Amelioration of iodine supply is notably associated with thyroid function in healthy subjects and in patients with euthyroid Hashimoto’s thyroiditis
Abstract
Background: Our aim was to establish how healthy subjects (HS) and patients with euthyroid Hashimoto's thyroiditis (EuHT) faced the increase in mandatory salt iodization in Slovenia in 1999 from previous 10 mg of potassium iodide to 25 mg per kg since data about thyroid function with respect to iodine supply are scant.
Methods: In this retrospective study we reviewed records of 24,899 patients referred for the first time between 1995 and 2002 to our tertiary referral centre with a stable catchment area for more than 20 years. HS were negative and patients with EuHT positive for thyroid peroxidase antibodies and/or thyroglobulin antibodies. Thyrotropin (TSH), free thyroxine (fT4), and free triiodothyronine (fT3) levels were obtained. The fT4/fT3 ratio was calculated.
Results: In the period 1995-1998, 917 HS had significantly lower fT4/fT3 ratio than 644 HS in the period 1999-2002 (2.6±0.6 and 2.9±0.9, respectively, p<0.001) on account of significantly higher fT3 (median 5.7 and 5.2 pmol/L, p<0.001). Similarly, in 1995-1998, 482 patients with EuHT had a lower fT4/fT3 ratio than 846 EuHT in 1999-2002 (2.4±0.6 and 2.8±0.7, respectively, p<0.001) on account of significantly higher fT3 (median 5.8 and 4.9, respectively, p=0.018). HS had a higher fT4/fT3 ratio than patients with EuHT in 1995-1998 but not in 1999-2002 (p<0.001 and p=0.206, respectively).
Conclusions: Amelioration of iodine supply is associated with an increase in the fT4/fT3 ratio on account of lower fT3, and with a similar thyroid function in HS and in patients with EuHT.
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Bülow Pedersen I, Knudsen N, Jørgensen T, Perrild H, Ovesen L, Laurberg P. Large differences in incidence of overt hyper- and hypothyroidism associated with a small difference in iodine intake: a prospective comparative register-based population survey. J Clin Endocrinol Metab. 2002; 87 (10): 4462-4469.
Laurberg P, Bülow Pedersen I, Knudsen N, Ovesen L, Andersen S. Environmental iodine intake affects the type of nonmalignant thyroid disease. Tyroid. 2001; 11 (5): 457-69.
Laurberg P, Cerqueira C, Ovesen L, Rasmussen LB, Perrild H, Andersen S, et al. Iodine intake as a determinant of thyroid disorders in populations. Best Prac Res Clin Endocrinol Metab. 2010; 24 (1): 13-27.
Zaletel K, Gaberšček S, Pirnat E, Krhin B, Hojker S. Ten-year follow-up thyroid epidemiology in Slovenia afer increase in salt iodization. Croat Med J. 2011; 52 (5): 615-21.
Zimmermann MB. Iodine defciency. Endocr Rev. 2009; 30 (4): 376-408.
Gaberšček S, Bajuk V, Zaletel K, Pirnat E, Hojker S. Benefcial effects of adequate iodine supply on charateristics of thyroid autonomy. Clin Endocrinol (Oxford). 2013; 79 (6): 867-73.
Heydarian P, Ordookhani A, Azizi F. Goiter rate, serum thyrotropin, thyroid autoantibodies and urinary iodine concentration in Tehranian adults before and afer national salt iodization. J Endocrinol Invest. 2007; 30 (5): 404-10.
Doufas AG, Mastorakos G, Chatziioannou S, Tseleni-Balafouta S, Piperingos G, Boukis MA, et al. Te predominant form of non-toxic goiter in Greece in now autoimmune thyroiditis. Eur J Endocrinol. 1999; 140 (6): 505-11.
Papanastasiou L, Vatalas IA, Koutras DA, Mastorakos G. Tyroid autoimmunity in the current iodine environment. Tyroid. 2007; 17 (8): 729-39.
Okosieme OE, Premawardhana LD, Jayasinghe A, Kaluarachi WN, Parkes AB, Smyth PP, et al. Tyroglobulin autoantibodies in iodized subjects: relationship between epitope specifcities and longitudinal antibody activity. Tyroid. 2005; 15 (9): 1067-72.
