Potassium Iodide and Nuclear Emergency
When a nuclear reactor melts down, an explosion can occur that spreads radioactive iodine and other carcinogens into the atmosphere. Once released in the air, radioactive iodine can then be inhaled into the lungs. Radioactive iodine can also penetrate the food and water supply, leading to further contamination and potential exposure. Any of these pathways into the body can lead to what is called internal contamination. Once internal contamination with radioactive iodine occurs, the body immediately begins to absorb this compound. Nearly all of the absorption of radioactive iodine occurs in the thyroid gland, leading to thyroid damage and a dramatic increase in cancer risk, particularly for young children.2
Is there a real threat?
People are very concerned now, but the reality is that there is unlikely to be a problem that reaches the United States. People are imagining a nuclear explosion like an atomic bomb which is unlikely at the Japanese plants. The current explosions are not related to nuclear types of explosion. They are caused by certain gases (mostly hydrogen) that can build up and ignite, but it is not a nuclear/atomic bomb type of explosion. Also, the nuclear event at Chernobyl cannot be compared to what is going on in Japan. Chernobyl reactors used more dangerous graphite materials in their reactors and were built without a containment building. The Japanese plants use a different reactor technology and are encased with a containment building that the reactor at Chernobyl didn’t have.
The Thyroid Gland: Essential to Health
Preventing damage to the thyroid gland is critical to the short-term and long-term health of those exposed to radioactive iodine. Positioned at the base of the neck, the thyroid gland produces thyroid hormone, which has effects on every organ, tissue, and cell in the body. These effects relate to energy levels, heart rate, muscle strength, skin health, menstrual cycles, cognition, and cholesterol metabolism.
The thyroid gland is especially important to growing children. Not surprisingly, children are believed to be more vulnerable to the effects of radiation. Studies suggest that exposure to radioactive iodine during childhood is associated with a greatly increased risk of thyroid cancer in later life.3 Children not only have greater susceptibility to radiation-induced cancer, they also have longer life expectancies compared with adults, giving latent cancer a longer time frame to develop.
Potassium Iodide Offers Protection
Many experts believe that the compound potassium iodide can protect individuals from some of the harmful effects of radiation exposure. This protective effect occurs because potassium iodide blocks radioactive iodine from being absorbed by the thyroid gland.4 The thyroid cannot distinguish between radioactive iodine and potassium iodide. Once the potassium iodide is taken and the thyroid gland becomes saturated with the compound, no more radioactive iodine or potassium iodide can be absorbed for the next 24 hours.
What is potassium iodide? Potassium iodide is a salt of the stable form of iodine. Stable iodine is a naturally occurring chemical element that is used in the body to make thyroid hormones. Potassium iodide is also a stable form of iodide that is used for medicinal purposes. The source of most of the iodine used in the body is from food. Potassium iodide is often added to table salt, and this is known as “iodized” salt.
What about iodized table salt? Iodized table salt contains sufficient iodine to keep most people healthy in most situations, but it does not contain enough iodine to prevent radioactive iodine from entering the thyroid gland. Iodized table salt is not a replacement for potassium iodide.
Potassium iodide cannot provide a protective effect once the thyroid gland has been damaged or destroyed by radioactive iodine.4 In addition, potassium iodide cannot protect other parts of the body from exposure to radioactive iodine. Furthermore, potassium iodide has no protective effects against radioactive elements other than radioactive iodine.4 It is highly effective in protecting against radioactive iodine.5
The rate at which the potassium iodide is absorbed into the blood helps determine how effective it will be in protecting against the effects of radioactive iodine exposure. It is very important how much time elapses between exposure and contamination with radioactive iodine and the use of potassium iodide. Obviously, the most rapid use of potassium iodide possible allows for the maximum protection against radioactive iodine. Its efficacy is greatest when administered immediately before the exposure, and it has greatly diminished clinical value when administered 12 hours or more after radiation exposure.
Using Potassium Iodide
What dose of potassium iodide is available? Potassium iodide is approved by the Food and Drug Administration (FDA) and is available as an over-the-counter drug in liquid and tablet forms. The recommended doses usually range from 65 to 130 milligrams (mg), and potassium iodide tablets are available in 65 mg and 130 mg tablets. The liquid form provides 65 mg of potassium iodide in each milliliter (mL) of liquid.
What are the typical doses of potassium iodide? The FDA recommends the following doses following exposure and contamination with radioactive iodine:6
- Newborns up to one month of age: 16 mg of potassium iodide, which would be one-fourth of a 65 mg tablet or a one-fourth dose of liquid
- Infants between the age of one month and three years: 32 mg, which would be one-half of a 65 mg tablet or a one-half dose of liquid
- Children between the ages of 3 and 18 years: one 65 mg tablet or one mL solution
- Adults: 130 mg, which could be one 130 mg tablet, two 65 mg tablets, or two mL of liquid
- Breastfeeding mothers: 130 mg
- Children who weigh more than 150 pounds: 130 mg.
