Changes

===Iodine Deficiency Disorders (IDD)===

===Iodine Deficiency Disorders (IDD)===

[[File:UNN_Medical_Geology_Fig_6.png|thumb|400px|{{figure number|6}}Man with goiter<ref>Fuge, R., 2010, Soils and Iodine Deficiency. In: Selinus, O., Alloway, B., Centeno, J.A., Finkelman, R.B., Fuge, R., Lindh, U. and Smedley, P., eds., Essentials of Medical Geology. Elsevier, Amsterdam: 417-433.</ref>]]

[[File:UNN_Medical_Geology_Fig_6.png|thumb|400px|{{figure number|6}}Man with goiter<ref>Fuge, R., 2010, Soils and iodine deficiency, ''in'' O. Selinus, B. Alloway, J. A. Centeno, R. B. Finkelman, R. Fuge, U. Lindh, and P. Smedley, eds., Essentials of medical geology: Amsterdam, Elsevier, p. 417-433.</ref>]]

Iodine is very important for the proper functioning of the human body. In all mammals, it is needed for the efficient functioning of the adult in trace amounts in the order of 0.0004 wt%.<ref name=Dvies /> This quantity is maintained as a result of small intake of iodine from drinking water and various forms of foodstuffs throughout the lifetime of the mammal.

Iodine is very important for the proper functioning of the human body. In all mammals, it is needed for the efficient functioning of the adult in trace amounts in the order of 0.0004 wt%.<ref name=Dvies /> This quantity is maintained as a result of small intake of iodine from drinking water and various forms of foodstuffs throughout the lifetime of the mammal.

To curtail IDD, salt iodization programme has been introduced, not only in this region but in all African countries. However, this project has not yielded maximum results due to the counteracting effect of goitrogens in the African diet. Goitrogenic effect comes from certain vegetables such as brassica. It proceeds by depressing the formation of thyroid hormone leading to increased secretion of thyroid stimulating hormone (TSH). The thyroid gland responds to this by enlarging itself as a compensating mechanism leading to the development of goiter ([[:File:UNN_Medical_Geology_Fig_6.png|Figure 6]]).<ref name=Dvies /> Another substance with goitrogenous effect is thiocyanate which is present in cassava consumed in many African countries. It inhibits the entrance of iodine into the thyroid gland.<ref name=Dvies />

To curtail IDD, salt iodization programme has been introduced, not only in this region but in all African countries. However, this project has not yielded maximum results due to the counteracting effect of goitrogens in the African diet. Goitrogenic effect comes from certain vegetables such as brassica. It proceeds by depressing the formation of thyroid hormone leading to increased secretion of thyroid stimulating hormone (TSH). The thyroid gland responds to this by enlarging itself as a compensating mechanism leading to the development of goiter ([[:File:UNN_Medical_Geology_Fig_6.png|Figure 6]]).<ref name=Dvies /> Another substance with goitrogenous effect is thiocyanate which is present in cassava consumed in many African countries. It inhibits the entrance of iodine into the thyroid gland.<ref name=Dvies />

In China, about 425 million people are at risk of IDD. In iodine deficiency areas, a serious shortage of iodine intake by pregnant women would affect the development of the nervous system of the fetus and newborn infants would likely suffer from cretinism and related health problems.<ref>Zheng, B., B. Wang, and R. B. Finkelman, 2010. Medical Geology in China: Then and Now. In: Selinus, O., Finkelman, R.B. and Centeno, J.A., (eds), Medical Geology: A Regional Synthesis, 303–319.</ref> Endemic cretinism prevailed in Chinese regions with acute iodine shortage. Analysis showed that places with iodine threshold of 25μg suffer from endemic cretinism whereas places with only goiter usually have iodine threshold of 50 μg. This triggered off a research into the relationship between goiter and cretinism in 25 provinces on 750,000 persons. The research showed that goiter had an average prevalence rate of 24.92% while cretinism had an average prevalence rate of 3.15% (Zheng et al, 2010). Fortunately, inhalation of iodine volatized from coal has contributed to increased reduction in the goiter cases.

In China, about 425 million people are at risk of IDD. In iodine deficiency areas, a serious shortage of iodine intake by pregnant women would affect the development of the nervous system of the fetus and newborn infants would likely suffer from cretinism and related health problems.<ref name=Zheng2010>Zheng, B., B. Wang, and R. B. Finkelman, 2010, Medical geology in China: Then and now, ''in'' O. Selinus, R. B. Finkelman, and J. A. Centeno, eds., Medical geology: A regional synthesis, p. 303–319.</ref> Endemic cretinism prevailed in Chinese regions with acute iodine shortage. Analysis showed that places with iodine threshold of 25μg suffer from endemic cretinism whereas places with only goiter usually have iodine threshold of 50 μg. This triggered off a research into the relationship between goiter and cretinism in 25 provinces on 750,000 persons. The research showed that goiter had an average prevalence rate of 24.92% while cretinism had an average prevalence rate of 3.15%.<ref name=Zheng2010 /> Fortunately, inhalation of iodine volatized from coal has contributed to increased reduction in the goiter cases.

===Health effects resulting from the deficiency and excessiveness of selenium===

===Health effects resulting from the deficiency and excessiveness of selenium===