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Effect of iodine restriction on thyroid function in subclinical hypothyroid patients in an iodine-replete area: a long period observation in a large-scale cohort.
Thyroid. 2014 Sep; 24(9):1361-8.T

Abstract

BACKGROUND

Excessive iodine intake is related to a higher prevalence of hypothyroidism, including subclinical hypothyroidism (SCH), in iodine-replete areas. This study aimed to evaluate the effect of iodine restriction on thyroid function in SCH patients in an iodine-replete area and analyze the relationship between serum thyrotropin (TSH) levels and iodine intake.

METHODS

The study consisted of 146 consecutive patients who were diagnosed with SCH at the Samsung Medical Center between 2010 and 2012. Urinary iodine concentration (UIC) was measured in 82 patients. Of these, 20 patients with UIC < 300 μg/L were excluded, and 62 patients with UIC ≥ 300 μg/L were educated about the restriction of iodine-rich foods. Following the first follow-up visit, these patients were divided into two groups based on the UIC level: group A (well-controlled iodine intake, UIC < 300 μg/L, n = 40), and group B (poorly controlled iodine intake, UIC ≥ 300 μg/L, n = 22). The remaining 64 patients did not restrict iodine rich foods (group C). The 82 patients with measured UICs were reevaluated every 3-6 months, and the median follow-up was 13 months (range 3-32 months). Thyroid function and UIC were measured at each visit. The correlation between serum TSH level and UIC was determined for the 82 patients in whom UIC was measured.

RESULTS

Following 3-6 months of iodine restriction, the serum TSH levels significantly decreased in group A (from 9.0 mU/L to 4.7 mU/L; p < 0.01). In addition, the serum free thyroxine (T4) levels in group A significantly increased (from 1.11 ± 0.23 ng/dL to 1.18 ± 0.17 ng/dL; p < 0.05). However, there were no significant changes in serum TSH or free T4 levels in groups B and C. Serum TSH levels significantly correlated with UIC (r = 0.33, p < 0.01).

CONCLUSION

Iodine restriction may normalize or, at the very least, decrease serum TSH levels in SCH patients, and serum TSH levels are strongly correlated with UIC. Therefore, restriction of iodine intake could be a primary treatment option in SCH patients in an iodine-replete area.

Authors+Show Affiliations

Department of Medicine, Division of Endocrinology and Metabolism, Thyroid Center, Samsung Medical Center, Sungkyunkwan University School of Medicine , Seoul, Korea.No affiliation info availableNo affiliation info availableNo affiliation info availableNo affiliation info availableNo affiliation info availableNo affiliation info availableNo affiliation info available

Pub Type(s)

Journal Article

Language

eng

PubMed ID

24892764

Citation

Joung, Ji Young, et al. "Effect of Iodine Restriction On Thyroid Function in Subclinical Hypothyroid Patients in an Iodine-replete Area: a Long Period Observation in a Large-scale Cohort." Thyroid : Official Journal of the American Thyroid Association, vol. 24, no. 9, 2014, pp. 1361-8.
Joung JY, Cho YY, Park SM, et al. Effect of iodine restriction on thyroid function in subclinical hypothyroid patients in an iodine-replete area: a long period observation in a large-scale cohort. Thyroid. 2014;24(9):1361-8.
Joung, J. Y., Cho, Y. Y., Park, S. M., Kim, T. H., Kim, N. K., Sohn, S. Y., Kim, S. W., & Chung, J. H. (2014). Effect of iodine restriction on thyroid function in subclinical hypothyroid patients in an iodine-replete area: a long period observation in a large-scale cohort. Thyroid : Official Journal of the American Thyroid Association, 24(9), 1361-8. https://doi.org/10.1089/thy.2014.0046
Joung JY, et al. Effect of Iodine Restriction On Thyroid Function in Subclinical Hypothyroid Patients in an Iodine-replete Area: a Long Period Observation in a Large-scale Cohort. Thyroid. 2014;24(9):1361-8. PubMed PMID: 24892764.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Effect of iodine restriction on thyroid function in subclinical hypothyroid patients in an iodine-replete area: a long period observation in a large-scale cohort. AU - Joung,Ji Young, AU - Cho,Yoon Young, AU - Park,Sun-Mi, AU - Kim,Tae Hun, AU - Kim,Na Kyung, AU - Sohn,Seo Young, AU - Kim,Sun Wook, AU - Chung,Jae Hoon, Y1 - 2014/06/30/ PY - 2014/6/4/entrez PY - 2014/6/4/pubmed PY - 2015/11/6/medline SP - 1361 EP - 8 JF - Thyroid : official journal of the American Thyroid Association JO - Thyroid VL - 24 IS - 9 N2 - BACKGROUND: Excessive iodine intake is related to a higher prevalence of hypothyroidism, including subclinical hypothyroidism (SCH), in iodine-replete areas. This study aimed to evaluate the effect of iodine restriction on thyroid function in SCH patients in an iodine-replete area and analyze the relationship between serum thyrotropin (TSH) levels and iodine intake. METHODS: The study consisted of 146 consecutive patients who were diagnosed with SCH at the Samsung Medical Center between 2010 and 2012. Urinary iodine concentration (UIC) was measured in 82 patients. Of these, 20 patients with UIC < 300 μg/L were excluded, and 62 patients with UIC ≥ 300 μg/L were educated about the restriction of iodine-rich foods. Following the first follow-up visit, these patients were divided into two groups based on the UIC level: group A (well-controlled iodine intake, UIC < 300 μg/L, n = 40), and group B (poorly controlled iodine intake, UIC ≥ 300 μg/L, n = 22). The remaining 64 patients did not restrict iodine rich foods (group C). The 82 patients with measured UICs were reevaluated every 3-6 months, and the median follow-up was 13 months (range 3-32 months). Thyroid function and UIC were measured at each visit. The correlation between serum TSH level and UIC was determined for the 82 patients in whom UIC was measured. RESULTS: Following 3-6 months of iodine restriction, the serum TSH levels significantly decreased in group A (from 9.0 mU/L to 4.7 mU/L; p < 0.01). In addition, the serum free thyroxine (T4) levels in group A significantly increased (from 1.11 ± 0.23 ng/dL to 1.18 ± 0.17 ng/dL; p < 0.05). However, there were no significant changes in serum TSH or free T4 levels in groups B and C. Serum TSH levels significantly correlated with UIC (r = 0.33, p < 0.01). CONCLUSION: Iodine restriction may normalize or, at the very least, decrease serum TSH levels in SCH patients, and serum TSH levels are strongly correlated with UIC. Therefore, restriction of iodine intake could be a primary treatment option in SCH patients in an iodine-replete area. SN - 1557-9077 UR - https://www.unboundmedicine.com/medline/citation/24892764/Effect_of_iodine_restriction_on_thyroid_function_in_subclinical_hypothyroid_patients_in_an_iodine_replete_area:_a_long_period_observation_in_a_large_scale_cohort_ L2 - https://www.liebertpub.com/doi/full/10.1089/thy.2014.0046?url_ver=Z39.88-2003&amp;rfr_id=ori:rid:crossref.org&amp;rfr_dat=cr_pub=pubmed DB - PRIME DP - Unbound Medicine ER -