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.

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The impact of iodised salt or iodine supplements on iodine status during pregnancy, lactation and infancy

Public Health Nutrition ◽

10.1017/s1368980007360965 ◽

2007 ◽

Vol 10 (12A) ◽

pp. 1584-1595 ◽

Cited By ~ 50

Author(s):

Michael B Zimmermann

Keyword(s):

Pregnant Women ◽

Urinary Iodine ◽

Iodine Concentration ◽

Iodine Intake ◽

Urinary Iodine Concentration ◽

Life Stages ◽

Lactating Women ◽

Iodine Status ◽

Iodised Salt ◽

The Impact

AbstractObjectives:Monitoring of iodine status during pregnancy, lactation and infancy is difficult as there are no established reference criteria for urinary iodine concentration (UI) for these groups; so it is uncertain whether iodized salt programs meet the needs of these life stages.Design and Subjects:The method used in this paper was: 1) to estimate the median UI concentration that reflects adequate iodine intake during these life stages; and 2) to use these estimates in a review of the literature to assess whether salt iodisation can control iodine deficiency in pregnant and lactating women, and their infants.Results:For pregnancy, recommended mean daily iodine intakes of 220-250 μg were estimated to correspond to a median UI concentration of about 150 μg l− 1, and larger surveys from the iodine sufficient countries have reported a median UI in pregnant women ≥ 140 μg l− 1. Iodine supplementation in pregnant women who are mild-to-moderately iodine deficient is beneficial, but there is no clear affect on maternal or newborn thyroid hormone levels. In countries where the iodine intake is sufficient, most mothers have median breast milk iodine concentration (BMIC) greater than the concentration (100-120 μg l− 1) required to meet an infant's needs. The median UI concentration during infancy that indicates optimal iodine nutrition is estimated to be ≥ 100 μg l− 1. In iodine-sufficient countries, the median UI concentration in infants ranges from 90-170 μg l− 1, suggesting adequate iodine intake in infancy.Conclusions:These findings suggest pregnant and lactating women and their infants in countries with successful sustained iodised salt programs have adequate iodine status.

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Iodine nutrition in pregnancy and lactation in Iran

Public Health Nutrition ◽

10.1017/s1368980007360977 ◽

2007 ◽

Vol 10 (12A) ◽

pp. 1596-1599 ◽

Cited By ~ 22

Author(s):

Fereidoun Azizi

Keyword(s):

Pregnant Women ◽

Urinary Iodine ◽

Thyroid Volume ◽

Iodine Concentration ◽

Iodine Intake ◽

Urinary Iodine Excretion ◽

Urinary Iodine Concentration ◽

Lactating Women ◽

Iodine Excretion ◽

Pregnancy And Lactation

AbstractObjective: To describe studies evaluating urinary iodine excretion during pregnancy and lactation in women living in cities with adequate or more than adequate iodine intake.Design: Cross-sectional study conducted between 1996 and 1998 in pregnant women and a study of lactating women conducted in 2003.Settings and Subjects: Pregnant women attending prenatal clinics in four cities in the Islamic Republic of Iran. Urinary iodine excretion and thyroid volume was measured in 403 women. In a second study, 100 lactating women from Taleghani Hospital in Gorgan, Iran were evaluated for thyroid size, and both urinary and breast milk iodine concentrations were determined.Results: In Rasht city, 84% of pregnant women had a urinary iodine concentration of ≥ 200 μg l-1, while in the other cities this percentage ranged from 45 to 55%. When data were combined for the cities of Ilam, Isfahan and Tehran, where women have an adequate or more than adequate median urinary iodine concentration, 51% of pregnant women had a urinary iodine concentration less than that recommended during pregnancy. In Rasht, where the median urinary iodine concentration indicates an excessive iodine intake, 15.4% of pregnant women had a urinary iodine concentration < 200 μg l-1. The mean urinary iodine concentration in lactating women was 250 μg l-1, and 16% of women had a urinary iodine concentration < 100 μg l-1. Grade 1 goitre was present in 8% of lactating women, and another 8% had grade 2 goitre.Conclusions: Findings of this study call for further attention to iodine intake during pregnancy and lactation. The currently recommended intake of iodine through universal salt iodisation may not be adequate for pregnant and lactating women, and supplementation during pregnancy and lactation should be further considered in light of the latest recommendations.

