Mild iodine deficiency

The complexity of the interaction between iodine intake and autoimmune thyroid disease has been highlighted by reports of evidence that iodide (compared with thyroxine) induces thyroid autoimmunity in patients with endemic (iodine deficient) goiter (43), while in those with pre-existing thyroid autoimmunity, evidenced by the presence of antithyroid (thyroid peroxidase) antibodies, administration of iodine in an area of mild iodine deficiency led to subclinical or overt hypothyroidism (44). 

Reinhardt W, Luster M, Rudorff KH, Heckmann C, Petrasch S, Lederbogen S, Haase R, Sailer B, Reiners C, Reinwein D, Mann K. Effect of small doses of iodine on thyroid function in patients with Hashimoto s thyroiditis residing in an area of mild iodine deficiency. Eur J Endocrinol 1998 139(l) 23-8. 

ViTn P, Martino E, Aghini-Lombardi E, et al. (1994) Thyroid volume measurement by ultrasound in children as a tool for the assessment of mild iodine deficiency. J Clin Endocrinol Metab 79 600-603. 

When iodine requirements are not met, TH synthesis is reduced, resulting in enlargement of the thyroid gland to compensate for this reduction. In adults, mild iodine deficiency (ID) is associated with nontoxic nodular goiter and, less often, with toxic nodular goiter, due to increases in the constitutive (thyrotropin-independent) growth and functional potential of some clones of thyroid cells. In pregnancy, this can result in fetal neurodevelopmental deficits and mental retardation. 

Mild iodine deficiency (urinary excretion 50-99pg iodine/g creatinine) 64 (42%) 219(34%) 283 (36%)... 

In spite of a mean UI within the range of iodine sufficiency, 36% of the study subjects had mild iodine deficiency with UIs between 50 and 99pg/g. Moreover, 21% of the study population had moderate-to-severe iodine deficiency [UI < 50pg/l (pg/g)]. It should, therefore, be discussed urgently whether it is acceptable to label a population as iodine sufficient according to the WHO criteria eventhough up to 20% of the population can be severely iodine deficient and 36% can be mildly iodine deficient. 

A similar finding of more subclinical hypothyroidism with abundant iodine intake compared with mild iodine deficiency was reported in nursing home residents living in Hungary (Szabolcs et al, 1997). In China, people having excessive iodine intake from a combination of high groundwater... 

In Denmark, we studied the incidence of overt hypothyroidism before the Danish iodine program in two areas with a small difference in iodine intake caused by different iodine contents of groundwater. The population hv-ing in the area with only mild iodine deficiency had a considerably higher incidence of overt hypothyroidism than the population with moderate iodine deficiency, whereas the lower iodine intake was associated with more hyperthyroidism (Figure 47.5) (Billow Pedersen et aL, 2002). Subtyping of disease revealed that the difference in hypothyroidism was caused by 50% more cases of spontaneous autoimmune hypothyroidism in the area with the highest iodine intake (Carld et ai, 2006). 

Even mild iodine deficiency results in suboptimal psychomotor performance in childhood. 

Yavuz et al. (2004) investigated the relationship between Fe status and thyroid hormones in adolescents living in an iodine-deficient area. The purpose was to evaluate the effect of Fe status on the thyroid hormone profile in adolescents living in a mildly iodine-deficient area in Turkey. 

In populations with even mild iodine deficiency, an increased goiter rate can be seen. Delange et al. (1997) have measured thyroid volume and urinary iodine excretion in 5709 children aged 7—15 years in different sites in 12 European countries. All ultrasound examinations and urinary iodine assays were performed by the same investigators. An inverse relationship was found (Figure 55.3). 

In summary, both intra- and extrathyroidal mechanisms are involved in the adaptation of the rat to mild iodine deficiency the former are autoregulatory and very effective in avoiding T3 deficiency in most tissues and the latter occur in tissues in which type 2 iodothyronine deiodinase (D2) plays an important role for the local generation of T3. In mild ID, hypothyroidism, as inferred from the concentrations ofT3, is avoided in all tissues studied. The question remains as to whether or not tissues with elevated T3 concentrations may actually be hyperthyroid. As far as we know, this question cannot yet be answered because tissue-specific thyroid hormone-sensitive biological endpoints have not been measured in mildly iodine-deficient rats with increased circulating T3. 

The study was carried out in the inner valleys of western Asturias (a northern Spanish region). This is an isolated mountainous area, with an autarkic farmers population and long-standing IDD. Ten years after the introduction of an iodized-salt diet, infantile endemic goiter has been reduced from 63% to a mild iodine deficiency of 16.4% (Enguix et al., 1995). One hundred and eleven consecutive women who asked for antenatal assessment at the local medical center of the Spanish National System gave their consent to Paloma Sanchez Martinez in order to participate in the study. The Ethics Committee gave its approval to the study. 

Iodine supplementation probably begins late in many pregnant women (at the first prenatal care visit), missing the critical period of fetal brain development. However, there is no clinical data so far that supports the effect of iodine supplementation on neural development in pregnant women from mild iodine-deficient areas in both the short- and long-term. These data indicate that continued efforts for USI remain a public health priority. 

In the same group of women, the incidence of hyperthyroidism was 1.3 cases/1000/year and of hypothyroidism 1.0 cases/1000/year. These data can be compared to data from studies from Denmark (Laurberg et ai, 2006), which show that only a small difference in iodine intake is associated with a large difference in incidence of overt hyper- and hypothyroidism. Thus, the incidence rate of hyperthyroidism for women in a region with moderate iodine deficiency (urinary iodine 45 lig/1) was higher than in a region with mild iodine deficiency (urinary iodine 61pg/l) 1.5 cases/1000/year compared to 1.0 cases/1000/year. In... 

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