Excessive iodine intake and subclinical hypothyroidism in children and adolescents aged 6-19 years: results of the sixth Korean National Health and Nutrition Examination Survey (KNHANES), 2013-2015.

Excessive iodine intake and subclinical hypothyroidism in children and adolescents aged 6-19 years: results of the sixth Korean National Health and Nutrition Examination Survey (KNHANES), 2013-2015.

Thyroid. 2018 May 08;:

Authors: Kang MJ, Hwang IT, Chung HR

Abstract
BACKGROUND: Iodine is an important element for the thyroid hormone production, and its deficiency or excessive intake is associated with various thyroid diseases. Little is known about the association between iodine status and thyroid function among children and adolescents living in iodine-rich areas, therefore, we analyzed this association using data from a nationwide survey.
METHODS: From the Korea National Health and Nutrition Examination Surveys (KNHANES) VI (2013-2015) data, 1288 subjects (711 male) aged 6-19 years who underwent urinary iodine concentration (UIC) test and 1000 subjects (564 male) aged 10-19 years who underwent thyroid function test were included in this study. Serum levels of thyroid stimulating hormone (TSH), free thyroxine (T4), and thyroperoxidase antibody (TPO-Ab) were analyzed. Subclinical hypothyroidism (SCH) was defined as TSH >5.5 µIU/mL with a normal free T4 level. Daily iodine intake was calculated from the UIC. Daily sodium intake was reviewed from the nutritional survey data of 1181 subjects.
RESULTS: The median (ranges) of UIC was 449 (15-21,905) µg/L and prevalence of UIC ≥300 µg/L was 64.9% and UIC ≥1000 µg/L was 25.0%. The prevalence of sodium intake >2000 mg/day and iodine intake >2400 µg/day was 75.0% (885/1181) and 12.7% (164/1288), respectively. The prevalence of SCH and TPO-Ab >34 IU/mL was 7.2% (72/1000) and 2.3% (23/1000), respectively. The prevalence of SCH was significantly higher in the iodine deficiency and iodine excessive groups compared to those in the UIC 100-299.9 µg/L group (P = 0.038); therefore, there was the U-shape and inverted U-shape correlations between serum levels of TSH and free T4 with UIC, respectively. These correlations showed especially prominent when UIC was >1000 µg/L. There was no definite correlation between TPO-Ab and UIC.
CONCLUSIONS: Excess iodine was prevalent in Korean children and adolescents, which may result in SCH. Therefore, the monitoring of iodine status and education on adequate intake are needed in iodine-rich areas.

PMID: 29737233 [PubMed - as supplied by publisher]

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