While my reply immediately above may at first glance to some appear to contain disconnected thoughts, they instead in reality embody the notion that we need to supplement ourselves with many different things we are not getting, just not on a constant basis.
God made us to have organs that are able to concentrate and hold minerals when diet provides them. Thyroid can hold and concentrate iodine, uterus and prostate can hold and concentrate zinc, thymus with manganese, etc. I think it is helpful to sporadically supplement the trace minerals, knowing the organs will grab them. There is a window, we don't want to be insufficient in any of them, but at the same time we do not want to provide too much. There is a great deal of evidence showing that for things necessary and good for us, having too much of them can cause certain pathologies. With iodine, the tolerance window appears to be pretty wide. For others, such as nickel, more than a tiny amount can be very very bad, yet a tiny amount is necessary. Nature works with trace amounts best of some things.