That practice can be problematic for many people, because many cases of autoimmune thyroid disease -- which is by far the most common cause of thyroid conditions in the U.S. -- are not due to iodine deficiency.
The likelihood that your thyroid problem is caused by iodine deficiency is a factor of your geographic location, diet, and use of salt and iodized products, but the odds are, you are not iodine deficient.
Your physician or nutritionist can test your iodine levels via a urinalysis test, if you wish to be evaluated. If, like many patients, you decide on your own to try kelp, iodine, or one of the many thyroid-supporting supplements (almost all of them contain high amounts of iodine or kelp), to see if they can help you, be aware of the risks. A percentage of patients are very sensitive to iodine/kelp supplementation, and find that it aggravates their thyroid problem.
Personally, I'm one of those people who simply does not do well with much in the way of supplemental iodine. I do fine
with food that contain iodine -- such as seaweed or seafood. In fact, I periodically find myself craving sushi and a good seaweed salad, and can eat it with no after-effects whatsoever. But the several times I have tried iodine or kelp supplementation in any form -- beyond the very small amounts of iodine contained in some supplements -- I have had what I call an "iodine crash."
Within a day, I noticed my thyroid enlarging slightly (goiter), and feeling tender. Within three days, I became exhausted and achy all over my body. Most of the thyroid support supplements have high amounts of iodine, or kelp, claiming that these are essential nutrients for the thyroid. Be careful -- they may be a help to you, but like me, you may also be sensitive to supplemental iodine in pill form, and find yourself having an iodine crash.
Some people are so sensitive to iodine that they really shouldn't even take the small amount of iodine you would find
in most multivitamins. For that group, there are several supplements that contain no iodine (they also happen to contain no iron as well, which means they can safely be taken at the same time as your thyroid medications.) (Note: if you are taking iron supplements, you need to take them at least 3 to 4 hours apart from your thyroid medication.)
Note: If you would like more information on multivitamins without iodine, click here
Source: Laurberg P, et. al. "Environmental iodine intake affects the type of nonmalignant thyroid disease," Thyroid. 2001 May;11(5):457-69