I honestly don't know for sure but after listening to Jerry Brunetti's supplement list (he takes 1200mcgs and has for a long time) and looking at high Iodine intake and low selenium research on thyroid I decided to be "conservative" and go up to 600mcgs. I've been there for about 4 weeks and lots of the low thyroid episodes I was having disappeared.
By low thyroid I mean on Iodine i would occasionally have periods where I felt wiped...like climbing up 5 stairs looked like a huge ordeal. Other days I would feel fabulous so it scared me to vacillate like that. Once I upped Selenium it went away so I'm assuming my thyroid was getting stressed from too much iodine.
There are some fabulous posts here and on the yahoo group called "iodine" on research on selenium's interactions with Iodine and the thyroid. Try a search on these.
Also when iodine4health.com is back up search there too.
I would think more people here will also post on selenium's role with iodine.