Here's an informal observation.
The healthiest people are the most iodine deficient.
The healthier you are, the more likely you are to:
--Avoid junk foods--30% of which have some iodine from salt
--Avoid overuse of iodized salt
--Exercise--Sweating causes large losses of iodine.
So the healthy-eating, exercising person is the one most likely to show iodine deficiency: gradually enlarged thyroid gland (in the neck), declining thyroid function. Over time, if iodine deficiency persists, excessive sensitivity to iodine develops, as well as abnormal thyroid conditions like overactive nodules.
Even subtle levels of thyroid dysfunction act as a potent coronary risk factor.