Use of potassium iodide for thyroid protection during nuclear or radiological emergencies

Overview

During a nuclear accident, radioactive iodine may be released in a plume, or ‘cloud’, and subsequently contaminate soil, surfaces, food, and water, as well as settle on an individual’s skin and clothing resulting in external exposure. Radioactive iodine deposited during external exposure can be removed by washing with warm water and soap.

Another type of exposure with greater risk to human health occurs when radioactive iodine is either inhaled or ingested or when substances, such as contaminated food, milk or water, are consumed. Internal exposure, or irradiation, occurs when radioactive iodine enters the body and accumulates in the thyroid gland.

The thyroid gland is at particular risk from irradiation from radioactive iodine because the thyroid uses iodine to produce hormones that regulate the body’s metabolism. The thyroid gland does not differentiate between non-radioactive and radioactive iodine. Uptake of radioactive iodine may increase the risk of thyroid cancer, particularly in children. The younger the age at exposure, the higher the risk is for developing thyroid cancer.

In this situation, potassium iodide is used to protect, or block, the thyroid from irradiation. Commonly known as thyroid blocking, taking potassium iodide (KI)1 before or at the beginning of exposure to radioactive iodine blocks the uptake of radioactive iodine by the thyroid gland, thus reducing exposure of the thyroid to internal radiation.