if you don't have enough iodine in your diet it's worse for you.
Iodine is a concern for vegans. Iodized salt has been demonized by the health food industry, but it could be a good source of iodine for us.
Iodine Deficiency Reported in Vegetarians and Vegans
Michael Greger, M.D.http://www.veganMD.org
Last month [Oct 2003], yet another article appeared on iodine deficiency in vegetarians and vegans . Quoting from the paper: "One fourth of the vegetarians and 80% of the vegans suffer from iodine deficiency..." Only 9% of the meateaters were deficient. The milk drinkers were protected in part because iodine containing disinfectants are used to clean the milk processing equipment which kind of leach into the milk. None of the vegetarians and vegans were eating sea vegetables. And none were using iodized salt--they were all using "natural" sea salt, which has significantly less iodine. Iodine deficiency was actually a prevalent problem in the U.S. before the iodization of salt became a common practice in the 1920's.
So, vegetarians who don't eat sea vegetables or use iodized salt should consider supplementing their diet with iodine. I don't encourage people to add salt to their diet--it's not good for your bones--but if you do use table salt, use iodized salt. For more information, see the British Vegan Society's iodine page. The best source, though, is sea vegetables (seaweed).
Sea vegetables have lots of B vitamins and lots of minerals, particularly the trace minerals, like iodine. The only problem with seaweed is that you can actually get too much iodine. The World Health Organization places the safe upper limit of iodine intake at 1000 mcg per day. And it's less for kids-like 300 mcg may be too much for a five year old. See my handout on nutrients for the amounts found in common seaweeds.
 Annals of Nutrition and Metabolism 47(2003):183
 Journal of the American Dietetics Association 79(1981):17.