China iodine deficient areas

NEUROPSYCHOLOGICAL STUDIES IN IODINE DEFICIENCY AREAS IN CHINA... 

Wang Y.Y. et al. Improvement in hearing among otherwise normal school children in Iodine-Deficient areas of Guizhou, China, following use of iodized salt. Lancet 1985 518-528. 

Another major effect of fetal iodine deficiency is the condition of endemic cretinism. This condition, which occurs with an iodine intake of below 25 ug per day in contrast to a normal intake of 100-150 ug per day, is still widely prevalent, affecting for example up to 10 per cent of the populations living in severely iodine deficient areas in India, Indonesia and China. In its most common form, it is characterised by mental deficiency, deaf mutism and spastic diplegia, which is referred to as the "nervous" or neurological type in contrast to the less common "myxedematous" type characterised by hypothyroidism with dwarfism. 

In Europe, where the content of selenium in soil is generally low, serum selenium concentrations range from 50 to 110 ig/L, above the 10-20 iig/L and 25-35 xg/L observed in selenium-deficient areas in China and Zaire, respectively. However, no data are available on the selenium status of more rural populations living in iodine-deficient areas. Considering the low selenium content of European soils and the importance of local nutritional factors, this possibility certainly exists and should be taken into account in future epidemiological studies. 

Iodine is essential in the mammalian diet to produce the thyroid hormone thyroxine deficiency in humans causes goitre. Collectively, deficiencies of iodine, iron, zinc and vitamin A in humans are thought to be at least as widespread and debilitating as calorie deficiencies (Welch and Graham, 1999). The main source of iodine in soils is oceanic salts rather than parent rock, and so deficiency is most widespread in areas remote from the sea (Fuge, 1996). In principle deficiency is easily corrected with dairy supplements. However in practice this is not always feasible. Addition of iodate to irrigation water has successfully corrected widespread iodine deficiency in parts of China where the usual methods of supplementation had failed (Cao et al., 1994 Jiang et al 1997). However there is not much information on the behaviour of iodine in soil and water systems. 

Selenium deficiency has been associated with specific diseases in China and Africa Keshan and Kashin-Beck disease (KBD) in Tibet and China and myxedematous cretinism in Central Africa. Interestingly, in all these selenium-deficient areas iodine deficiency is also endemic. The specific impact of iodine deficiency on human health is described elsewhere in this book and will not be repeated here, with the exception of health conditions where the interaction of iodine and selenium may contribute to the pathogenesis of a specific disease. This chapter will deal with diseases where both iodine and selenium deficiency play a role in disease causation and particularly with KBD. 

In Tibet, both endemic goiter and KBD are important public health problems. KBD occurs in areas of Tibet where selenium deficiency is endemic. In Tibet, as in most regions of China where selenium deficiency is endemic, iodine deficiency is also endemic, but the converse is not... 

The greatest challenge for the government of China now is to reach the remaining 10% population that has no access to adequately iodized salt, to ensure that the brains of unborn children in these areas are protected from the devastating effects of iodine deficiency. 

This finding has been supported by evidence from Ecuador, Zaire and China and there is now no reasonable doubt about the relation between iodine deficiency and cretinism. It is this relationship on which more fundamental research can now be based in order to explore the mechanisms involved. It is likely that this new knowledge will be applicable over a wide area of brain physiology and brain function. 

The better known areas that are leached are the mountainous areas of the world. The most severely deficient soils are those of the European Alps, the Himalayas, the Andes, and the vast mountains of China. However, iodine deficiency is likely to occur to some extent in all elevated regions subject to glaciation and higher rainfall, with runoff into rivers. It has become clear that iodine deficiency also occurs in flooded river valleys, such as the Ganges in India, the Mekong in Vietnam, and the great river valleys of China. 

While deficiencies of vitamin A, iron and iodine are priority targets for the World Health Organization (WHO), deficiency of vitamins (section 11.6.3) and B (section 11.7.3) continues to be a major problem in large areas of Asia and Africa, and selenium deficiency (section 11.15.2.5) is a significant problem in large regions of China, and elsewhere. 

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