It is extremely rare for anyone in the modern world to have an iodine deficiency, due to the abundance of iodine in processed bread products and dairy products, as well as iodized salt. I bought in to the need for supplemental iodine a couple decades ago; not in excess amounts, just a reasonable supplement. And it appears that gave me thyroid disease, which was finally identified this year after I took a higher iodine supplement which caused dramatic symptoms. In every country around the world that began adding iodine to salt or water supply, they have tracked statistics that show an increase in thyroid disease in the years afterwards. For instance, Denmark increased their population's iodine intake by only 50 mcg per person, and saw a rise in Hypothyroidism, Hashimoto’s Thyroiditis and thyroid cancers. You can read more about that here: https://www.drchristianson.com/what-happened-with-denmarks-iodine-experiment/ and this doctor has written an excellent book, Thyroid Reset DIet, which goes into great detail. Every time we humans try to "fix something" on a large scale - we seem to make it worse!