Journal of Thyroid Research
Volume 2019 (2019), Article ID 9896159, 5 pages
https://doi.org/10.1155/2019/9896159

Research Article

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

Jobaida Naznin,¹ Mohammad Fariduddin,¹ Mashfiqul Hasan,¹ Mohammad Atiqur-Rahman,¹ Nusrat Sultana,¹ Mohammad Anowar-Hossain,¹ Sharmin Chowdhury,² and Muhammad Abul Hasanat¹

¹Department of Endocrinology, Bangabandhu Sheikh Mujib Medical University (BSMMU), Dhaka, Bangladesh
²National Institute of Neurosciences and Hospital (NINS & H), Dhaka, Bangladesh

Correspondence should be addressed to Muhammad Abul Hasanat; hasanatdr@yahoo.com

Received 20 May 2019; Revised 5 September 2019; Accepted 13 September 2019; Published 7 October 2019

Academic Editor: Brendan C. Stack Jr.

Copyright © 2019 Jobaida Naznin et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract.

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 (). 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) )), with good socioeconomic condition (good vs. average or less: 328.2 (243.8–510.0) vs. 274.4 (200.0–433.3); median (IQR); ), 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); ). 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.

1. Introduction

Breastfeeding plays an important role in the maintenance of iodine nutrition status of breastfed babies. Neonates and infants are target population of major concern for iodine deficiency disorder. They are particularly sensitive to iodine deficiency because of the low iodine content of their thyroid glands and an extremely fast turnover of intrathyroidal iodine. Hence, the iodine nutrition status of the breastfeeding mother is a concern [1]. To date, limited attention has been paid to their iodine status despite its importance in the intellectual development of young infants especially up to the second year of life [2–4]. Iodine deficiency is the single most important preventable cause of brain damage on a worldwide basis [5]. Children living in areas affected by severe iodine deficiency may have an intelligence quotient (IQ) of up to 13.5 points below that of comparable communities in areas where there is no iodine deficiency [6]. Bangladesh has enacted national legislation mandating compulsory salt iodization since 1989 which has practically been activated since 1993. Since then, iodine deficiency (urinary iodine excretion <100 μgm/L) has been reversed to a remarkable extent [7]. But it has been emphasized by worldwide surveys that iodine deficiency disorder (IDD) can return at any time even after elimination if program success is not sustained. Also IDD can and does occur in unlikely areas like large cities and coastal areas. So, the need for continued vigilance is underlined [5].

In lactating period, iodine is concentrated in the mammary gland for more excretion in breast milk than through urine. Because of the need to ensure that the infant gets enough iodine from breast milk to build reserves in the thyroid gland, it was recommended that lactating women should continue to consume 250 micrograms of iodine per day same as during pregnancy [5, 8].

Iodine status is the most immediate measure of whether the thyroid gland has adequate iodine to function normally and protect the individual from the manifestations of iodine deficiency. Assessment of thyroid size, measurement of urinary iodine, thyroid stimulating hormone (TSH), and thyroglobulin are methods of assessing IDD prevalence. Since most countries have now started implementing IDD control programs, a WHO/UNICEF/ ICCIDD joint committee has emphasized urinary iodine as the principal indicator of impact. This indicator is highly accepted, and casual urine specimens are easy to obtain.

Most of the iodine (more than 90%) absorbed by the body is eventually excreted in the urine. The concentration of iodine in urine is an excellent indicator of recent iodine intake. Urinary iodine can vary somewhat from day to day and even within a given day in individuals. However, studies have convincingly demonstrated that a profile of iodine concentration in morning or other casual urine specimens provide an adequate assessment of a population when a sufficient number of specimens are collected [9, 10]. As urinary iodine values from populations are usually not normally distributed, the median rather than the mean should be used as the measure of central tendency.

