Physiological goiters

Physiological goiters are rare in the elderly in the developed world. An intervention is not needed in most patients if they are euthyroid. These patients should be reassured and prescribed a high iodine diet. Some patients present with symptoms of hypothyroidism. Thyroxine replacement is indicated in these patients, and goiter diminishes in size in 4-6 months. The starting dose of thyroxine in the... 

The many effects of lithium on thyroid physiology and on the hypothalamic-pituitary axis and their clinical impact (goiter, hypothyroidism, and hyperthyroidism) have been reviewed (620). Lithium has a variety of effects on the hypothalamic-pituitary-thyroid axis, but it predominantly inhibits the release of thyroid hormone. It can also block the action of thyroid stimulating hormone (TSH) and enhance the peripheral degradation of thyroxine (620). Most patients have enough thyroid reserve to remain euthyroid during treatment, although some initially have modest rises in serum TSH that normalize over time. 

On the other hand, excess iodine intake may also inhibit thyroid function, by either inhibition of iodide organification (Wolff-Charkoff effect) or inhibition of Tg proteolysis with reduction in hormone secretion, and may manifest itself either as a goiter, as hypothyroidism with/without goiter, or as hyperthyroidism (0.01-0.6% in populations on iodine prophylaxis), the outcome depending on the initial and current iodine status and current thyroid dysfunction (European Commission, 2002). The comparison of iodine intake and concentrations of serum Tg at various physiological or pathophysiological conditions is shown in Table 6.1. 

Iodine deficiency affects the socioeconomic development of an afflicted community in other ways than its important physiological manifestations, viz., goiter, hypothyroidism, cretinism, reproductive failure, and child mortality, among others. The socioeconomic retardation of the affected community occurs in two ways. People are mentally slower and less vigorous, so it is harder to educate and motivate them, and thus they are less productive in their work. Besides, iodine deficiency produces more handicapped individuals who depend on others for their care, which in turn diverts the community resources. Secondly, in most of the areas, agriculture is the most important economic activity, and domestic animals suffer from iodine deficiency in much the same way as people do. Therefore, domestic animals are smaller in size and produce less meat, eggs and wool. They also suffer from abortion and are often sterile. 

In humans, Murray and Pochin (1951) have confirmed that isotopic iodine from iodate is available to the thyroid when given per os, but the bioavailabifity was about 10% lower than that of iodide. Five milligrams of iodine weekly per os reduced goiter prevalence among iodine-deficient children equally well, whether given in the form of iodate or iodide tablets (Scrimshaw et al., 1953). However, this study does not prove exact bioequivalence of the two iodine compounds, since the iodine dose by far exceeded the physiological requirement, which might have obscured minor differences in bioequivalence. 

Several studies have clearly shown that the main causal factor for endemic goiter in Mali is the lack of iodine (Konatd, 1978 Soucko 1981 Soumano, 1976 Togola, 1978 Traord, 1990b). This notion rests on numerous epidemiological surveys and on the evaluation of iodine in water and foods. The level of iodine in the soil and in water and foods in Mali is too low to fulfill the physiological needs of humans and animals (Beilis et at, 1988a Konate, 1978 Soucko, 1981 Traord, 1990). 

Ermans A.M., Verelst J. 1980. Acute effects of supra-physiological doses of iodine in the human being management of non-toxic goiter. J.Mol.Med. 4 199-202. 

One would be led to conclude that raising the thyroidal iodine concentration by moderate iodide supplies is an essential factor not only for the prevention of goiter but also for a physiological treatment, at least in children and young adults. 

Iodine is present in thyroid hormones, T3 (triiodothyronine) and T4 (thyroxine). The discovery of these hormones by the American biochemist Kendall earned him the Nobel Prize in Physiology and Medicine in 1950. A lack of iodine causes goiter, a disease that formerly was common in populations remote from coastal areas. 

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