The use of iodized salt has certainly reduced most iodine deficiency. It contains about 76 mcg. of iodine per gram of salt. The average person consumes at least 3 grams of salt daily, exceeding the RDA for iodine of 150 mcg. Many authorities feel (and I believe) that commercial iodized salt is overused and has other drawbacks. It contains aluminum and other unneeded chemicals and may contribute to other problems. Fast foods may be very high in iodine because of the added salt. Adding iodine to salt is part of the paternalistic thinking of the industrial age, not counting on people to learn or adapt, "just put it in their food or water and save them from their own ignorance." There are healthier ways to obtain iodine than in table salt; eating fish, especially fresh ocean fish, is probably the best, as it also may help reduce cholesterol and cardiovascular disease risk. Sea salt from the ocean water is a natural source of iodine, although it is not nearly as high in this mineral as "iodized" salt.
Dietary iodine content may vary widely, depending on the iodine content in the soil in which food grows. Plants grown in or animals grazed on iodine-rich soil will contain substantial amounts of iodine. Milk and its products may be sources of iodine when the cows have an iodized salt lick in their pasture. Eggs may also be a good source when iodine is in the chicken feed. Bakers may add iodine to dough, so some may be present in bread. Other foods that may contain iodine, especially when the soil is good, are onions, mushrooms, lettuce, spinach, green peppers, pineapple, peanuts, cheddar cheese, and whole wheat bread. More and more, people are eating wholesome, natural foods, avoiding iodized salt, so they must eat more of the iodine-rich foods, such as the sea vegetables, or obtain iodine from a general vitamin-mineral supplement to make sure they are getting adequate amounts.
Functions: Iodine is an essential nutrient for production of the body's thyroid hormones and therefore is required for normal thyroid function. The thyroid hormones, particularly thyroxine, which is 65 percent iodine, are responsible for our basal metabolic rate (BMR)-that is, the body's use of energy. Thyroid is required for cell respiration and the production of energy as ATP and further increases oxygen consumption and general metabolism.
The thyroid hormones, thyroxine and triiodothyronine, are also needed for normal growth and development, protein synthesis, and energy metabolism. As thyroid stimulates the energy production of the cellular mitochondria and affects our BMR, it literally influences all body functions. Nerve and bone formation, reproduction, the condition of the skin, hair, nails, and teeth, and our speech and mental state are all influenced by thyroid as well. Thyroid and, thus, iodine also affect the conversion of carotene to vitamin A and of ribonucleic acids to protein; cholesterol synthesis; and carbohydrate absorption.
Iodine is picked up by the thyroid and combines with the thyroid hormones and amino acid tyrosine to make the thyroid hormone precursors diiodotyrosine, diiodothyronine, and monoiodotyrosine and, then, the hormones T3 and T4. These hormones are then carried through the body by a protein called thyroid binding globulin (TBG).
Uses: Supplemental iodine may be helpful in correcting hypothyroidism and goiter caused by deficient iodine intake, and it may reverse many of the symptoms of cretinism if given soon after birth. Thus, iodine's main use is really in the prevention or early treatment of its deficiency diseases.