Subclinical Hypothyroidism and Elevated Thyroglobulin in Infants with Chronic Excess Iodine Intake

Nepal, Ajit; Suwal, Ranjan; Gautam, Swotantra; Shah, G. L.; Baral, Nirmal; Andersson, Maria; Zimmermann, Michael

doi:10.1089/thy.2015.0153

Cited by 24 publications

(37 citation statements)

References 38 publications

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“…Twenty-three papers reported cross-sectional studies in children [41, 43–64], of which 14 papers mainly reported thyroid diseases [41, 46, 47–49, 51–55, 56–58, 60], four reported biomarkers [61–64] and five described both [43–45, 50, 59] (Tables 5 and 6). Except for Nepal et al .…”

Section: Resultsmentioning

confidence: 99%

“…Except for Nepal et al . in infants [43], most studies were in school-age children. Water was a cause of excess iodine status in ten papers, from China [44–48, 52, 58, 59], refugee camps in Africa [53] and Somalia [41].…”

Section: Resultsmentioning

confidence: 99%

“…Fortified food might have been a cause in two papers, from Sudan [51] and the USA [60], while seafood consumption might have been the cause in one paper from Japan [57]. The cause was not clearly described in others [43, 50] or was not assessed because median UIC was not excessive [61–64]. …”

Section: Resultsmentioning

confidence: 99%

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Effect of excess iodine intake on thyroid diseases in different populations: A systematic review and meta-analyses including observational studies

et al. 2017

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BackgroundAlthough several reports concerning the association of iodine excess and thyroid disease have appeared, no systematic review of the association between iodine excess intake and thyroid diseases, especially hyperthyroidism and hypothyroidism, has yet been reported.MethodWe conducted a systematic search of Ovid MEDLINE, PubMed, Cochrane Central Register of Controlled Trials databases, Ichushi-Web and CiNii database for intervention trials and observational studies. Search terms were constructed from related words for excess AND iodine intake or excretion AND thyroid hormones or diseases AND study designs. After considering the qualitative heterogeneity among studies, a meta-analysis was conducted and odds ratios and 95% confidence intervals (CI) were estimated in random-effects models. A protocol was registered with PROSPERO (No. CRD42015028081).Results50 articles were included, including three intervention trials, six case-control studies, six follow-up studies and 35 cross-sectional studies. Three cross-sectional studies in adults included in meta-analysis. Odds ratio of overt and subclinical hypothyroidism between excess and adequate populations were 2.78 (CI:1.47 to 5.27) and 2.03 (CI:1.58 to 2.62) in adults, respectively. Source of excess iodine status was mainly iodized salt or water in included studies.ConclusionAlthough universal salt iodization has improved goiter rates, chronic exposure to excess iodine from water or poorly monitored salt are risk factors for hypothyroidism in free-living populations. Monitoring of both iodine concentration in salt as well as the iodine concentration in local drinking water are essential to preventing thyroid diseases. Hypothyroidism should be also carefully monitored in areas with excess iodine. Because of the low quality and limited number of included studies, further evidence and review are required.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

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Effect of excess iodine intake on thyroid diseases in different populations: A systematic review and meta-analyses including observational studies

et al. 2017

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“…A limitation of this study is that we did not present thyroid hormones or thyroglobulin (44,45) to determine whether thyroid function was affected by high iodine intakes. In conclusion, our findings suggest that the safe upper iodine intake ranges for children aged 7-10 and 11-14 y are 150-249 and 150-299 mg/d, respectively.…”

Section: Discussionmentioning

confidence: 99%

Associations between iodine intake, thyroid volume, and goiter rate in school-aged Chinese children from areas with high iodine drinking water concentrations

