Potassium iodide (KI) is an ionic salt that is a source of the essential element, iodine. Potassium plays an important role in human metabolism and is essential for proper muscle function, certain neurological mechanisms and as an electrolyte. Iodine is required by the body, meaning that humans must have a continual supply in their diet in order to maintain good health (see table below for the Recommended Dietary Allowance based on age). Potassium iodide consists of 76.5% iodine by mass.
Optimal iodine intake is necessary for normal thyroid function. The thyroid gland takes iodine from the blood and incorporates it into thyroid hormone, which is then released into circulation when needed. Thyroid hormone, or thyroxine, regulates multiple physiologic processes that include growth, development, metabolism and reproductive function. It also aids in the conversion of food to energy and the maintenance of body temperature.
The thyroid isn't the only organ that uses iodine. The breast, prostate gland and skin also take up iodine for use in their intracellular activities.