When your body's having trouble converting T4 to T3, consider that you may need selenomethionine 200 mcg to go with the iodine. Iodine is part of the raw materials for thyroid hormone, and selenium is one of the agents in the conversion of T4 to T3. Iodine taken without selenium will eventually use up your selenium stores. So, you have all raw materials and no conversion agent. Likewise, taking selenium without iodine to fill the production line will shortly cause you to run out of T3. Either way, hypothyroid symptoms. Those aren't the only ways in which hypothyroid can show itself, but it's a basic recommendation to take selenium with iodine.