lack of Iodine diminishes the reception of hormones. the body reads this as a deficiency in hormones and makes more, and more, and more until the gland exhausts creating estrogen dominance, vitamin A and D deficiency and type 2 diabetes. this is also why both hyper and hypo thyroidism is due to lack of iodine.
like dr brownstein says in his book, every hormone receptor in the body must have iodine. in fact, every cell in the body must have iodine. the body burden for sufficiency is 1500mg, not the 50 or so it was thought to be. the RDA prevents goiters, none of the rest of the problems Iodine deficincy causes. it didnt show up so much until we depleted the soils and injected huge quantities of the other halogens into our environment and bodies.