It is often stated that prior to around 1980 it was mandated that iodine be added to all commercially baked goods in the United States and that in the 1960s, for instance, each and every slice of bread contained 150mcg iodine.
I have never been able to find the directive that iodine be added to bread, and I have searched extensively. I do know though, that potassium bromate was in use as a dough conditioner as early as the 1920s, so brominated flour was nothing new...
My personal belief that the mandate to iodize baked goods was a response to the rising rates of thyroid cancers amongst the "downwinders" due to atmospheric testing in the 1950s in Nevada. These tests exposed people to radioactive iodine 131. We'll probably never know why, exactly, iodine was present in baked goods throughout the sixties and seventies, but here is a hint, at least, as to why it was removed in the eighties.
Without further ado:
re: iodization of salt:
re: iodine fortification in general: