ZRT Laboratory

Potassium Iodide and the Nuclear Crisis in Japan
4/24/2011
from Iodine: Deficiency, Sufficiency, Testing blog

1) Why is radioactive iodine a problem after a nuclear reactor meltdown?

Radioactive isotopes are released after nuclear reactor disasters and nuclear detonation. The most common isotopes are: iodine-131, cesium-137, strontium-90 and plutonium-239.

The thyroid gland is particularly vulnerable to radioactive iodine-131 (I-131) because it takes up and stores iodine for the process of thyroid hormone synthesis.  To concentrate iodine the thyroid gland uses an ion pump, the Sodium Iodide Symporter (NIS), which transports iodide out of the bloodstream into the thyroid follicular cells.  Iodide levels in the thyroid can reach 40x what they are in circulating blood1. Once in the cells of the thyroid gland, iodide is activated and attached to a protein called thyroglobulin. Iodinated thyroglobulin is further processed to either of the thyroid hormones, thyroxine (T4) or triiodothyronine (T3), and eventually released into the bloodstream.

The body cannot differentiate between non radioactive iodine-127 and radioactive iodine-131 that is released from nuclear reactor disasters. 

2)  Who is more vulnerable to radioactive iodine?

Populations living in iodine-deficient regions are more vulnerable because their thyroid glands will take up more radioactive iodine than in iodine-sufficient regions2. In areas of the world with iodine deficiency there is an increased number of individuals with goiter, the thyroid’s attempt to concentrate as much iodine as possible from their low-iodine environment. Because our source of iodine originates from the ocean, populations far removed from the ocean and mountainous regions are more likely to suffer from iodine deficiency. Countries like Japan, which are surrounded by ocean, are not iodine deficient, whereas mountainous regions of Europe and central Africa are more likely to be iodine-deficient. It is important to note that those who are iodine deficient absorb nearly twice as much radioactive I-131 as those who are iodine sufficient; a great reason to test your daily iodine intake2,3.

3)  How does nonradioactive iodine protect the thyroid against radioactive iodine released from nuclear reactor accidents? 

If the thyroid becomes saturated with non-radioactive iodine-127, a result of iodine being present in foods commonly consumed or from taking large amounts of supplemental iodide, the thyroid gland will become saturated with non-radioactive iodine, preventing further uptake of radioactive iodine-131. While radioactive iodine can still enter the body through the food chain (mostly milk and green leafy vegetables) or through inhalation, it will not be taken up and retained in a thyroid gland saturated with non-radioactive iodine, and will be rapidly flushed from the body with >97% seen in the urine4.

4) What type of iodine/iodide should be taken?

There are many forms of iodine/iodide available. The sodium iodide symporter concentrates iodide, not iodine. Iodide can be found in supplements such as KI (potassium iodide), NaI (sodium iodide or iodized salt), Iodoral and Lugols (a mixture of molecular iodine and potassium iodide), SSKI (saturated solution of potassium iodide) and a multitude of other compounds. KI (potassium iodide) is the most common supplement taken during radiation exposure. If a supplement contains both iodine and iodide, make sure that the amount of iodide present is equal to the dose needed for thyroid protection.

For more Q&A on potassium iodine, go to Iodine: Deficiency, Sufficiency, Testing blog