Thanks, that was extremely interesting, Emily. I was possibly iodine deficient during my first transition attempt which may have (at least in part) accounted for my very meagre breast growth at the time. This time, no problem on either count.
After doing some more digging, the issue seems tied to the thyroid gland (obviously, makes sense) and cis women with thyroid problems can experience breast size changes. One has to be
extremely careful with iodine though - too little creates deficiency and that is a common Western malaise but it's easy to have too much and that will cause hyperthyroidism which is worse and dangerous.
So yes, iodine, like many dietary nutrients, is important for health and breast growth... but for anyone who is might now be contemplating ODing on iodine supplements in the hope of bigger boobs be advised it is a very, very,
very bad idea.