Paul Jaminet has written some good pieces on iodine. Please check them out (some of the segments come in backward order, such as part 2 on top of part 1).
The summarized version is that iodine and selenium are both very important and must be in a particular balance. ‘Autoimmune’ thyroid problems can often be improved with increased selenium intake (food or supplements). With adequate selenium status and no autoimmune symptoms, quite high doses of iodine are acceptable and MAY even be beneficial. But SO LONG AS the autoimmune problems are going along, a more modest intake of iodine and higher selenium intake may be warranted. It’s hard to give exact numbers on this, but Paul tries to give some guidelines in his posts. Up to a point, more iodine causes increased T4 production in the thyroid which requires free radical generation. Selenium is designed to quench the radicals here, and low selenium will lead to a sort of destruction of the thyroid by its own activity. Hence ‘autoimmune’ thyroid-itis. Thus, until selenium status is improved–if, in fact it was low to start with–increased iodine may be trouble.
High rt3, Low t3:
But one thing Paul does not touch on is another situation, where people are high reverse t3 (rt3) and low t3–so called ‘euthyroid sick syndrome’, or ‘low t3 illness’, or several other names. This is NOT an autoimmune problem, per se. In these cases, increased iodine may also be miserable, and here’s why. Increased iodine–at least up to a point, increases T4 production from the thyroid. In healthy people, the liver then activates some T4 into t3 and deactivates some T4 into rt3. But if the patient is starving or low carbing or anorexic or whatever, the liver deactivates a higher percentage, leading to higher rt3 and lower t3. IN THIS CASE, the higher production of T4 will only lead to more rt3 which can competitively inhibit t3 and make a starving person even more miserable. Thus anorexic recoverees may also ‘feel’ better by not overdoing the iodine during their recovery.
The liver is not the only location for T4 and t3 conversion, but it is a primary site so liver energy status is important. Anything that increases the energy status of the liver (glycogen from carbs, short chain fats from butter, coconut oil or beneficial fibers) will increase T4 to t3 conversion. Anything that depletes liver energy stores (fasting, low carbing, increased endotoxin absorption from intestines) will decrease T4 to t3 conversion, and increase T4 to rt3 conversion (and deactivation of t3 into t2, I think). It should also be stated that selenium is needed in the liver here to make the T4 to t3 conversion, so low selenium can cause low t3 and high rt3, just as low selenium also messes up autoimmune thyroid problems.
I want to mention one more thing about selenium. There are many antioxidants in the human body, and all of them either contain a mineral or require one for antioxidant generation. The most common minerals used as antioxidants, if I’m not mistaken, are selenium, copper, and zinc. I have seen some studies where a low copper diet (or high zinc, since zinc can inhibit copper absorption and retention) CAUSES low selenium activity. Here is one that I quickly came upon again, but there are others I can’t locate right now.
The point with this last comment is that selenium status can be greatly affected by copper and zinc status. I wouldn’t be too worried about this for most people, but modern ‘paleo’ diets (high red muscle meat with zinc; low beef liver which is the best source of copper) are asking for copper deficiency, which can provoke a selenium deficiency.
Lulu, coming back to you now. I would read Jaminet’s article. I would then consider supplementing selenium (ideally something organic, like L-selenomethionine) or at least monitoring selenium intake from diet via a nutrient tool like nutritiondata.com.
Best selenium sources: anything grown in Brazil, especially nuts (hence Brazil nuts); eggs; fish and shellfish; meat of all kinds, especially kidneys; some grains and vegetables, but this is VERY soil dependent.
Iodine sources: various seaweeds and kelps have most of anything; fish and shellfish; dairy; eggs; some meat and vegetables, but this is VERY soil dependent; some sea salts (Real Salt has about 100 mcg per 5g teaspoon; Celtic Salt has a negligible amount)
‘Iodized’ salt has iodine added to a refined NaCl, with some dextrose and sometimes alkaline powder added to it to help prevent ‘caking’ of the iodine. You’ll hear different things about this, but I’m not a fan.