For lactating women and children <2 years of age, a median urinary iodine concentration of 100 μg/l can be used to define adequate iodine intake, but no other categories of iodine intake are defined [5]. Optimum iodine nutrition in lactating women and their iodine requirements have been mostly calculated depending on the mean breast milk excretion and mean breast milk iodine concentration (BMIC). It is also considered to be a good biomarker of the iodine nutrition status of breastfed neonates [11]. But there is no consensus on what an adequate BMIC is, and WHO has not made a recommendation on this issue [12]. So, we assessed the urinary iodine of breastfeeding mothers attending Bangabandhu Sheikh Mujib Medical University (BSMMU) hospital in Bangladesh to find out their iodine nutrition status.

2. Materials and Methods

2.1. Study Design

This cross-sectional study encompassed 270 breastfeeding healthy mothers from January 2014 to January 2015 by purposive nonprobability sampling. Mothers were attendants of patients in outdoor and indoor of BSMMU, Dhaka, Bangladesh. Those having known thyroid disorders, chronic diseases or history of taking any iodine-containing drug were excluded.

2.2. Study Procedure

Each recruited mother was interviewed and examined by the investigators. Socioeconomic condition was judged by gross monthly income of the family. Awareness regarding iodine was assessed simply by asking whether the participants know anything regarding the need for iodine. Five milliliters of spot urine sample was collected from each subject in screw capped deiodinized plastic cups and was transferred to two tightly sealed deiodinized Eppendorfs. These were preserved under −20°C in a refrigerator to avoid unpleasant odor. One Eppendorf from each sample was kept in reserve for replicate testing and for external quality control. During processing for assay in the laboratory, 4 (four) urine samples were accidentally dropped and thus these subjects were excluded from the test. Therefore, the final number of subjects was 266.

2.3. Ethical Aspects

Written informed consent was taken from all patients after completely explaining procedure, purpose, risk, and utility of the study. Approval of the institutional review board was taken for the study.

2.4. Analytic Methods

Samples were defrosted completely before analysis. Meticulous attention was given to avoid contamination with iodine at all stages. UI was estimated using the wet digestion method of Dunn et al. with modification of Sandell and Kolthoff involving colorimetric estimation of the rate of discolouration of ceric ammonium sulphate as an inverse measure of the organic iodine present. Iodine status (as deficient or sufficient) was considered on the basis of urinary iodine cutoff at 100 μgm/l, as recommended by WHO as well as ICCIDD [5, 13, 14].

2.5. Statistical Analysis

Data from the study were analyzed using IBM SPSS Statistics for Windows version 22.0 (IBM corp, Armonk, NY, USA). Results are presented as mean (±SD) or median (interquartile range, IQR) and frequencies with percentage as applicable. Median UI of different groups was compared by Mann–Whitney U test and proportion of low UI by Chi-square or Fisher’s exact test. Iodine status was dichotomized as adequate and deficient using cutoff value to see the independent influence of other factors such as age, parity, socioeconomic status, lactation type, presence of goiter, awareness of iodine, and age of breastfed baby by multiple logistic regressions analysis. was considered statistically significant.

3. Results

The present study included 266 breastfeeding mothers irrespective of the age of their child (ranging from 0 to 24 months) in a consecutive manner of which 132 were breastfeeding exclusively and the rest nonexclusively. Mean age of the participants was 26.6 ± 4.7 years. Most of the mothers were housewives (72.2%) followed by service holders (20.3%), students (4.9%), and others (2.6%). Majority of them were residing in Dhaka (68.8%), and socioeconomically, near half of them were of average socioeconomic condition. Educational status was secondary, higher secondary, and graduate levels in around 20% of mothers, while primary level education was around 30% and masters level about 12%. Near cent percent mothers (98.5%) were taking packet salt, and more than 60% mothers were aware of the need for taking iodized salt. Around 6% mothers had a family history of thyroid disease. Most of the subjects did not show any thyroid enlargement. However, grade 1 and grade 2 goiter were present in 12.4% and 2.4%, respectively (Table 1).

Table 1: Characteristics of the studied subjects.

