In Australia and New Zealand, natural iodine levels are low in soils, and this affects the levels of iodine in foods such as vegetables, grains and livestock i.e. cattle and sheep.
Recent trends in lifestyle factors, for example using sea salt rather than iodised salt in cooking, have also decreased the amount of iodine in our diets.
We also used to get iodine from milk. Over the last 40 years dairy farmers used iodine based solutions to sterilise milk containers, but during the last five years they changed to chlorine-containing sterilisers.