Dietary iodine deficiency

Worldwide, the most common thyroid disorder is hypothyroidism resulting from dietary iodine deficiency. In iodine-replete areas of the world, most thyroid disorders are the result of autoimmune disease. The symptoms manifested in hypothyroid and hyperthyroid states are largely independent of any underlying disorder of the thyroid gland itself they are a function of the degree of hormone deficiency or excess. 

Patients with multinodular goiter and thyroid autonomy, especially if they are elderly and/or live in areas of dietary iodine deficiency... 

Prophylaxis is generally not necessary Patients at risk should be closely monitored by endocrinologists after iodinated contrast medium injection In selected high-risk patients prophylactic treatment may be given by an endocrinologist this is more relevant in areas of dietary iodine deficiency Intravenous cholangiographic contrast media should not be given to patients at risk... 

Thyroid disorders may be divided into over- and underproduction of the thyroid hormones. These may be caused by thyroid gland disorders or disorders of the pituitary gland (TSH production) or hypothalamus (thyrotropin-releasing hormone release). Thyroid hormone deficiency in infancy may cause mental retardation if it is not corrected immediately after birth. For this reason, many states require thyroid function tests in all newborns. In adults, thyroid deficiency may be caused by Hashimoto s thyroiditis, an immune disorder, or dietary iodine deficiency, in which case it is called simple goiter. The term "myxedema" has been used to refer to hypothyroidism of whatever cause. Myxedemas may... 

The thyroid gland is the only part of the body that absorbs iodine. Thyroid cells use iodine to produce thyroid hormones, which regulate metabolism. Low levels of iodine in the diet can lead to thyroid-hormone deficiencies and goiters, which are enlarged thyroid glands. In serious cases, low levels of thyroid hormones can cause birth defects and brain damage. In the United States, potassium iodide is added to most table salt to protect against dietary iodine deficiency. Even small amounts of added iodine can prevent iodine-deficiency disorders. However, there are parts of the world in which iodine deficiency is still prevalent. 

Iodine is an essential component of thyroid hormones, and iodine deficiency can lead to severe hypothyroidism. On the other hand, excessive iodine intake also results in thyroid dysfunction in certain persons. Coindent described the first case of iodine-induced hyperthyroidism in 1821 (Fradkin and Wolff, 1983), and Hurxthal (1945) reported the first case of iodine-induced hypothyroidism. Ingestion of iodine-rich foods, such as seaweed, can cause hyperthyroidism, and the incidence of hyperthyroidism showed an increase in regions of dietary iodine deficiency after prophylactic iodization of bread or salt. Iodine-containing pharmaceuticals, such as povidone-iodine (PVP-I), radiographic contrast media and amiodarone, are a major source of excessive iodine intake (Wolff, 1969 Fradkin and Wolff, 1983 Markou et aL, 2001 Roti and degli Uberti, 2001). 

A similar situation, such as subclinical hypothyroidism, could arise with iodine deficiency causing maternal hypothyroxinemia or frank hypothyroidism. Dietary iodine deficiency is potentially the most likely cause therefore, it would be prudent to screen for iodine deficiency or optimize dietary iodine intake. 

Iodine deficiency is the primary preventable cause of brain damage and psychomotor development retardation, and hence is a global public health issue. According to the United Nations International Council for the Control of Iodine Deficiency Disorders (ICCIDD), approximately half of the worlds population presented some degree of dietary iodine deficiency in 2002 (International Council for the Control of Iodine Deficiency Disorders, 2002). 

Dietary iodine deficiency also results ftom other practices that are typical of modem life. A large portion of the salt currently consumed comes ftom industrialized food products that do not contain iodine, because of the instability that it causes in industrialized foods (Brasil/ Ministerio da Saude/ANVISA, 2003). Iodine ftom meat and milk has also been reduced, due to changes in livestock raising and feeding methods (Health Eating Club, 2003). 

Iodine deficiency represents a major pubfic health problem in many countries in the Asia Pacific region. The World Health Organization (WHO) estimates that there are close to 1 billion people living in the southeast Asian and western Pacific regions, out of approximately 2 billion worldwide, who have urinary iodine excretion (UIE) less than the minimum level of 100 j,g/l (Table 127.1). As a consequence, it is speculated that mental and physical growth will be impeded in hundreds of millions of iodine-deficient children within this part of the world and they will not realize their full genetic potential because of dietary iodine deficiency. 

Majem, L., Tresserras, R., Canela, J., and Salleras, L. (1988). Dietary iodine deficiency and breast cancer mortality An ecological study. Int. J. Epidemiol. 17,686-687. 

Table A. Histological data at lAO days gestation of brain regions from fetal sheep during severe dietary iodine deficiency (mean values). ...

Cragg, B.G., Marshall, J., Wellby, M.L. and Hetzel, B.S. Retarded fetal brain development resulting from severe dietary iodine deficiency in sheep. Neuropath, appl. Neurobiology 8 303-313 (1982). 

When dealing with starvation, individual nutritional factors tend not to be assessed. Yet lack of specific micronutrients could very well affect cognition. Certainly, dietary iodine deficiency is implicated in endemic cretinism with marked, often irreversible, mental retardation, deaf-mutism, and motor defects. While endemic goiter afflicts 200 million people worldwide, only in regions of severe deficiency are infants born cretinous. 