Variables
Frequency (%)

No. of subjects
266

Age (mean ± SD, yr)
26.6 ± 4.7

Age range (yr)
18–38

Exclusively breast feeding
132 (49.6)

Occupation

    Housewife
192 (72.2)

    Service
54 (20.3)

    Student
13 (4.9)

    Others
7 (2.6)

Area of residence

    Inside Dhaka
183 (68.8)

    Outside
83 (31.2)

Socioeconomic condition

    Poor
40 (15.0)

    Average
122 (45.9)

    Good
104 (39.1)

Educational status

    Primary
81 (30.5)

    SSC
43 (16.2)

    HSC
55 (20.7)

    Graduate
56 (21.1)

    Masters
31 (11.7)

Parity

    Unipara
130 (48.9)

    Multipara
136 (51.1)

Type of salt intake

    Open
4 (1.5)

    Packet
262 (98.5)

Aware about iodine
166 (62.4)

Positive family history of thyroid disease
17 (6.4)

Presence of goiter

    Grade 1
33 (12.4)

    Grade 2
6 (2.3)

(Within parentheses are percentages over column total).

Median UI in the participants was 298.6 (IQR 206.6–454.9) μgm/L, and only 6.4% lactating mother had low UI, that is < 100 μgm/L. When median UI of different groups were compared, it was observed that there is no difference in relation to exclusive or nonexclusive breastfeeding, presence of goiter, parity, and age of breastfed baby. 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) )), with good socioeconomic condition (good vs. average or less: 328.2 (243.8–510.0) vs. 274.4 (200.0–433.3); median (IQR); ), 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); ). The proportion of participants with deficient iodine nutrition status as evidenced by low UI < 100 μgm/L was similar in all the groups (Table 2). Multiple logistic regressions to predict deficient urinary iodine status revealed none of the variables to be an independent predictor (Table 3).

Table 2: Urinary iodine of studied mothers.

Groups of mothers
Median UI with IQR in μgm/L

UI < 100 μgm/L
UI ≥ 100 μgm/L

All subjects (n = 266)
298.6 (206.6–454.9)
—
17 (6.4)
249 (93.6)
—

Age group

    <30 years (n = 185)
283.7 (205.4–434.0)
0.040
10 (5.4)
175 (94.6)
0.321

    ≥30 years (n = 81)
364.4 (228.4–529.9)

7 (8.6)
74 (91.4)

Socioeconomic condition

    Average or less (n = 162)
274.4 (200.0–433.3)
0.020
12 (7.4)
150 (92.6)
0.398

    Good (n = 104)
328.2 (243.8–510.0)

5 (4.8)
99 (95.2)

Breast feeding status

    Exclusively (n = 132)
284.6 (196.0–441.5)
0.262
6 (4.5)
126 (95.5)
0.222

    Nonexclusively (n = 134)
316.6 (226.2–479.9)

11 (8.2)
123 (91.8)

Presence of goiter

    Goitrous (n = 39)
302.0 (205.5–448.5)
0.925
4 (10.7)
35 (89.7)
0.288

    Nongoitrous (n = 227)
297.4 (206.5–445.8)

13 (5.7)
214 (94.3)

Awareness about iodine

    Aware (n = 166)
316.6 (225.2–506.3)
0.018
8 (4.8)
158 (95.2)
0.177

    Unaware (n = 100)
270.1 (196.0–407.2)

9 (9.0)
91 (91.0)

Parity

    Unipara (n = 130)
285.8 (210.7–436.8)
0.271
5 (3.8)
125 (96.2)
0.097

    Multipara (n = 136)
319.7 (205.5–503.6)

12 (8.8)
124 (91.2)

Age of breast fed baby

    ≤6 months (n = 138)
290.8 (197.2–290.8)
0.370
7 (5.1)
131 (94.9)
0.361

    >6 months (n = 128)
310.3 (226.1–473.2)

10 (7.8)
118 (92.2)

by Mann–Whitney U test by χ2 test/Fisher’s exact test. Within parentheses are percentages over row total if not mentioned otherwise. UI: urinary iodine; IQR: interquartile range.

Table 3: Multiple logistic regressions for predictors of low urinary iodine (<100 μgm/L).

