History of U.S. Iodine Fortification and Supplementation, Nutrients, November 2012
Approximately 120 countries, including Canada and some parts of Mexico, have adopted mandatory iodization of all food-grade salt , although the extent of implementation efforts in individual countries is unknown.
In contrast, fortification of salt with iodine in the U.S. is voluntary, and the FDA does not mandate the listing of iodine content on food packaging. Furthermore, it is assumed that the majority of salt consumption in the U.S. comes from processed foods, in which primarily non-iodized salt is used during production .
Although iodized salt in the U.S. is fortified at 45 mg iodide/kg, 47 of 88 table salt brands recently sampled contained less than the FDA’s recommended range of 46–76 mg iodide/kg
So, in the US, our diets are awash in sodium and salt, and not much of it contains iodine.