Iodine is a trace alement found largely in sea water. There's a lot of iodine in seaweed and in the livers of fish like cod. If you live in a coastal area, you'll get iodine in your diet naturally. But go inland and iodine gets harder to find in nature. Fresh water flushes iodine out of the soil. Worst off are places that used to be covered with glaciers. When people don't get enough iodine in their diets, their thyroid glands have to work overtime to compensate. So the thyroid becomes huge, like an oversized heart. And so people living there have historically been afflict d with gouder.