It is usually measured by radioimmunoassay. Low serum levels are found in hypothyroidism while high levels occur in hyperthyroidism. Occasionally a raised serum T3 level may be found in the presence of a normal level of serum thyroxine (T3 toxicosis ). This can occur when there is dietary iodine deficiency. It may also represent an early stage in the development of full thyrotoxicosis. 

Kelp tablets—Just about every brand of these tablets contains an amount of iodine equal to the U.S. RD/ s for adults (150 meg per day) in each tablet. It is not wise to exceed this amount because people who have tendencies to develop goiter are extra susceptible to iodine toxicity. Those who have suffered from dietary iodine deficiency may have thyroid glands which have adapted to low intakes of the mineral by becoming very efficient in the production of thyroid hormones. Thus, their glands may overproduce these hormones when the dietary level of iodine is raised. 

A number of dietary deficiencies may increase the risk of deleterious cyanide effects. Iodine deficiency is involved in the etiology of such thyroid disorders as goiter and cretinism. These disorders may be exacerbated by excess exposure to cyanide (Delange and Ermans 1971 Ermans et al. 1972). Protein deficiencies and vitamin B12, riboflavin and other vitamins and elemental deficiencies may subject people... 

A normal rate of thyroid hormone synthesis depends on an adequate dietary intake of iodine. Iodine is naturally present in water and soil, although some soils contain very low amounts. As a result, seafood is a more reliable source of iodine than crop plants. Approximately 1.6 billion people in more than 100 countries live in areas where natural sources of dietary iodine intake are marginal or insufficient. A minimum of 60 j.g of elemental iodine is required each day for thyroid hormone synthesis, and at least 100 j.g/day is required to eliminate thyroid follicular cell hyperplasia and thyroid enlargement (i.e., iodine deficiency goiter). 

Juvenile or adult patients with primary hypothyroidism (as indicated by low serum free T4 and high serum TSH concentrations) are usually treated with thyroxine with the aim of relieving symptoms and reducing the serum TSH concentration into the normal reference range. If the primary hypothyroidism is the result of iodine deficiency, then gradually increasing dietary iodine supplementation may also be instituted in addition to the thyroxine replacement therapy. Iodine supplementation alone may lead to the development of acute hyperthyroidism. 

Or, to put it more positively, by adding small amounts of iodide to common salt we can prevent the medical condition known technically as cretinism, a life-long affliction of innately low intelligence caused by iodine deficiency, and which causes permanent brain damage. Nor does this simple dietary requirement cost very much. To provide all 6.5 billion people on the planet with the 70 micrograms of iodine they need every day would require only 166 tonnes of iodine per year, which represent a mere 2% of the iodine the world produces annually. This is an amount that chemists could easily extract from seaweed, making it a sustainable resource, and indeed this was once the way they obtained this remarkable element. 

Some degree of iodine dietary deficiency was estimated to affect 750 million people in the developing world in 1990 with around 10 million were suffering from stunted growth and mental retardation. In 1993 the WHO published a database of iodine deficiency based on the number of goitre victims in 121 countries where the element was in short supply. This shortage was most prevalent where soils have suffered repeated glaciations or heavy rainfall which had removed most of the iodide that may once have been present, because this is a particularly soluble material and so easily washed away. Those most at risk lived in India and China. 

Goiter is the human pathology of hyperplasia of the thyroid gland induced by the deficiency of dietary iodine. The disease is localized in those regions where soils are low in iodine or where seafood is not consumed. Fortification of fable salt with sodium iodide, where applied, has practically eradicated this disease. Unfortunately, many regions of the world do not practice this public health policy. 

For some trace elements, continued suboptimal dietary intake— in the presence of physiological, nutritional, or other metabolic stress— may eventually have a detrimental effect. Then additional dietary supplementation may have a health restorative effect. Such effects are most clearly demonstrated in experimental animals. Examples include the effects of boron in the presence of vitamin D depletion, or the need for increased vanadium when there is either an experimentally induced deficient or excess supply of dietary iodine. ... 

Relatively few studies have examined environmental influences on the development of autoantibodies. A complex relation is seen between dietary iodine and prevalence of antithyroid antibodies, with increased prevalence reported in relation to iodine deficiency and to excess intake. This issue is discussed in greater detail in section 8.10 on iodine. 

Not all the effects of dietary intake of flavonoids are positive. The excessive consumption of soybean and its products has been considered goitrogenic in humans and animals. Several researchers have reported induction of goitre in iodine-deficient rats maintained on a soybean diet [125, 126, 127], In some cases, the extreme intake of soybean has been correlated with cancer. Thus, Kimura et al reported the induction of thyroid carcinoma in rats fed on defatted soybean deficient in iodine by up to 40% [128],... 

Lack ofiodine leads to iodine deficiency disorders (IDD), while excessive iodine dietary intake can result in pathological problems, namely goitrogenic effect (Underwood, 1971 WHO, 1996). Low iodine intake resulting in IDD is recognized as a global concern, while excessive iodine intake is not so frequent. For most people it is unlikely that they will exceed the upper level of iodine intake, which is given in Table 2.1 (FAO/WHO, 2006), from normal foods and supplements. 

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