Chen

et al. 2017

The American Journal of Clinical Nutrition

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Background: Excessive iodine intake may have adverse effects on the thyroid, particularly in children, but the safe upper iodine intake concentration in children is unclear. Objective: We assessed the adverse effects of high iodine intake from iodine-rich drinking water on thyroid size in children by examining associations between thyroid volume (Tvol), total goiter rate (TGR), and iodine intake. Design: In a multistage cross-sectional survey, we collected two 24-h urine samples on 2 nonconsecutive days and determined 24-h urinary iodine excretion, then calculated habitual daily iodine intake. Ultrasonographic Tvol was measured, and TGR was calculated based on international and Chinese reference ranges for Tvol in children.Results: This study included 2089 children from Shandong province, where the median (IQR) drinking water iodine concentration was 183 mg/L (69-406 mg/L). The median (IQR) 24-h urinary iodine concentrations for the 2 collections were 381 mg/L (203-649 mg/L) and 398 mg/L (202-687 mg/L), respectively. The median (IQR) habitual daily iodine intake of children was 298 mg/d (186-437 mg/d). Tvols were slightly higher in boys than in girls (P = 0.035). The overall TGR was 9.7% and did not differ by sex. The TGR was w5% for children aged 7-10 and 11-14 y at iodine intakes of 200-249 and 250-299 mg/d, respectively. With the use of logistic regression and 2-step linear regression, a nonlinear association was observed between Tvol, TGR, and iodine intake, with a threshold intake of 150 mg/d. Conclusions: Tvol begins to increase in children when iodine intake is $150 mg/d, and the TGR exceeds 5% when daily iodine intake is $250 mg/d for children aged 7-10 y and $300 mg/d for children aged 11-14 y. Our findings suggest that 150-249 and 150-299 mg/d seem to be safe upper iodine intake ranges for children aged 7-10 and 11-14 y, respectively. This trial was registered at clinicaltrials.gov as NCT02915536.Am J Clin Nutr 2017;105:228-33.

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“…Acute iodine excess from for example maternal iodine supplements and iodine containing skin disinfectants may cause hypothyroidism in newborns (6,7). Recent data indicate that older infants may be able to adapt to high iodine intakes and maintain their euthyroid state (8). However, little is known about the effects of habitual high iodine intake on thyroid function in breastfed infants.…”

Section: Introductionmentioning

confidence: 99%

Breast-Milk Iodine Concentrations, Iodine Status, and Thyroid Function of Breastfed Infants Aged 2-4 Months and Their Mothers Residing in a South African Township

Osei

Andersson²,

Reijden³

et al. 2016

Jcrpe

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Objective:Lactating women and their infants are susceptible to iodine deficiency and iodine excess. In South Africa, no data exist on the iodine status and thyroid function of these vulnerable groups.Methods:In a cross-sectional study, urinary iodine concentrations (UIC), thyroid function, and breast-milk iodine concentrations (BMIC) were assessed in 100 lactating women from a South African township and their 2-4-month-old breastfed infants. Potential predictors of UIC, thyroid function, and BMIC, including household salt iodine concentrations (SIC) and maternal sodium excretion, were also investigated.Results:The median (25th-75th percentile) UIC was 373 (202-627) μg/L in infants and 118 (67-179) μg/L in mothers. Median household SIC was 44 (27-63) ppm. Household SIC and maternal urinary sodium excretion predicted UIC of lactating mothers. Median BMIC was 179 (126-269) μg/L. Age of infants, SIC, and maternal UIC predicted BMIC. In turn, infant age and BMIC predicted UIC of infants. Forty-two percent of SIC values were within the South African recommended salt iodine fortification level at production of 35-65 ppm, whilst 21% of SIC were >65 ppm. Thyroid-stimulating hormone, total thyroxine, and thyroglobulin concentrations in the dried whole blood spot specimens from the infants were 1.3 (0.8-1.9) mU/L, 128±33 mmol/L, and 77.1 (56.3-105.7) μg/L, respectively, and did not correlate with infant UIC or BMIC.Conclusion:Our results suggest that the salt fortification program in South Africa provides adequate iodine to lactating women and indirectly to their infants via breast milk. However, monitoring of salt iodine content of the mandatory salt iodization program in South Africa is important to avoid over-iodization of salt.

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Subclinical Hypothyroidism and Elevated Thyroglobulin in Infants with Chronic Excess Iodine Intake

Abstract: In 6-24-month-old infants exposed to excessive iodine intake, ∼7% have subclinical hypothyroidism but <1% have overt hypothyroidism. These findings suggest the thyroid in late infancy is already able to adapt to high iodine intakes and, in most cases, maintain euthyroidism.

Cited by 24 publications

References 38 publications

Effect of excess iodine intake on thyroid diseases in different populations: A systematic review and meta-analyses including observational studies

Effect of excess iodine intake on thyroid diseases in different populations: A systematic review and meta-analyses including observational studies

Associations between iodine intake, thyroid volume, and goiter rate in school-aged Chinese children from areas with high iodine drinking water concentrations

Breast-Milk Iodine Concentrations, Iodine Status, and Thyroid Function of Breastfed Infants Aged 2-4 Months and Their Mothers Residing in a South African Township

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