I know the question was specifically about Western countries, but this comment (unintentionally) makes it sound like it's only been a western problem. This was

I know the question was specifically about Western countries, but this comment (unintentionally) makes it sound like it's only been a western problem. This was a big problem in China and is still an issue today [1] (although the numbers in that article aren't really specific to China). https://en.wikipedia.org/wiki/Iodine_deficiency_in_China https://en.wikipedia.org/wiki/Iodine_deficiency_in_China