What is the actual upper limit for the daily intake of iodine, and what's up with Japanese intake?

Hello. Upon finding out I was deficient in iodine I began taking kelp tablets (one tablet containing 150mcg of iodine once daily), but began reading up on iodine out of curiosity.

It seems that iodine has many benefits beyond thyroid regulation and according to some sites increasing intake may be a good idea, so I have been considered upping my own kelp intake, but I am concerned about the risks involved, especially overdose. I have been hearing about something called “the Iodine project,” which proposes that people take at least 12 MILLIGRAMS of iodine per day for improved health (the actual figure ranges from 12.5 to 50 mg, and, in diabetics, up to 100 mg/day.) But isn’t the upper limit intake only 2 mg? (Other sources say the limit is 1mg down to 600mcg, give or take according to your age/gender.) What’s even more surprising is that some doctors, likeDonald W. Miller, Jr., MD, approve of this project that promotes this “more is better” party.

And also, I have been reading how the Japanese typically eat a lot of kelp and high-iodine foods, and that the average daily intake for them is around 12-13mg. Again, is this true? If 2mg is toxic, why aren’t the Japanese getting sick from overdose?