Thyroid disorders epidemiology

Based on such evidence on iodine-induced disease in individual patients, it would be expected that an increase in population iodine intake would lead to an increase in the incidence and prevalence of certain thyroid disorders. To evaluate this in more detail, and to obtain information on the level of iodine intake where such an increase will take place, epidemiological studies are necessary. As shown in Table 47.1 there is evidence to suggest that a number of abnormalities may be more common when iodine intake becomes high. However, in general the evidence is less strong, compared with the evidence for less disease with eradication of iodine deficiency (Table 47.1), and the sum of burdens is lower (Figure 47.1). 

The monitoring program of iodine intake and thyroid diseases (DanThyr) was designed to secure optimal iodine nutrition of the Danish population, and also to improve knowledge on how to evaluate the iodine status of a population. Moreover, the design would give information on the epidemiology of thyroid disorders in areas with different levels of iodine intake, and the effects of an increase in iodine intake. An additional aim was to clarify the role of various environmental factors for the development of thyroid disease in the population, and in particular to study how these factors may interact with iodine intake. 

Iodine is essential for a normal thyroid function., Animal studies, epidemiological studies in man without direct measurement of iodine stores and in vitro studies on thyroid slices have demonstrated the importance of TITI variations in the etiology of some thyroid disorders. Direct assessment of TITI in vivo in man and most importantly its evolution in time is now possible by means of XRF. The major part of stable iodine in the gland represents mainly functional thyroid tissue, with some exceptions, such as in the case of contamination with iodinated drugs or radiological contrasts.. An excellent correlation between XRF measurements... 

Thilly CH, Swennen B, Bourdoux P, et al. 1993. The epidemiology of iodine-deficiency disorders in relation to goitrogenic factors and thyroid-stimulating-hormone regulation. Am J Clin Nutr 57(2 Suppl) 267S-270S. 

One of the first retrospective epidemiologic studies of teenage children demonstrated an association of soy consumption in early infancy and a higher prevalence of autoimmune thyroid diseases (Fort et al., 1990). This work was criticized, in part because children were often fed with soy formulas in order to prevent allergic disorders, known to be associated with autoimmune diseases (Chandra, 1997). 

Iodine Deficiency Disorders (IDD) are a major international public health problem (1). The effects of iodine deficiency occur at all ages, but are particularly important during the period of fetal development. The available epidemiological evidence has been complemented by experimental studies of fetal development in animal models. These have focussed particularly on fetal brain development because of its obvious importance Definite effects have been observed in a variety of animal models - the rat, the marmoset and the sheep. In addition studies of the mechanisms involved have been carried out which have revealed the importance of maternal thyroid function for fetal brain development. 

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