Variables

OR
95% CI for OR

Age of the mother ≥30 years
0.249
4.18
0.37–47.45

Socioeconomic status average or less
0.527
1.46
0.45–4.70

Nonexclusive breast feeding
0.173
2.21
0.71–6.88

Multiparity
0.183
2.32
0.67–7.99

Goiter
0.219
1.97
0.67–5.76

Unawareness of iodine
0.496
2.30
0.21–25.27

Age of breastfed baby ≤6 months
0.284
1.85
0.60–5.66

OR: odds ratio, CI: confidence interval.

4. Discussion

The present study aimed at assessing iodine nutrition status in breastfeeding mothers in a backdrop of established universal salt iodization program in the country. Holding the cutoff for deficiency at UI 100 μgm/L, this study clearly observed that about 94% mothers of the 266 studied subjects were sufficient with iodine nutrition status without any significant difference in proportion of sufficiency between different groups on the basis of age, socioeconomic condition, breastfeeding status, presence of goiter, awareness about iodine, parity, and age of breastfed baby. None of the variables could independently predict the deficient iodine nutrition status. However, median UI was higher in subjects with good socioeconomic condition, age >30 years and awareness regarding iodine. This findings are in agreement with some pilot studies in this country with exclusive breastfeeding mothers [15], while others in abroad observed varying results in the lactating mothers irrespective of exclusiveness of feeding; some found deficiency of UI [16, 17] and others found sufficiency [18–21].

Iodine nutrition status as assessed by median UI did not differ significantly between the exclusive and nonexclusive breastfeeding mothers in the present study. Moreover, the observed values in the present study were far higher than cutoff figure for the deficient state. It was interesting to observe that median level of UI was higher in the good socioeconomic group than in those with socioeconomic status average or less, in group aware of salt iodization than in those of the unaware group, and in the older age group (≥30 years) than in those of younger age group (<30 years). It seemed that awareness for iodized salt intake is important to improve UI. Effects of age and socioeconomic status of the mother on UI is also in concordance with other authors [22]. Median values in all groups from different views showed the level of UI far higher than the cutoff for the state of iodine deficiency. Therefore, it can be explained that the universal iodization program is working well and hopefully been adopted by the people of the country. National survey in 2004-5 showed that the prevalence of iodine deficiency was 38.6% in women [7]. Breastfeeding mothers were not an individualized subgroup despite being a vulnerable group. Nevertheless, there is concern of iodine excess in the children of these breastfeeding mothers [23]. In this context, it could be mentioned that in 2004 Hasanat et al. observed the frequency of iodine deficient state very less among the subjects in whom they were studying autoimmunity which was heightened [24]. Likewise, it is observed that iodine supplementation, when in excess, may cause iodine-induced hyperthyroidism [25, 26]. However, functional status was not evaluated in the present study; therefore, if any functional aberration was there at all, that was beyond the scope for discrimination in this study.

There was no difference of UI between goitrous and nongoitrous mothers, and in both groups, median values of UI were much high. Therefore, the presence of goiter in these mothers is unlikely to be attributable to iodine deficient state. However, frequency of goiter was around 15% among the subjects. Unlike the present findings, some investigators observed a bit higher frequencies of goiter among lactating mothers [27]; but, they also followed that frequency of deficient iodine status was minimum among goitrous subjects which virtually complies with the present findings. In this group, goiter may be related to the persistence of the physiological enlargement of thyroid size in pregnancy, to autoimmunity or unidentified goitrogen. Family history for thyroid diseases was less frequent, most subjects were housewives, indwelling inside Dhaka, socioeconomically good or average and virtually all subjects taking packet salt. Limited numbers of studies are there who did not find any remarkable link of iodine status with the demographic profile [16, 28].

We observed that none of the variables had significant predictive power over the deficient state of iodine. Persistent supplementation of iodized salt is needed to sustain a maintenance level of iodine nutrition status in the breastfeeding mothers.

For convenience of sample collection, the study included healthy breastfeeding mothers visiting the hospital as attendants and not seeking medical care for themselves. The true reflection of the community needs random sampling from different parts of the country and as such the present study may not reflect the iodine nutrition status of breastfeeding mothers of the community. We used Sandell–Kolthoff reaction for estimating UI. Despite being reliable and feasible, this method has some loopholes. There may be interference by other ions and the extreme values of UI may erroneously produce similar reading [29].

