Swiss geology (retreat of the glaciers 10000 years ago) meant that the normal local products that would give a population iodine (milk and eggs) were themselves

Swiss geology (retreat of the glaciers 10000 years ago) meant that the normal local products that would give a population iodine (milk and eggs) were themselves iodine-poor. A few parts of Switzerland which were not glaciated (i.e. Jura) did not have iodine deficient populations. Other places in the world had different geology and this different levels of natural iodine.