[derefr]

Interesting. That sounds less like "being one dose away from having too much iodine" and more like "having no tolerance for iodine, such that even one dose is too much."

I guess another way to think about environmental chemicals is by analogy to poisons: if they were common in the environment, you'd have a tolerance to them, but since they aren't, you don't. You can build up a tolerance by parts, at which point the poison stops being one and just becomes another chemical the body handles.

[gwern]

Maybe. I don't know what the mechanism of thyroid shock is; as I said, iodization is such a good idea overall that it's merely a footnote in the cost-benefit.