Iodine is essential to life, but both deficiency and overdose can have severe health consequences.  The body needs iodine - a trace mineral - to make thyroid hormones which control the body's metabolism and many other important functions. Without sufficient iodine, your body is unable to produce these hormones, opening the door for a host of health complications including enlarged thyroid, hypothyroidism, fibrocystic breast disease, and various physical and mental disabilities during fetal development. On the other hand, excessive intake of Iodine can cause an enlarged thyroid as well as hyperthyroidism, thyroid papillary cancer and iodermia, a serious skin reaction. 

Environmental factors including soil concentration and use of fertilizers can affect the iodine levels of foods, and most foods that naturally contain iodine typically contain only small amounts. Due to iodine additives, processed foods provide sufficient amounts of iodine, but due to the numerous downfalls of processed foods, you're better off opting for the lower iodine-containing natural foods to supply your body's iodine. Sea vegetables, natural yogurt, grass-fed eggs and mozzarella cheese are all excellent sources of natural iodine. Fish and shellfish, while rumored to be excellent sources of iodine, can actually vary greatly regarding iodine content. As such, it is a good idea to not rely too heavily on fish as an iodine source. The use of iodized salt has dramatically increased the iodine intake of people in developed countries. It is important to keep in mind when switching to a healthier source of salt - especially if you go the extra step of ridding your diet of processed foods that contain iodine additives - your iodine intake may dramatically decrease as well. Iodine levels can be a bit tricky to maintain, so be sure to talk to Dr. Bossio before adjusting your diet or supplements for reasons related to iodine. Consultation with Dr. Bossio is especially important if you have a history of thyroid problems, poor dietary balance and deficient intake of iodine and/or selenium.

REFERENCES

Iodine. World's Healthiest Foods.
http://www.whfoods.com/genpage.php?tname=nutrient&dbid=69

Iodine: Fact Sheet for Consumers. Office of Dietary Supplements. National Institutes of Health.
http://ods.od.nih.gov/factsheets/Iodine-QuickFacts/.