Table salt additive is a term used to refer to two substances, iodide and iodine, which are added to table salt to improve its nutritional value. Iodide is a form of iodine that is found in some foods and is essential for the production of thyroid hormones. Iodine is an element that is necessary for proper growth and development and is also important for the functioning of the immune system. Both iodide and iodine are added to table salt to provide essential nutrients to the body.