Iodine deficiency disorders (IDD) is still one of public health nutrition problems in many countries, including Indonesia. Through various efforts the IDD prevalence is reducing, but still unsatisfactory.

It is widely accepted that iodine deficiency is caused mainly by low availability of iodine in the soil. However, role of some other substances is of attentions for the last decade, including goitrogenic substances. Other micronutrients might play important role. The paper is concentrating on the relationship of selenium and iodine deficiency.

Selenium is one of essential micronutrients. The requirement is quite low and (theoretically) easy to be toxic in higher doses. It can be found in seafood, organ and small amount in plants. It is consumed as inorganic selenium, selenomethio-nine and selenocycteine. The absorption is passive in a high proportion, hence it does not play in homeostasis of selenium.

Through complex protein-related transport and transfers, the main role of selenium is as selenoprotein in various forms, i.e.: (i) Gluthation peroxidase (GPx); (ii) Thioredoxin reductase; (iii) Iodothyronine deiodinase; (iv) Selenoprotein P; (v) Selenoprotein W; and (vi) Selenophosphate synthetase.

The interrelationship between iodine and selenium in the soil need to be clarified. Although the issue is still interesting to search, most researchers agree that selenium plays important role in iodine metabolism through the following mechanism:(i) role of iodothyronie deiodinase which catalyses the conversion of T4 to T3 (and T3 to T2) as the most important path of thyroid hormon metabolism; (ii) role of GPx as main antioxidant which protect cell membrane (of also thyroid gland) to process thyroid metabolism; moreover GPx acts as balancer of availability of T4 and T3, especially in the important organs such as brain and heart, and very specially in foetus; (iii) estrogen sulfotransferase which control development estrogen to prevent excess which is potential to depress thyroid function. Role of interaction of selenium deficiency and goitrogenic overload is also found to be very important. Those all brings us to think of selenium-iodine balance in relation to the development of thyroid hormone.

The above feature of selenium implies to include selenium consideration in all IDD policy. Including selenium assess-ment in the soil in IDD endemic areas, with high priority for areas where iodine content of soil is not seriously low or IDD prevalence is fail to reduce by iodine supplementation only.

When both iodine and selenium deficiency is found or assumed, mixed iodine and selenium supplementation should be considered in a gradual doses based on the severity of the problem.

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