Zois C, Stavrou I, Svarna E, Seferiadis K, Tsatsoulis A. Natural course of autoimmune thyroiditis afer elimination of iodine defciency in northwestern Greece. Tyroid. 2006; 16 (3): 289-93.
Vitti P & Aghini-Lombardi F. Te effect of 15 years voluntary iodine prophylaxis through iodized salt in a small rural community: the Pescopagano experience. Ann Endocrinol (Paris). 2011; 72 (2): 162-3.
Laurberg P, Pedersen KM, Hreidarsson A, Sigfusson N, Iversen E, Knudsen PR. Iodine intake and the pattern of thyroid disorders: a comparative epidemiological study of thyroid abnormalities in the elderly in Iceland and in Jutland, Denmark. J Clin Endocrinol Metab. 1998; 83 (3): 765-9.
Hintze G, Burghardt U, Baumert J, Windeler J, Köbberling J. Prevalence of thyroid dysfunction in elderly subjects from the general population in an iodine defciency area. Aging (Milano). 1991; 3 (4): 325-31.
Hollowell JG, Staehling NW, Flanders WD, Hannon WH, Gunter EW, Spencer CA, et al. Serum TSH, T(4), and thyroid antibodies in the United States population (1988 to 1994); National Health and Nutritrion Examination Survey (NHANES III). J Clin Endocrinol Metab. 2002; 87 (2): 489-99.
Maia AL, Kim BW, Huang SA, Harney JW, Larsen PR. Type 2 iodothyronine deiodinase is the major source of plasma T3 in euthyroid humans. J Clin Invest. 2005; 115 (9): 2524-33.
Fisher DA. Physiological variations in thyroid hormones: physiological and pathophysiological considerations. Clin Chem. 1996; 42 (1): 135-9.
Mortoglou A, Candiloros H. Te serum triiodothyronine to thyroxine (T3/T4) ratio in various thyroid disorders and afer Levothyroxine replacement therapy. Hormones. 2004; 3 (2): 120-6.
Grmek J, Gaberšček S, Biček A, Zaletel K. Usefulness of free thyroxine to free triiodothyronine ratio for diagnostics of various types of hyperthyroidism. Zdrav Vestn. 2015; 84 (5): 366-72.
Zimmermann MB, Jooste PL, Pandav CS. Iodine-defciency disorders. Lancet. 2008; 372 (9645): 1251-62.
Russell W, Harrison RF, Smith N, Darzy K, Shalet S, Weetman AP, et al. Free triiodothyronine has a distinct circadian rhythm that is delayed but parallels thyrotropin levels. J Clin Endocrinol Metab. 2008; 93 (6): 2300-6.
Pedraza PE, Obregon MJ, Escobar-Morreale HF, del Rey FE, de Escobar GM. Mechanisms of adaptation to iodine defciency in rats: thyroid status is tissue specifc. Its relevance for man. Endocrinology. 2006; 147 (5): 2098-108.
Bianco AC, Salvatore D, Gereben B, Berry MJ, Larsen PR. Biochemistry, cellular and molecular biology, and physiological roles of the iodothyronine selenedeiodinases. Endocr Rev. 2002; 23 (1): 38-89.
Zaletel K, Gaberšček S. Hashimoto’s thyroiditis: from genes to the disease. Curr Genomics. 2011; 12 (8): 576-88.
Andersen S, Pedersen KM, Bruun NH, Laurberg P. Narrow individual variations in serum T3 and T4 in normal subjects: a clue to the understanding of subclinical thyroid disease. J Clin Endocrinol Metab. 2002; 87 (3): 1068-72.
Andersen S, Bruun NH, Pedersen KM, Laurberg P. Biologic variation is important for interpretation of thyroid function tests. Tyroid. 2003; 13 (11): 1069-78.
Völzke H, Caron P, Dahl L, de Castro JJ, Erlund I, Gaberšček S, et al. Ensuring effective prevention of iodine defciency disorders. Tyroid. 2016; 26 (2): 189-96.
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