5. Conclusions

The present study observed that deficient iodine nutrition is not frequent among breastfeeding mothers. Although age, socioeconomic condition, and awareness of iodine have a positive impact, none may be good predictors for assessment over iodine nutrition status of lactating mothers.

Data Availability

The data used to support the findings of this study are available from the corresponding author upon request.

Conflicts of Interest

The authors declare that there are no conflicts of interest regarding the publication of this paper.

Acknowledgments

The authors thankfully acknowledge the technical contribution of Designated Reference Institute of Chemical Measurements (DRiCM), Dhaka, Bangladesh. The participants of the study and colleagues in the Department of Endocrinology, BSMMU are also acknowledged.

References

A. Melse-Bunstra and N. Jaiswal, “Iodine deficiency in pregnancy, infancy and childhood and its consequences for brain development,” Best Practice & Research Clinical Endocrinology & Metabolism, vol. 24, no. 1, pp. 29–38, 2010.

J. G. Dorea, “Iodine nutrition and breast feeding,” Journal of Trace Elements in Medicine and Biology, vol. 16, no. 4, pp. 207–220, 2002.

R. D. Semba and F. Delange, “Iodine in human milk: perspectives for infant health,” Nutrition Reviews, vol. 59, no. 8, pp. 269–278, 2009.

D. K. Dror and L. H. Allen, “Iodine in human milk: a systematic review,” Advances in Nutrition, vol. 9, no. suppl_1, pp. 347S–357S, 2018.

WHO, UNICEF, and ICCIDD, Assessment of Iodine Deficiency Disorders and Monitoring their Elimination, a Guide for Programme Managers, WHO, Geneva, Switzerland, 3rd edition, 2007.

K. Bougma, F. Aboud, K. Harding, and G. Marquis, “Iodine and mental development of children 5 years old and under: a systematic review and meta-analysis,” Nutrients, vol. 5, no. 4, pp. 1384–1416, 2013.

H. K. Yusuf, A. M. Rahman, F. P. Chowdhury et al., “Iodine deficiency disorders in Bangladesh, 2004-05: ten years of iodized salt intervention brings remarkable achievement in lowering goitre and iodine deficiency among children and women,” Asia Pacific Journal of Clinical Nutrition, vol. 17, no. 4, pp. 620–628, 2008.

WHO secretariat, M. Andersson, B. de Benoit, F. Delange, and J. Zupan, “Prevention and control of iodine deficiency in pregnant and lactating women and in children less than two years old: conclusions and recommendations of the technical consultation,” Public Health Nutrition, vol. 10, no. 12A, pp. 1606–1611, 2007.

M. B. Zimmermann and M. Andersson, “Assessment of iodine nutrition in populations: past, present, and future,” Nutrition Reviews, vol. 70, no. 10, pp. 553–570, 2012.

M. B. Zimmermann, P. L. Jooste, and C. S. Pandav, “Iodine-deficiency disorders,” The Lancet, vol. 372, no. 9645, pp. 1251–1262, 2008.

P. Nazeri, H. Dalili, Y. Mehrabi, M. Hedayati, P. Mirmiran, and F. Azizi, “Breast milk iodine concentration rather than maternal urinary iodine is a reliable indicator for monitoring iodine status of breastfed neonates,” Biological Trace Element Research, vol. 185, no. 1, pp. 71–77, 2018.

M. B. Zimmermann, “Iodine deficiency,” Endocrine Reviews, vol. 30, no. 4, pp. 376–408, 2009.

E. B. Sandell and I. M. Kolthoff, “Micro determination of iodine by a catalytic method,” Mikrochimica Acta, vol. 1, no. 1, pp. 9–25, 1937.

R. S. Rao, R. Kamath, A. Das, N. S. Nair, and Keshavamurthy, “Prevalence of goitre among school children in coastal Karnataka,” The Indian Journal of Pediatrics, vol. 69, no. 6, pp. 477–479, 2002.

