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Subclinical Hypothyroidism and Elevated Thyroglobulin in Infants with Chronic Excess Iodine Intake.
Thyroid. 2015 Jul; 25(7):851-9.T

Abstract

BACKGROUND

Acute iodine excess in newborns can cause hypothyroidism, but there are limited data on the effects of iodine excess on thyroid function in older infants. The aim of this study was to measure the effects of chronic excess iodine intake on thyroid function in 6-24-month-old infants.

METHODS

In this cross-sectional study, infants (n=696) in eastern Nepal were studied. Spot urine samples, venous blood samples, and household salt samples were collected, and urinary iodine concentration (UIC), serum free thyroxine (fT4), thyrotropin (TSH), thyroglobulin (Tg), and titrated household salt iodine concentration (SIC) were measured. Daily iodine intake was calculated from UIC based on estimates of urine volume at this age.

RESULTS

Median (25th-75th percentile) household SIC was 89 (70-149) ppm, while national legislation stipulates a fortification level of 50 ppm. Median UIC was 407 (312-491) μg/L; 76% of infants had a UIC >300 μg/L, suggesting iodine excess. Calculated mean iodine intake in 12-24-month-old infants was 220 μg/day, exceeding the recommended safe upper limit for iodine at this age (200 μg/day). Among the infants, 15.8% had an elevated Tg, 7.4% had subclinical hypothyroidism, but <1% had overt hypothyroidism. UIC was not a significant predictor of thyroid function, thyroid hormones, or Tg.

CONCLUSION

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.

Authors+Show Affiliations

1 Department of Biochemistry, B.P. Koirala Institute of Health Sciences , Dharan, Nepal .1 Department of Biochemistry, B.P. Koirala Institute of Health Sciences , Dharan, Nepal .1 Department of Biochemistry, B.P. Koirala Institute of Health Sciences , Dharan, Nepal .2 Department of Pediatric and Adolescent Medicine, B.P. Koirala Institute of Health Sciences , Dharan, Nepal .1 Department of Biochemistry, B.P. Koirala Institute of Health Sciences , Dharan, Nepal .3 Human Nutrition Laboratory, Institute of Food Nutrition and Health, Swiss Federal Institute of Technology (ETH) , Zurich, Switzerland .3 Human Nutrition Laboratory, Institute of Food Nutrition and Health, Swiss Federal Institute of Technology (ETH) , Zurich, Switzerland .

Pub Type(s)

Journal Article
Research Support, Non-U.S. Gov't

Language

eng

PubMed ID

25950720

Citation

Nepal, Ashwini Kumar, et al. "Subclinical Hypothyroidism and Elevated Thyroglobulin in Infants With Chronic Excess Iodine Intake." Thyroid : Official Journal of the American Thyroid Association, vol. 25, no. 7, 2015, pp. 851-9.
Nepal AK, Suwal R, Gautam S, et al. Subclinical Hypothyroidism and Elevated Thyroglobulin in Infants with Chronic Excess Iodine Intake. Thyroid. 2015;25(7):851-9.
Nepal, A. K., Suwal, R., Gautam, S., Shah, G. S., Baral, N., Andersson, M., & Zimmermann, M. B. (2015). Subclinical Hypothyroidism and Elevated Thyroglobulin in Infants with Chronic Excess Iodine Intake. Thyroid : Official Journal of the American Thyroid Association, 25(7), 851-9. https://doi.org/10.1089/thy.2015.0153
Nepal AK, et al. Subclinical Hypothyroidism and Elevated Thyroglobulin in Infants With Chronic Excess Iodine Intake. Thyroid. 2015;25(7):851-9. PubMed PMID: 25950720.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Subclinical Hypothyroidism and Elevated Thyroglobulin in Infants with Chronic Excess Iodine Intake. AU - Nepal,Ashwini Kumar, AU - Suwal,Ranjan, AU - Gautam,Sharad, AU - Shah,Gauri Shankar, AU - Baral,Nirmal, AU - Andersson,Maria, AU - Zimmermann,Michael Bruce, Y1 - 2015/06/01/ PY - 2015/5/8/entrez PY - 2015/5/8/pubmed PY - 2016/4/7/medline SP - 851 EP - 9 JF - Thyroid : official journal of the American Thyroid Association JO - Thyroid VL - 25 IS - 7 N2 - BACKGROUND: Acute iodine excess in newborns can cause hypothyroidism, but there are limited data on the effects of iodine excess on thyroid function in older infants. The aim of this study was to measure the effects of chronic excess iodine intake on thyroid function in 6-24-month-old infants. METHODS: In this cross-sectional study, infants (n=696) in eastern Nepal were studied. Spot urine samples, venous blood samples, and household salt samples were collected, and urinary iodine concentration (UIC), serum free thyroxine (fT4), thyrotropin (TSH), thyroglobulin (Tg), and titrated household salt iodine concentration (SIC) were measured. Daily iodine intake was calculated from UIC based on estimates of urine volume at this age. RESULTS: Median (25th-75th percentile) household SIC was 89 (70-149) ppm, while national legislation stipulates a fortification level of 50 ppm. Median UIC was 407 (312-491) μg/L; 76% of infants had a UIC >300 μg/L, suggesting iodine excess. Calculated mean iodine intake in 12-24-month-old infants was 220 μg/day, exceeding the recommended safe upper limit for iodine at this age (200 μg/day). Among the infants, 15.8% had an elevated Tg, 7.4% had subclinical hypothyroidism, but <1% had overt hypothyroidism. UIC was not a significant predictor of thyroid function, thyroid hormones, or Tg. CONCLUSION: 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. SN - 1557-9077 UR - https://www.unboundmedicine.com/medline/citation/25950720/Subclinical_Hypothyroidism_and_Elevated_Thyroglobulin_in_Infants_with_Chronic_Excess_Iodine_Intake_ L2 - https://www.liebertpub.com/doi/full/10.1089/thy.2015.0153?url_ver=Z39.88-2003&amp;rfr_id=ori:rid:crossref.org&amp;rfr_dat=cr_pub=pubmed DB - PRIME DP - Unbound Medicine ER -