The thinking behind taking iodine or kelp is that in many parts of the world, goiters and thyroid disease are related to iodine deficiency. In the U.S. and other developed countries, iodine deficiency is not very common anymore, due to the addition of iodine to salt -- iodized salt -- and other food products. In fact, the most common forms of thyroid disease found in the U.S. -- autoimmune thyroid diseases like Graves' Disease or Hashimoto's Thyroiditis -- have nothing to do with iodine deficiency at all. Actually, thyroids are extremely sensitive to iodine, and you need to be careful about adding too much iodine to the diet as it can irritate or aggravate the thyroid. Most doctors say not to worry about some iodized salt, or the iodine present in a food item such as an occasional sushi dinner. But even many prominent alternative doctors such as Andrew Weil and Stephen Langer advise against taking iodine or kelp supplements for people with autoimmune problems.