Iodine or I is a trace mineral that is essential for making thyroid hormone. It regulates the body’s production of energy, supports growth and development and helps the body burn off excess fat. When it is converted into thyroid hormone, iodine helps support mental function and the health of the nails, skin hair and teeth. Thyroid hormone also helps the body convert carotene into vitamin A, absorb carbohydrates from the intestines and synthesize cholesterol. People with an underactive thyroid are often prescribed an iodine supplement.