Iodine Deficiency: Background, Pathophysiology, Epidemiology
Iodine deficiency disorders (IDD) is now a global health problem. Nearly 486 million people are at risk of iodine deficiency disorders and 176 million have goiters in the South-East Asia Region. Most affected areas are in the northern and central districts. The overall prevalence as measured in a nationwide survey (IPHN) in 1981-82 was. estimated around 10.5%. But a survey conducted in 1993 jointly by the IPHN, INFS, UNICEF and the International Council for Control of Iodine Deficiency Disorders (ICCIDD) put the prevalence rate of visible goiter at 47.1% and the at-risk population at 68.9%. With the introduction of the Universal Salt Iodization Programme, the situation seems to have improved substantially. A repeat survey in 1999 has found a total goiter rate of 17.8% and the biochemical deficient at-risk population to be 43.1%. The prevalence of cretinism, however, has reduced from 0.5% to 0.4%. Though goiter is the most obvious and familiar feature of iodine deficiency, the effects of the same on growth and development are now denoted by the terms of iodine deficiency disorders (IDD). In the past goiter received less attention for its few known complications and were treated for cosmetic purposes only. Recent studies on IDD indicate a wide range of disorders including hypothyroidism, deaf-mutism, cretinism, physical and mental retardation, and dwarfism. In recent years due to the use of iodized salt the prevalence of IDD has improved in the SEAR countries and it appears that they are moving closer to the Regional goal of less than 10% prevalence of endemic goiter by the year 2000.
Goitrogens. These are chemical substances usually found in the inedible portions of certain plants. When located in the edible portions. they are liberated and being active interfere with iodine utilization by the thyroid gland. Cyanogenic glucosides, by hydrolysis, liberate large quantities of cyanide which itself is toxic. It forms a metabolite thiocyanate which is a goitrogen. Food of the Brassica family, namely cabbage and cauliflower. as well as cassava consumed in many African countries are potential goitrogens.
Lathyrism. Though not a deficiency disease. it deserves to be mentioned here, as a significant number of cases are still found in the northern districts of Bangladesh. It is a neurologic disease seen in those who have consumed large amounts (over 30% of the total diet) of Lathyrus sativus (khesari dal) over a prolonged period of time (2-6 months) with no diversification in the consumed food items. Though several toxins have been reported, beta-oxalyl-amino-alanine (BOAA) is principally responsible for causing lathyrism.
Prevention of lathyrism. As long as substitute crops are not provided, it will be difficult to implement a ban on the production of this crop. which takes less effort to grow and the yield of which is plenty. Ironically the protein content of khesari dal is also high and its taste is acceptable to all Bangladeshis. The toxin can be effectively removed if the pulse is soaked overnight preferably in warm water and the water is discarded before the preparation of food items. The toxin being water-soluble is thus removed. Parboiling is recommended as a large scale measure. Selective cultivation of strains containing lower levels of the toxin is another helpful measure. Here is one situation where public health education has a considerable role to play.
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Fluorosis. Excessive amounts of fluorine (3- 5mg/L) in drinking water may lead to fluorosis. Frank cases of scurvy, pellagra, beriberi are diseases of the past. However, it is possible to have a relative deficiency of the nutrients causing these diseases in all cases of severe food deprivation taking place over a prolonged period of time. This could probably explain the occurrence of sporadic cases of rickets in children seen in a land of plentiful sunshine. Angular stomatitis blamed to be due to deficiency