[gwern]

> but this didn't push anyone from "getting a tolerable amount of iodine with the excess just excreted" to "having a hyperiodine problem." There was nobody exactly one dose away from having too much iodine, because we just don't consume that much iodine.

Actually, there was: 'thyroid shock'. Iodization in the USA was accompanied by a wave of, I think, a few thousand deaths on net when people who grew up iodine-deficient were suddenly exposed to iodized salt. (This was covered by one of the historical papers I cite in http://www.gwern.net/Iodine although I forget which.)

Of course, the benefits of iodization were on net huge and I'm very much a fan of iodization, but it would be wrong to say nobody was hurt by the introduction of iodized salt.

[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.