The body needs relatively little iodine to maintain health. The RDA for adults 19 years of age and older is 150 micrograms a day. It’s estimated that the iodine intake from food in the US is usually around 200 to 300 micrograms a day for men and 190 to 210 for women. Very few foods are reliable sources of iodine because the amount of iodine in foods varies according to soil, irrigation, and fertilizers. Saltwater foods, both fish and plants, usually have higher amounts because marine species concentrate iodine from seawater. Good food sources include saltwater fish, shrimp, seaweed, iodized salt, and white and whole-wheat breads made with iodized salt. Iodine is also added to dairy cattle feed and used in sanitizing solutions in the dairy industry.
Iodine has been voluntarily added to salt in the US since 1924 to help combat the iodine deficiency. For many people, iodized salt is their primary source of iodine and approximately one half of a teaspoon of iodized salt meets the RDA.
Source: Thompson, Janice, Melinda Manore, and Linda A. Vaughan. The Science of Nutrition. San Francisco, CA: Pearson Benjamin Cummings, 2011. Print.