Calling all iodine mavens! "too much" iodine??

OK, so this morning, I brought up the subject of Iodine and how I am
experimenting with it to raise my thyroid functioning. The person I spoke with,
who has studied biology (but her Ph.D. is in physics) said to me "But you know there
is such a thing as TOO much iodine, as in HYPERthyroid." I disagreed, saying that
there was not enough Iodine in either case. Then I thought, "uh-oh, I may be in over
my head here" because though it seems to me I've read that that is the case,
that there may be a malfunction of the thyroid in either direction due to the lack of iodine,
I am not really sure how the mechanism works. Vulcanel? anyone else?
thanks