Where did Western people get iodine before it was necessary to add it to salt? Has our soil been so depleted that iodine is no longer present in the vegetables grown in it?
Some lived near the sea and had high seafood diets, but most were just iodine deficient, which doesn't stop a population from surviving, though it leads to suboptimal outcomes in a number of dimensions.
There is this wierd pervasive mythology that before modern times people lived in an ideal state (at least in terms of nutrition), so any present deficiency from the ideal must reflect a difference between modern and premodern society. Past conditions were at least minimally adequate for survival and reproduction, or we wouldn't be here, but there's no real basis for assuming that they were in any way ideal.
Let's repeat that because it's important and counterintuitive: Those conditions were ideal for us because our species changed to fit the conditions.
What's happened since is a crazy rollercoaster ride of life conditions changin much faster than evolution has any chance of keeping up with, and premodern society in the sense of preindustrial can in no way be presumed to be ideal.
Hundreds of thousands of years is not a really long time in evolutionary terms, and evolution doesn't necessarily, even given a long time, get out of a good-enough local optimum to “extremely well adapted”.
It's also debatable whether conditions in which humans evolved are really a steady state.
More to the point, humans being ideal for the conditions—what the argument from evolution suggests—is not the same as the conditions being ideal for humans.
I think violence, poverty and disease were the bigger factors.
All I'm claiming is that our digestive system is adapted to what we had to eat where our species evolved.
Potatoes are a New World crop. Medieval European peasants didn't have them.
No, you wouldn't, as a European of any social class, except maybe in the very late middle ages at the boundary of the Renaissance; potatoes were a New World import in the 16th century, which might just still be considered the Middle Ages in some parts of Europe.
It was an important source of protein in centuries past, and was traded all over Europe. It would've also been an effective way for inland residents to get iodine.
It's possible this has some contribution, but it's not the main source.
> It's not inherent in the dairy itself
Yes, it is; in cows (and humans) mother's milk is where young who aren't eating anything else get their iodine.
> otherwise we could just eat the cow's grass to obtain iodine
Well, except for the fact that grass doesn't work well in the human digestive system, and you'd have to eat a lot of it, sure.
In Australia the situation is a lot worse, she said, because our soils are so depleted. No just of Iodine but many other nutrients.
Since the identification of the widespread deficiency and it's effects which motivated iodization of salt was first in the West among Western people, probably not meaningfully. Unlike sunlight which is highly latitude dependent, iodine availability is much more location dependent, and the high availability places (places with access to fish, approximately—both saltwater and many freshwater locations) are also where pre-civilization human populations tended to be most concentrated.
This is one of the many little invisible progresses that has steadily made our life expectancy increase all over the 20th century.
Iodine is so soluble that it's quite scarce other than in the ocean. And yep, people who lived inland (and thus didn't eat seafood) in premodern times were often iodine deficient.