Gabe Mirkin, M.D.
Sea salt and table salt both contain sodium chloride. Sea salt also contains small amounts of magnesium chloride, magnesium sulfate and calcium sulfate, which are nutritionally insignificant. Iodized salt, sea salt, kosher salt and seasoning salts are all treated the same way in your body.
You need to eat foods that contain iodine for your body to be able to make thyroid hormone. The best sources are iodized salt and seafood. Plants can be a good source, but only if they are grown on iodine-rich soil. A study in the Annals of Nutrition and Metabolism (September-October 2003) showed that vegetarians are at increased risk for iodine deficiency that causes low thyroid function. In this study, 25 percent of vegetarians and 80 percent of vegans had low blood levels of iodine, compared to only nine percent of people who eat both plant and animal products.
While iodized table salt is a good source of iodine, sea salt often is not. If you don't use table salt or eat seafood, you may want to get a blood test for iodine. If your iodine level is low, you need to add iodine sources to your diet or take iodine pills.