The Japanese, who have the highest intake on the planet, which averages around 1000-3000 µg day a median of about 1200 µg per day (varies because it depends what you do for a living — you’re a fisherman or a businessman, etc.) They have more iodine toxicity especially, on the island of Hokkaido, where there’s consumption of a kind of seaweed that yields as much as 30,000 or even 40,000 µg of iodine per day (30 mg or 40 mg per day). And they have flagrant problems with iodine toxicity.
What does iodine toxicity look like? It’s a dramatic rise in your TSH (your thyroid stimulating hormone), meaning you become hypothyroid. That’s what happens when people are over exposed to iodine. That’s exactly what happens in Japan when people have too much iodine, such as those on an island of Hokkaido. They have to abstain from eating anything that contains iodine for several months, to recover. Not everybody recovers. Sometimes there’s some form of thyroid damage incurred, and it causes hypothyroidism. Iodine toxicity can also paradoxically cause goiter (an enlarged thyroid) I say paradoxically because goiter is typically from iodine deficiency, but iodine toxicity can also cause goiter.
Those very high intakes are really not part of the adaptive human experience. People are meant to obtain iodine in microgram quantities. Study after study has shown us that it is the intakes in the microgram quantities that normalize thyroid function. I have seen iodine toxicity on many occasions; people taking, for instance Lugol’s Solution or Iodoral®. These are the high potency iodine preparations, that have typically 12,500 µg, or more. Within a few months people start to gain a lot of weight, 20-30 pounds. They get very cold. Their hands feet are cold. They lose their hair. They retain water. Their coronary calcium scores, that we use to track coronary disease, skyrocket. Some of the biggest rises in heart scan scores occur when you’re hypothyroid. TSH’s go from 1.5, which is normal, to 20, 30, 40.