Iodized salt is so commonplace in the U.S. today that you may never have given the additive a second thought. But new research finds that humble iodine has played a substantial role in cognitive improvements seen across the American population in the 20th century.Iodine is a critical micronutrient in the human diet — that is, something our bodies can’t synthesize that we have to rely on food to obtain — and it’s been added to salt (in the form of potassium iodide) since 1924. Originally, iodizat...