IDD as a public health problem.
|Publication:||Name: Indian Journal of Medical Research Publisher: Indian Council of Medical Research Audience: Academic Format: Magazine/Journal Subject: Biological sciences; Health Copyright: COPYRIGHT 2008 Indian Council of Medical Research ISSN: 0971-5916|
|Issue:||Date: Nov, 2008 Source Volume: 128 Source Issue: 5|
|Product:||Product Code: 8000120 Public Health Care; 9005200 Health Programs-Total Govt; 9105200 Health Programs NAICS Code: 62 Health Care and Social Assistance; 923 Administration of Human Resource Programs; 92312 Administration of Public Health Programs|
Iodine deficiency disorders (IDD) are a major global pubic health
problem. As per the estimates of WHO in 1999, 130 out of the 191 Member
States are affected by IDD. Of the remaining 61 countries, IDD has
either been eliminated or is not known be present in 20 countries. There
are insufficient data from the remaining 41 countries. Most of the
affected regions of the globe, are in Africa (44 countries out of 46)
and South East Asia (9 countries out of 10) (1).
Cause of IDD is deficiency of iodine in the soil. In the regions where there are repeated flooding and glaciations, the iodine gets leached out of the upper crust of the earth leading to environmental iodine deficiency. The vegetation as well as grass grown on such soil leads to iodine deficiency in food consumed by humans and animals. To correct this, most of the affected countries have taken different measures to supply iodine to the population. These include iodized salt, iodized oil injection, iodized oil capsules (oral), and iodization of drinking water (1). Some of these are short-term measures but the best long term method is use of iodized salt, as salt is taken in fixed amount by everybody, every day round the year and by all age groups. Thus salt is used as a vehicle for supply of iodine in majority of the countries (Universal salt iodization programme).
WHO/UNICEF/ICCIDD have jointly recommended outcome and process indicators to track the progress of IDD elimination (2). Of the several indicators recommended in developing countries, goitre grading and urinary iodine levels are the most feasible to use as outcome indicators while iodine content of salt is the best as a process indicator. The WHO/UNICEF/ICCIDD recommendations provide separate cut off points for these indicators to assess the severity of IDD as well as for tracking IDD elimination programmes. Recent surveys carried out in Bhutan, Nepal, Thailand as well as seven States in India provide evidence that suggests that it is essential to view the results of these three indicators in totality rather than in isolation to make proper assessment of progress of IDD elimination programme (3).
Chandra et al (4) in this issue have studied 1286 school children between the age group of 6 to 12 yr in Imphal east, north-east India. Urine samples (n=160) were analysed amongst the study population, 40 from each locality for Iodine and thiocyanate levels. Goitre rates were high in spite of adequate iodine intake as judged by iodine content of salt and urinary iodine excretion pattern in the population studied. Authors implicate the intake of thiocyanate in proportion to iodine as a responsible factor for goitres seen. However, the I/SCN ratio was way above 7 in 95 per cent of the samples analysed only 5 per cent showed this ratio less than 7 and none below 3, a critical level at which goitre develops.
WHO, UNICEF, ICCIDD (2) had recommended three criteria for elimination of IDD, goitre rates less than 5 per cent, median urinary iodine levels above 100 [micro]g/l, and 90 per cent of households having adequate iodine intake. Recent studies in 3 countries and 7 States of India have shown that goitre rates are little on higher side with median urinary iodine excretion above 100 [micro]g/l but only 50 per cent of household taking adequate amount of iodine (2). The higher goitre rates in these studies were attributed to not consuming adequate amount of iodine by the population, however, in the study by Chandra et al (4) intake of iodine was satisfactory in more than 90 per cent of house holds. This naturally brings out the question of what is causing goitre in this area.
Goitrogenic substances taken in the diet interfere with proper utilization of available iodine by the thyroid gland. There are two types of goitrogens described, one type which interferes with iodine uptake by the thyroid gland and include thiocyanate and perchlorate, while the other type are substances which inhibits the thyroid organic binding and coupling i.e., formation of thyroid hormones (5). Both types of goitrogens will lead to less formation of thyroxine thereby increasing circulating levels of thyroid stimulating hormone (TSH) which is responsible for thyroid enlargement i.e., goitre.
The results of the above study (4) do not support implication of thiocyanate (as shown by I/SCN ratios in urine), while possibility of other goitrogens which interfere with organification and coupling, needs further investigation.
Before implicating the role of goitrogenes, it is essential to undertake further investigations in the population to resolve the public health problem. The following investigations need to be done: (i) Circulating levels of T4 and TSH, (ii) [sup.131] I uptake, (iii) perchlorate discharge test, (iv) plasma inorganic iodide concentration, and (v) mono iodotyrosine (MIT), di iodotyrosine (DIT) levels in circulation.
Such investigations should throw more light on possible role of goitrogens in the population. The findings of Chandra et al (4) have raised some queries/doubts. Are there factor/factors other than iodine deficiency which cause goitre in the population? Implication of goitrogens need further investigations as mentioned above. Other possibility is genetic defects in the population which also needs a systematic study amongst the population in Imphal.
(2.) WHO/UNICEF/ICCIDD. Indicators for assessing iodine deficiency disorders and their control through salt iodization. WHO/NUT/94.6,1994.
(3.) Karmarkar MG, Pandav CS. Interpretation of indicators of iodine deficiency disorders: Recent experiences. Natl Med J India 1999; 12 : 113-7.
(4.) Chandra AK, Singh LH, Debnath A, Tripathy S, Khanam J. Dietary supplies of iodine & thiocyanate in the aetiology of endemic goitre in Imphal East of Manipur, north east India. Indian J Med Res 2008; 128 : 597-601.
(5.) Gaitan E. Goitrogens in food and water. Annu Rev Nutr 1990; 10 : 21-39.
Centre for Community Medicine
All India Institute of Medical Sciences
Ansari Nagar, New Delhi 110 029, India
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