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Iodine nutrition of pregnant and lactating women in Hong Kong, where intake is of borderline sufficiency

Public Health Nutrition ◽

10.1017/s1368980007360989 ◽

2007 ◽

Vol 10 (12A) ◽

pp. 1600-1601 ◽

Cited By ~ 9

Author(s):

Annie WC Kung

Keyword(s):

Hong Kong ◽

Breast Milk ◽

Urinary Iodine ◽

Iodine Concentration ◽

Iodine Intake ◽

Normal Serum ◽

Urinary Iodine Concentration ◽

Iodine Nutrition ◽

Cross Sectional ◽

Lactating Women

AbstractObjective: To describe the iodine nutrition of pregnant and lactating women in Hong Kong, where intake is of borderline sufficiency.Design: Review of cross-sectional and prospective studies.Setting: China, Hong Kong Special Administrative Region (SAR).Subjects: Pregnant and lactating women.Results: Studies of pregnant women in Hong Kong SAR have revealed an increase in the urinary iodine (UI) concentration as pregnancy advances. A significant percentage of women had a sub-normal serum thyroid hormone concentration at full term. Although iodine is concentrated by the mammary gland, 19% of all mothers had low iodine concentrations in their breast milk. The moderate correlation between the concentrations of iodine in breast milk and urine suggests that an adequate maternal urinary iodine concentration cannot reliably indicate that an infant is getting enough iodine in breast milk. Therefore, some breast-fed infants may still be at risk of low iodine intake, and additional iodine supplements, other than salt iodisation, would be warranted in this population.Conclusions: The currently recommended intake of iodine through universal salt iodisation may not be adequate for pregnant and lactating women, and supplementation during pregnancy and lactation should be further considered in light of the latest recommendations.

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High Iodine Deficiency among Pregnant Women in Periurban Ghana: A Hospital-Based Longitudinal Study

Journal of Nutrition and Metabolism ◽

10.1155/2018/9706805 ◽

2018 ◽

Vol 2018 ◽

pp. 1-5

Author(s):

David Larbi Simpong ◽

Yaw Asante Awuku ◽

Kenneth Kwame Kye-Amoah ◽

Martin Tangnaa Morna ◽

Prince Adoba ◽

...

Keyword(s):

Longitudinal Study ◽

Pregnant Women ◽

Iodine Deficiency ◽

Urinary Iodine ◽

Clinical Information ◽

Iodine Concentration ◽

Iodized Salt ◽

Urinary Iodine Concentration ◽

Study Cohort ◽

Iodine Sufficiency

Background. Iodine deficiency causes maternal hypothyroidism which can lead to growth, cognitive, and psychomotor deficit in neonates, infants, and children. This study examined the iodine status of pregnant women in a periurban setting in Ghana. Methods. This longitudinal study recruited 125 pregnant women by purposeful convenience sampling from the antenatal clinic of the Sefwi Wiawso municipal hospital in Ghana. Urinary iodine concentration (UIC) was estimated by the ammonium persulfate method at an estimated gestational age (EGA) of 11, 20, and 32 weeks. Demographic information, iodized salt usage, and other clinical information were collected using a questionnaire. Results. The prevalence of iodine deficiency among the pregnant women was 47.2% at EGA 11 and 60.8% at both EGA of 20 and 32, whereas only 0.8% of participants not using iodized salt had iodine sufficiency at EGA 32. 18.4%, 20%, and 24% of participants using iodized salt had iodine sufficiency at EGA 11, 20, and 32, respectively. Conclusion. A high prevalence of iodine deficiency was observed among our study cohort.

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Urinary iodine concentration: a biochemical parameter for assessing the iodine status

Mediscope ◽

10.3329/mediscope.v5i2.37146 ◽

2018 ◽

Vol 5 (2) ◽

pp. 30-35

Author(s):

GM Molla

Keyword(s):

Iodine Deficiency ◽

Urinary Iodine ◽

Iodine Concentration ◽

Iodine Intake ◽

Urinary Iodine Concentration ◽

Lactating Women ◽

Iodine Status ◽

Excessive Iodine ◽

Pregnancy And Lactation ◽

Neonates And Infants

Iodine is a micronutrient, which is essential for the synthesis of thyroid hormones. Thyroid hormones play a major role in the development of different functional components in different stages of life. The relationship between iodine intake level of a population and occurrences of thyroid disorders U-shaped with an increase from both low and high iodine intake. Iodine deficiency disorders (IDDs) are a major health problem worldwide in all age groups, but infants, school children, and pregnant and lactating women are vulnerable. During pregnancy and lactation, the fetus and infants are sensitive to maternal iodine intake. Even mild iodine deficiency may lead to irreversible brain damage during this period. A main cause of IDDs of neonates and infants is maternal iodine deficiency. Universal salt iodization strategy has been initiated by the World Health Organization and United Nation International Children Emergency Fund by the year 1993 for correction and prevention of iodine deficiency. Excessive iodine causes hypothyroidism, iodine-induced hyperthyroidism and autoimmune thyroid diseases. Iodine deficiency and excessive iodine, both cause goiter. There are many indicators for assessing the IDDs, such as measurement of thyroid size by palpation or ultrasonography, serum thyroid stimulating hormone, and thyroglobulin but these are less sensitive, costly and sometimes interpretation is difficult. Urinary iodine concentration (UIC) is a well-accepted, cost-efficient, and easily obtainable indicator of iodine status. Since the majority of iodine absorbed by the body is excreted in the urine, it is considered a sensitive marker of current iodine intake and can reflect recent changes in iodine status. Iodine requirements are greatly increased during pregnancy and lactation, owing to metabolic changes. During intrauterine life, maternal iodine is the only source of iodine for a fetus. UIC determines the iodine status of pregnant and lactating women. Breast milk is the only source of iodine for exclusively breastfed neonates and infants. Breast milk iodine concentration can be determined by UIC. UIC predicts the adverse health consequences of excessive iodine intake such as goiter, hypothyroidism, and hyperthyroidism. This review presents that iodine status in different groups of a population can be determined by UIC which will be helpful in assessing the iodine status in a community, finding out the cause of thyroid disorders, to predict the risk of adverse health effects of iodine deficiency and excessive iodine, and in making plan for iodine supplementation.Mediscope Vol. 5, No. 2: Jul 2018, Page 30-35

