We evolved from life forms in the sea where there is lots of iodine. Fish have thyroid glands and hormones and obviously it is not to regulate their body temperature, however thyroid hormones probably regulate mitochondrial activity. I expect that there will be roles for iodine that are never understood.
With low iodine, every system is compromised directly and then there are cascading secondary effects when the effects of compromised systems affect each other and the rest of the body and brain. Control systems can be dysfunctional.
When one is iodine deficient, the thyroid can be enlarged and nodular. One can already be in a hypo state with TSH independent nodules producing T4 and T3. However, thyroid levels can still be low as iodine is low. When you restore iodine levels, these hidden hyper cases are then exposed in the population. We use iodine to avoid goiter and metal retardation in society. During a transition to iodized salt, there will be these transient cases. Once a population is using iodized salt [or bread], there will be an over all benefit and the transient problems will not occur in the future. I also often state that iodization programs do not create hyperthyroidism, but will bring these cases forward in time. Iodine is not responsible as the cause. I also point out that when one avoids iodized salt, one goes from hypo to hyper - clearly a lack of iodine causes both the hypo and hyper states.
When one is iodine deficient, I advocate a 750mg IR program. Many can do this in 15 days. If you do this over 2 months, the result will be the same, however, benefits will be both delayed and less obvious. 50mg/day provided dramatic effects for me. However, I did need to reduce the dose after a week as my digestion was affected. Because I was on TRT and my TT, FT and E2 were all in good shape, I was in a position to feel good once my iodine levels were up; and my thyroid obviously responded well.
After iodine replenishment, I suggest lower maintenance doses. Myself, I take 6mg every two-three weeks. I disagree with ongoing high dose iodine as I see no reason to do that.
No one is allergic to elemental iodine.