 78 µg/l (IQR 42–145) for mothers, compared with 140 µg/l (IQR 68–290) for infants and 87 µg/l (IQR 44–159) for mothers in the formula feeding group. These differences were not statistically significant. After adjustment for BMIC, ANCOVA revealed that feeding type (exclusive breast-feeding v. partial formula feeding) did not significantly affect the infants’ or mother’s urinary iodine levels. Thus, in an area with iodine sufficiency, there was no difference in the iodine statuses of infants and mothers according to their feeding type.

Interrelationship between iodine nutritional status of lactating mothers and their absolutely breast-fed infants in coastal districts of Gangetic West Bengal in India

Iodine nutritional status of 128 lactating mothers and their breast-fed infants (1-3 months) from iodine-replete villages during post-salt iodization period was evaluated. Mothers' urine, blood, and breast milk (BM) and infants' urine and blood were collected and analyzed for iodine and serum FT₄ and TSH estimation. Mothers' and infants' age, parity, occupation, education, and household income were recorded. Median urinary iodine concentration (UIC) of infants was 250 μg/L, indicating their iodine intake was more than adequate. Mothers' median UIC was 185 μg/L, indicating adequate iodine nutrition; however, 13.28% had mild to severe deficiency. Median breast milk iodine concentration (BMIC) was 230 μg/L, which was more than their median UIC 185 μg/L. In iodine-deficient mothers, positive correlation was found between mothers' and infants' serum FT₄ and TSH levels, and negative correlation was found between mothers' and infants' serum FT₄ and TSH levels in excessive iodine nutrition group.

CONCLUSION

Iodine intake of breast-fed infants was at the limit of above requirement, and they are possibly at the risk of excess iodine intake. In iodine deficient and excessive iodine intake mothers, their infants' serum FT₄ and TSH are independent on their iodine nutritional status but dependent on thyroid hormone profile of their mothers but differently. What is Known: • A median urinary iodine of 100 μg/L is used to define adequate iodine intake of lactating mothers and children < 2 years. However, adequate iodine intake in terms of urinary iodine of infants of age 1-3 months is not known. What is New: • Iodine intake of absolutely breast-fed infants (1-3 months) was more than adequate, though their mother's intake was adequate as breast milk contains more iodine than urine. The infants of iodine deficient and excessive iodine intake mothers, infants' hormonal profile is independent of their iodine nutritional status but dependent on their mothers thyroid hormone profile.

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.

Iodine status of postpartum women and their infants in Australia after the introduction of mandatory iodine fortification

Mandatory I fortification in bread was introduced in Australia in 2009 in response to the re-emergence of biochemical I deficiency based on median urinary I concentration (UIC)<100 µg/l. Data on the I status of lactating mothers and their infants in Australia are scarce. The primary aim of this study was to assess the I status, determined by UIC and breast milk I concentration (BMIC), of breast-feeding mothers in South Australia and UIC of their infants. The secondary aim was to assess the relationship between the I status of mothers and their infants. The median UIC of the mothers (n 686) was 125 (interquartile range (IQR) 76-200) µg/l and median BMIC (n 538) was 127 (IQR 84-184) µg/l. In all, 38 and 36 % of the mothers had a UIC and BMIC below 100 µg/l, respectively. The median UIC of infants (n 628) was 198 (IQR 121-296) µg/l, and 17 % had UIC<100 µg/l. Infant UIC was positively associated with maternal UIC (β 0·26; 95 % CI 0·14, 0·37, P<0·001) and BMIC (β 0·85; 95 % CI 0·66, 1·04, P<0·001) at 3 months postpartum after adjustment for gestational age, parity, maternal secondary and further education, BMI category and infant feeding mode. The adjusted OR for infant UIC<100 µg/l was 6·49 (95 % CI 3·80, 11·08, P<0·001) in mothers with BMIC<100 µg/l compared with those with BMIC≥100 µg/l. The I status of mothers and breast-fed infants in South Australia, following mandatory I fortification, is indicative of I sufficiency. BMIC<100 µg/l increased the risk of biochemical I deficiency in breast-fed infants.

Comparison of two sources of iodine delivery on breast milk iodine and maternal and infant urinary iodine concentrations in southern Ethiopia: A randomized trial

Iodine deficiency during pregnancy and lactation could expose the infant to severe iodine deficiency disorders. A randomized supplementation trial among rural lactating women was conducted in Sidama zone, southern Ethiopia, to compare the methods of iodine delivery on breast milk iodine, and on maternal and infant urinary iodine concentrations. Women were randomly assigned either to receive 225 μg iodine as potassium iodide capsule daily for 6 months or 450 g of appropriately iodized salt (30-40 μg I as KIO3/g of salt) weekly for household consumption for 6 months. Breast milk iodine concentration (BMIC) and maternal and infant urinary iodine concentration (UIC) were measured at baseline and at 6 months. The women did not differ in BMIC and UIC, and infants did not differ in UIC in a time by treatment interaction. Median (IQR, interquartile range, IQR) BMIC at baseline was 154 [43, 252] μg/L and at 6 months was 105 [36, 198] μg/L, maternal UIC at baseline was 107 [71, 161] μg/L and at 6 months was 130 [80, 208] μg/L; infant UIC at baseline was 218 [108, 356] μg/L and at 6 months was 222 [117, 369] μg/L. Significant correlations among the three variables were obtained in both groups at both times. We conclude that for lactating women an adequate amount of appropriately iodized salt (30-40 μg I/g) had similar effects as a daily supplement of 225 μg I on BMIC and on maternal and infant UIC.