It is interesting especially as iodine deficiency is being seen again in the UK and Europe. It is likely that intensive agriculture is contributing to the depletion of soils.
A lively discussion followed after the revelation that, in the Red Sea areas of Sudan, aid initiatives can in fact over-supplement diet by Iodising everything in the food, from salt to cooking oil. Surprisingly, few of the local population include fish in their diet. Excess Iodine can produce life-threatening effects; the beneficial dosage is very low indeed (one teaspoonful is a lifetime dose but needs to be administered every day) and having a narrow range, which differs during the course of life. Mothers-to-be need a higher dosage than other adults, starting from the 3rd month of pregnancy for maximum protection of the fetal brain.
The external sign of Iodine Deficiency, an enlarged goitre, is obvious but not the way that needs are measured, which is by urine tests. Debate continues as to the difference between free Iodine or rather its salts, and Iodine naturally bound in food such as fish.