G. M. Molla, M. I. Arslan, F. H. Mollah, M. A. H. Khan, and C. M. K. Jinnah, “Urinary iodine excretion of lactating mothers predicts the iodine content of their breast milk,” Journal of Enam Medical College, vol. 1, no. 1, pp. 15–18, 2012.

H. Sadon, Y. Moussa, M. M. Alma, and H. Daouda, “Iodine status of breastfed infants and their mothers after sixteen years of universal dietary salt iodization program in Dosso, Niger,” The Open Nutrition Journal, vol. 7, no. 1, pp. 7–12, 2013.

A. Majumder, A. Jaiswal, and S. Chatterjee, “Prevalence of iodine deficiency among pregnant and lactating women: experience in Kolkata,” Indian Journal of Endocrinology and Metabolism, vol. 18, no. 4, pp. 486–490, 2014.

H. M. Mulrine, S. A. Skeaff, E. L. Ferguson, A. R. Gray, and P. Valeix, “Breast-milk iodine concentration declines over the first 6 mo postpartum in iodine-deficient women,” The American Journal of Clinical Nutrition, vol. 92, no. 4, pp. 849–856, 2010.

E. Speller, W. Broderibb, and E. Mcguire, “Breast feeding and thyroid disease: a literature review,” Journal of Australian Breastfeeding Association, vol. 20, pp. 1–12, 2012.

V. J. Temple, R. Oge, I. Daphne et al., “Salt iodization and iodine status among infants and lactating mothers in Papua New Guniea,” African Journal of Food, Agriculture, Nutrition and Development, vol. 9, pp. 1807–1809, 2009.

D. Sukkhojaiwaratkul, P. Mahachoklertwattana, P. Poomthavorn et al., “Effects of maternal iodine supplementation during pregnancy and lactation on iodine status and neonatal thyroid-stimulating hormone,” Journal of Perinatology, vol. 34, no. 8, pp. 594–598, 2014.

S. R. Mallard and L. A. Houghton, “Public health policy to redress iodine insufficiency in pregnant women may widen sociodemographic disparities,” Public Health Nutrition, vol. 17, no. 6, pp. 1421–1429, 2014.

N. Pal, S. K. Samanta, A. Chakraborty, N. K. Chandra, and A. K. Chandra, “Interrelationship between iodine nutritional status of lactating mothers and their absolutely breast-fed infants in coastal districts of Gangetic West Bengal in India,” European Journal of Pediatrics, vol. 177, no. 1, pp. 39–45, 2018.

M. A. Hasanat, M. A. Rumi, M. N. Alam et al., “Urinary iodine status and thyroid dysfunction: a Bangladesh perspective,” Bangladesh Medical Research Council Bulletin, vol. 30, no. 1, pp. 16–24, 2004.

C. H. Todd, T. Allain, Z. A. R. Gomo, J. A. Hasler, M. Ndiweni, and E. Oken, “Increase in thyrotoxicosis associated with iodine supplements in Zimbabwe,” The Lancet, vol. 346, no. 8989, pp. 1563-1564, 1995.

J. B. Stawbury, A. E. Ermans, P. Bourdoux et al., “Iodine induced hyperthyroidism: occurrence and epidemiology,” Thyroid, vol. 8, no. 1, pp. 83–100, 1998.

H. R. Bazrafshan, S. Mohammadian, A. Ordookhani et al., “An assessment of urinary and breast milk iodine concentrations in lactating mothers from Gorgan, Iran, 2003,” Thyroid, vol. 15, no. 10, pp. 1165–1168, 2005.

F. Azizi and P. Smyth, “Breastfeeding and maternal and infant iodine nutrition,” Clinical Endocrinology, vol. 70, no. 5, pp. 803–809, 2009.

M. A. Hasanat, M. A. Rumi, M. N. Alam et al., “Antithyroid antibodies, urinary iodine and thyroid hormones in clinically suspected endemic goitre,” Journal of Diabetes and Endocrinology, vol. 26, pp. 3–10, 1998.