Prevalence of Goiter precipitated by iodine deficiency in many parts of the world was the driving force behind compulsory iodization of this vital food ingredient universally. As is well known iodine is a constituent of the thyroid hormones, secreted by the Thyroid gland and naturally insufficient intake of this trace mineral can precipitate many metabolic abnormalities besides enlargement of the gland itself. Triodothyronine, (T3) and Thyroxine(T4) are synthesized in the body by incorporating 3 and 4 molecules of iodine respectively into the precursor and the concentration of these hormones influences the metabolic rate in the body. Hypothyroidism, hyperthyroidism and autoimmune thyroditis are all manifestations of low or high iodine intake in the humans. It is some what difficult to precisely conclude whether one is having iodine deficiency or not and as any deficiency can have serious consequence on the health of human beings, especially children, universal iodization of salt is being promoted in almost all countries, hoping that thyroid related health disorders are totally eliminated.
Global statistics, assuming they are reliable tell a scary story regarding the prevalence of iodine deficiency in this world. 1.6 billion people including 50 million young children and 280 million school going children are supposed to be affected by iodine deficiency of different degree. As thyroid gland has a strong influence in the development of brain the impact of iodine deficiency, especially among children, if not treated can be mind boggling. This is the reason why universal iodization is considered the most effective health related intervention in all countries. Generally a daily intake of 150-200 mcg (microgram) of iodine is considered optimum for an adult while pregnant women and breast feeding mothers may need some what higher levels of intake. It is further claimed that excess iodine intake, even as high as 10 times the optimum, might not do any harm and therefore iodization of a daily diet ingredient like salt is considered very safe. There are many foods containing significant concentration of iodine and deficiency of iodine among population consuming these foods in abundance may be rare.
Hyperthyroidism causes a general slowdown of the metabolism in the body as the calorie burning is dramatically affected creating a feeling of sluggishness. This in turn is supposed to promote putting on excess weight through fat deposits and increased water retention. Severe iodine deficiency can also cause brain disorders and gland enlargement while moderate deficiency can still show some of the above adverse effects. Excess iodine is reported to be also capable of manifesting symptoms same as hypothyroidism besides auto immune thyroditis resulting in infiltration of thyroid gland by lymphocytes blocking the ability of the gland to make the hormone. Though estimating the levels of TSH3 and TSH4 hormones in the blood is often used as testing a procedure to detect any abnormalities in thyroid activity, a positive result need not be a true indication of iodine deficiency and further testing also needs to be done if any symptoms associated with iodine deficiency still persists.
It may be recalled that the World Summit for Children in 1990 set a goal of 100% coverage of people through universal salt iodization program but till 2000 only 25% of the population was covered increasing to 66% by 2006 and to day more than 85% world population is covered by this unique endeavor of the global community. Even in India which saw a set back when ban on sale of uniodized salt was lifted in 2000, iodine deficiency increased dramatically among the population and fortunately better sense prevailed on the government which reintroduced the ban in 2005. In most states in India, latest survey seems to be indicating that 65% to 80% of the people have access to iodized salt. However no data is available regarding the prevalence iodine deficiency though it can be surmised that moderate to mild deficiency must be existing in the country. As massive urine testing of the people for excreted iodine has to be done to make any meaningful estimate of iodine deficient population, there is no way this could be done with meager facilities available in the country. Depending on any policy that bars sale of normal salt without iodization may not be the surest way of ensuring 100% coverage because in many rural areas salt is sold in loose without packing which is not fortified by iodine.
A country like Switzerland started its salt iodization program as early as 1952 mandating to contain 3.75 mg per kg and bringing it up to 20 mg per kg in 1998. Almost all countries now use this as bench mark standard for salt iodization but in the US and Canada iodized salt contains 77 ppm or 77 mg per kg iodine and in many countries salt intake through industrially processed and home cooked foods can be about 8-12 gm per day which corresponds to an iodine intake of 160-240 mcg from salt alone. Added to this consumption of sea foods further increases iodine availability. Sea vegetables like Kelp, Arame, Hiziki, Kombu, wakame are rich sources of iodine, varying in levels 500 to 2000 mcg per serving while Cranberry, yogurt, Milk provide about 55 to 400 mcg per serving. There fore iodine deficiency cannot be a critical factor in these countries. Is it possible that population consuming sea vegetables as in China, Japan and other East Asian countries do not have modern diseases that haunt the western world to the same extent because of [plenty of iodine contained in their diet? No report is available to confirm or repudiate this theory so far.
One of the imponderable factors that may influence iodine status in people is the extent of industry processed foods consumed and in this respect population in countries like the US have an advantage as more than 80% of foods consumed by an average family comes from out side their home. Any effort to to curb salt consumption can be attempted through the industry and that is what is happening in these countries where food sector is continuously being pressured to reduce salt in processed products and restaurant preparations. But this strategy may not work if processed food consumption by a family is low. What effect any reduction in salt intake will have on iodine status of the population? With salt reduction campaigns becoming more and more aggressive, there is a perceptible change in industrialized nations, the salt intake showing a downward slide. Also reported is slight increase in iodine deficiency population in countries like the US, probably consequent to the attempts to lower the salt intake. Under such a situation is there a case to increase the level of iodine in salt appropriately to meet body's demand for iodine through a lesser intake of salt? Probably yes as there does not appear to be any adverse effect even if the iodine intake is more than that required by the body. But in Canada and the US the fortification levels are comparatively high and there may not be any pressing reason to such a mid course correction. An upper limit of 1100 mcg of iodine has been determined to be tolerant to humans and hence no harm is going to be done by keeping higher levels of iodine in salts consumed by US population. A level of 100-200 mcg of iodine in the urine is considered an indication of adequate iodine intake while above 299 mcg it may be manifestation of excess intake. Similarly values up to 100 mcg can be interpreted as iodine deficiency sever, to mild depending on the actual test figures on individuals.