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Hypothyroidism among females and differences in their dietary patterns and urinary iodine concentrations compared to normal subjects

Asian Journal of Dairy and Food Research ◽

10.18805/ajdfr.v36i03.8969 ◽

2017 ◽

Vol 36 (03) ◽

Author(s):

Nidhi Budhalakoti ◽

Kalpana Kulshrestha

Keyword(s):

Dietary Habits ◽

Dietary Diversity ◽

Urinary Iodine ◽

Food Preferences ◽

Normal Subjects ◽

Iodine Concentration ◽

Urinary Iodine Concentration ◽

Endocrine Disorders ◽

Dietary Intakes ◽

Significant Difference

Thyroid disorders are among the most common endocrine disorders in India. Hypothyroidism is a very common condition. The condition is more common in women than in men, and its incidence increases with age. For the present study 150 females of 21 to 50 years of age were selected via random sampling from Pantnagar area of Udham Singh Nagar District, Uttarakhand and were interviewed using a predesigned proforma. The subjects mainly belonged to middle and upper income groups. Among 150 subjects, 30 were found to be suffering from hypothyroidism of which six were the newly diagnosed cases who had not started medications. Subjects were assessed for their dietary intakes and differences in the food habits based on food avoidance, food preferences, dietary habits and dietary diversity scores. Based on the analysis of the dietary intakes of normal (n=120) and hypothyroid (n=30) subjects not much difference was found, as was also evident from the dietary diversity scores (where non-significant difference was observed) except for in case of some dietary habits which showed significant differences. The mean dietary diversity scores of hypothyroid and normal subjects were 5.8±0.88 and 6.0±0.90 respectively. Urine samples were also collected for the measurement of urinary iodine concentration of only 30 subjects which included six of the newly detected hypothyroid cases not on medication and the remaining 24 normal subjects. Only 2 hypothyroid subjects and 3 normal subjects were found to be suffering from mild iodine deficiency with values of urinary iodine ranging from 76.5 to 94.6µg/l. Median urine iodine excretion in the present study was 172 µg/l (mean 186.5±58.4 µg/l) indicating iodine sufficiency.

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Development and validation of an iodine-specific FFQ to estimate iodine intake in Australian pregnant women

British Journal Of Nutrition ◽

10.1017/s0007114515000197 ◽

2015 ◽

Vol 113 (6) ◽

pp. 944-952 ◽

Cited By ~ 14

Author(s):

Dominique Condo ◽

Maria Makrides ◽

Sheila Skeaff ◽

Shao J. Zhou

Keyword(s):

Pregnant Women ◽

Urinary Iodine ◽

Optimal Growth ◽

Iodine Concentration ◽

Iodine Intake ◽

Urinary Iodine Excretion ◽

Urinary Iodine Concentration ◽

Food Record ◽

Total Iodine ◽

Supplement Use

Adequate iodine is important during pregnancy to ensure optimal growth and development of the offspring. We validated an iodine-specific FFQ (I-FFQ) for use in Australian pregnant women. A forty-four-item I-FFQ was developed to assess iodine intake from food and was administered to 122 pregnant women at 28 weeks gestation. Iodine supplement use was captured separately at 28 weeks gestation. Correlation between iodine intake from food estimated using the I-FFQ and a 4 d weighed food record as well as correlation between total iodine intake and 24 h urinary iodine excretion (UIE), 24 h urinary iodine concentration (UIC), spot UIC and thyroid function were assessed at 28 weeks gestation. A moderate correlation between the two dietary methods was shown (r0·349,P< 0·001), and it was strengthened with the addition of iodine supplements (r0·876,P< 0·001). There was a fair agreement (k= 0·28,P< 0·001) between the two dietary measures in the classification of women as receiving adequate ( ≥ 160 μg/d) or inadequate ( < 160 μg/d) iodine intake from food, but the limits of agreement from the Bland–Altman plot were large. Total iodine intake was associated with 24 h UIE (β = 0·488,P< 0·001) but not with spot UIC. Iodine intake from food using the I-FFQ was assessed at study entry ( < 20 weeks gestation) in addition to 28 weeks gestation, and there was a strong correlation in iodine intake at the two time points (r0·622,P< 0·001), which indicated good reproducibility. In conclusion, the I-FFQ provides a valid tool for estimating iodine intake in pregnant women and can be used to screen women who are at risk of inadequate intake.

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