In 1997 I was taking 10 grams of vitamin C every day and feeling great just as I expected. However, in the middle of feeling great I developed hyperthyroidism, which as you probably know is a very serious disease. In my subsequent studies I found that taking very large amounts of vitamin C can deplete copper. As you will read elsewhere, I feel that copper deficiency is a key factor that causes hyperthyroidism.
Other nutrients seem to work the same way. For example, taking excess vitamin E seems to aggravate hyperthyroidism because it depletes selenium, the mineral that works with vitamin E. Zinc, which is on every nutritionist's "must take" list, can deplete copper if taken in excess without also supplementing copper. The minerals manganese and chromium work as a pair in various functions and taking either one of them without the other can deplete the one not taken. These minerals are important for thyroid health.
Copper and iron work together to form hemoglobin. If you become deficient in either one, you can get anemic--either iron-deficiency anemia or copper-deficiency anemia. Many people have reported to me that they have been found anemic by their doctors and been given large amounts of iron to correct the problem. Usually the anemia failed to improve. One woman took close to 200 mgs of iron per day for a long time and when her anemia didn't improve, her doctor put her in the hospital for an iron-transfusion, a process in which an extremely large amount of iron is given intravenously. Not only did this not help, but she became extremely ill and was ill for days.
When these people who told me about these experiences had thyroid disease, my first guess was that they were deficient in copper and not iron. When they began supplementing with copper, their anemia improved. I believe that taking the extra iron without copper further depleted their copper and worsened their thyroid health. http://www.ithyroid.com/supplement_list.htm