Iodine is necessary for the body to produce thyroid hormone, and there are some schools of thought that insist iodine supplementation is always appropriate to address thyroid issues.
However, there is evidence that in some people iodine supplementation can aggravate or even cause autoimmune Hashimoto’s thyroiditis. Japan has the highest incidence of Hashi’s in the world and also has the highest dietary intake of iodine.
There is no question that we need iodine. When taking thyroid hormone medication, however, it may very well provide all the iodine one needs. When the T3 deiodinates into T2 and then T1, it is dropping an iodine molecule each time throughout the body.
A case study in the Journal of Pediatrics reported three infants being born with congenital hypothyroidism from mothers supplementing iodine (12.5 mg a day) during pregnancy.