From the Department Human Nutrition, All India Institute of Medical Sciences, New Delhi 110029, India.

Reprint requests: Dr. Umesh Kapil, Additional Professor, Department of Human Nutrition, All India Institute of Medical Sciences, New Delhi 110 029, India
E-mail: ukapil@ernet.medinst.in

In India, the disorders resulting from iodine deficiency are present throughout the country. Out of 275 districts surveyed by various Government of India institutions and Central Goiter Survey Teams in 25 States and 4 Union Territories, 235 have been found to be endemic for Iodine Deficiency Disorders (IDD). In view of magnitude of the problem as well as considering the technical, administrative, financial and operational feasibility, the Government of India took a decision in 1984 to iodize all edible salt in the country, i.e., Universal Salt Iodization (USI). However, recently concerns have been expressed by some quarters in mass and electronic media about the use of iodized salt and the policy of Universal Salt Iodization in the country. A National Consultation was convened on 21st April 1999 to discuss the cumulative scientific and epidemiological evidence on "Benefits and Safety of Iodized Salt" in the prevention and control of IDD. The objective of the Consultation was to develop a National Consensus Document on Benefits and Safety of Iodized Salt based on hard scientific data.

The participants of the National Consultation included scientists of various Departments of the Government of India namely Indian Council of Medical Research, Indian Council of Agricultural Research, Ministry of Health and Family Welfare, Ministry of Human Resources Development, Department of Women and Child Development, National Institute of Health and Family Welfare, All India Institute of Hygiene and Public Health, Planning Commission and National Institute of Public Cooperation and Child Development. Representatives of professional organizations like Nutrition Foundation of India, the Nutrition Society of India, Indian Academy of Pediatrics, Indian Association of Preventive and Social Medicine, Indian Public Health Association, Thyroid Association of India, Endocrinology Society of India, Association of Physicians of India, etc. also participated. Program managers from Salt Department, International and Bilateral Agencies like United Nations Children’s Fund (UNICEF), United States Agency for International Development (USAID), World Bank, World Health Organization (WHO), Micronutrient Initiative and Cooperative for American Relief Everywhere (CARE) also participated.

The following recommendations were made in the National Consultation.

1. Based on scientific studies of iodine balance over a 24 hour period, a safe daily intake of iodine has been estimated to be between a minimum of 50 mcg and a maximum of 1000 mcg. A generally accepted desirable dietary iodine intake by an adult is 100-300 mcg/day.

2. Iodine has relatively wide margin of safety. Acute and chronic toxicity studies with sodium iodate have been carried out. Results of these long-term animal and human experiments in doses comparable to those that are used in prophylaxis, have failed to produce toxic signs. On the basis of toxicological studies it has been confirmed that potassium iodate is very safe at the level used in salt iodization. This has been also confirmed on the basis of worldwide experience of salt iodization programs.

3. The average daily intake of iodine in Japan has been reported to be 3000 micrograms, which is 20 times more than the RDA value of 150 mcg in India. Studies carried out in normal Japanese population have shown that they are biochemically and clinically eumetabolic inspite of the consumption of large amounts of iodine. The values for their thyroid hormone are not different from those in non-endemic areas of other countries indicating their adaptation to excess iodine intake. Existence of this type of adaptation has also been confirmed by animal experiments. There is little indica-tion that iodine in the amounts noted influences the prevalence of any of the thyroid diseases.

4. The average daily salt intake in India is 10 g. Consumption levels are within the 5-15 g/day range for children and adults. As per Government of India recommendations, the level of salt iodization (quantity of iodine added to salt) should provide a minimum of 150 mcg of iodine per day at the consumption level. From the average daily intake of 10 g iodine fortified salt, the estimated availability of iodine would be 150 mcg, of which about 30% is lost during cooking. The remaining 105 mcg is ingested and from this about 70% is absorbed by the body. This means approxi-mately only 73.5 mcg is absorbed per day from iodine fortified salt. This quantity when added to the iodine daily consumed through food will be broadly comparable to the daily physiological need of the body. Indeed urinary iodine excretion studies in the post iodization phase show that all over the India, the salt iodization is not more than 300 mcg per day. Thus, the level of salt iodization is totally safe in our country.

5. Since iodine, when ingested in large amounts, is easily excreted in the urine, iodine intake even at very high levels (milligram amounts) can be safe. It is documented scientifically that through adaptive mechanisms, normal people exposed to excess iodine remain euthyroid and free of goiter. It is not correct to attribute skin reactions such as rashes and acne to iodized salt. Physiological levels of iodine intake do not cause "Iodism". For example, among 20,000 children in the USA suffering from allergy during the period 1935-1974, not a single case was reported of allergic hypersensitivity to iodine in food. Following publication in Annals of Allergy of a request for notification of allergy to iodine, not a single report was recorded between 1974 and 1980. However, high intakes of dietary iodine may induce hypothyroidism in autoimmune thyroid diseases and may inhibit the effects of thionamide drugs. Iodine-induced hyperthyroidism is an adverse effect, which may occur primarily in older people where severely iodine deficient populations increase their iodine intake, even when the total amount is within the usually accepted range of 100-200 mcg/day. Epidemiologically iodine-induced hyperthyroidism represents a transient increase in the incidence of hyper-thyroidism, which disappears, in due course with the correction of iodine deficiency. From a public health point of view, the benefits of correcting iodine deficiency through universal salt iodization greatly outweigh the risk of iodine-induced hyperthyroidism.

6. The daily iodine intake of upto 1 mg (1000 mcg) appears to be entirely safe. Iodization of salt at a level that assures an intake of 150-300 mcg/day keeps iodine intakes well within daily physiological needs for all populations, irrespective of their iodine status. In India, daily consumption of 10 g of salt containing 15 parts per million of iodine would add a maximum of only 150 mcg of iodine. Thus, the likelihood of exceeding an iodine intake of 1 mg/day from iodized salt is negligible.