The doses described here protect the thyroid gland for 24 hours. A one-time dose will likely be sufficient in most situations. If high levels of radioactivity persist in the environment or food supply, public health officials may recommend daily dosing as outlined above. Newborn infants, pregnant women, and breastfeeding women should be evacuated if radioactivity persists in the environment, and should not receive additional doses of potassium iodide unless other protective measures (such as evacuation, sheltering, and control of the food supply) are unavailable.
Potassium iodide has generally been found to be safe when administered in recommended doses. Higher doses of potassium iodide do not increase protection against radioactive iodine. In adults and children at risk for exposure to radioactive iodine, the overall benefits of potassium iodide far exceed the risks of overdosing. Closely monitoring dose in infants is particularly important, however.6 Administration of potassium iodide to newborns has been associated with changes in thyroid hormone levels, so newborns who receive potassium iodide should have their thyroid function monitored.6 Individuals who are allergic to iodine and those who have certain skin, kidney, or thyroid conditions should consult a physician before using potassium iodide.7
Chernobyl Incident Demonstrates Safety
One of the best evaluations of the safety of potassium iodide use occurred following the Chernobyl nuclear power plant accident in 1986. Some 16 million persons living in nearby Poland were given single doses of potassium iodide as a preventive measure following the accident.8 Researchers investigating the accident found that potassium iodide supplementation reduced the amount of radiation in the thyroid by at least 40%. Furthermore, they found only rare instances of side effects in this population. In general, the side effects associated with the proper use of potassium iodide included mild gastrointestinal symptoms and rashes.
Emergency Preparation with Potassium Iodide
What role does potassium iodide play in radiological emergency planning? Whether radioactive release is from a nuclear power plant accident, a terrorist attack on a nuclear power plant, or from the detonation of a nuclear bomb, potassium iodide plays an important role in emergency preparedness. Please note that potassium iodide is ineffective for other radionuclide exposures such as strontium-90 and cesium-137.
Rapid evacuation is the best way to prevent whole-body exposure to radiation from these sources. Evacuation protects the entire body rather than specific areas of the body. However, when radioactive emergencies occur, rapid evacuation or protective sheltering is not always possible, and this is when access to potassium iodide supplementation becomes so important. In these circumstances, potassium iodide supplementation is an inexpensive, safe, and logical preventive measure.
The United States Nuclear Regulatory Commission has developed a policy that ensures adequate stockpiles of potassium iodide for populations within a 10-mile radius of every nuclear power plant in the United States. In general, government distribution of potassium iodide and emergency preparedness involving its use has been less than ideal. A recent study found that potassium iodide distribution was poor in an area near two nuclear power plants.9 These researchers also found that the New Jersey community in question had highly variable knowledge about how to use potassium iodide prophylactically following a nuclear accident.
The FDA approval of over-the-counter potassium iodide opens the door for individuals and communities to acquire this agent to provide for their own emergency planning. This planning should include knowledge of the proper prophylactic use of potassium iodide among all those concerned with emergency preparedness, including local public health authorities, physicians, emergency personnel, and individuals.
Hopefully you won’t need it any time soon, but it is critical that you stock up a personal supply for future emergency use.
Protecting Yourself in a Nuclear Emergency: What You Need to Know
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2. Barnett DJ, Parker CL, Blodgett DW, Wierzba RK, Links JM. Understanding radiologic and nuclear terrorism as public health threats: preparedness and response perspectives. J Nucl Med. 2006 Oct;47(10):1653-61.
3. Cardis E, Kesminiene A, Ivanov V, et al. Risk of thyroid cancer after exposure to 131I in childhood. J Natl Cancer Inst. 2005 May 18;97(10):724-32.
4. Dayem M, Navarro V, Marsault R, Darcourt J, Lindenthal S, Pourcher T. From the molecular characterization of iodide transporters to the prevention of radioactive iodide exposure. Biochimie. 2006 Nov;88(11):1793-806.
5. Kroizman-Sheiner E, Brickner D, Canfi A, Schwarzfuchs D. Blocking of the thyroid against I-131 following a nuclear disaster. Harefuah. 2005 Jul;144(7):497-501, 526, 525.
6. Available at: http://www.fda.gov/cder/guidance/4825fnl.htm. Accessed July 3, 2007.
7. Available at: http://www.pdrhealth.com/drug_info/nmdrugprofiles/nutsupdrugs/iod_0146.shtml. Accessed July 3, 2007.
8. Becker DV, Zanzonico P. Potassium iodide for thyroid blockade in a reactor accident: administrative policies that govern its use. Thyroid. 1997 Apr;7(2):193-7.
9. Blando J, Robertson C, Pearl K, Dixon C, Valcin M, Bresnitz E. Assessment of potassium iodide (KI) distribution program among communities within the emergency planning zones (EPZ) of two nuclear power plants. Health Physics. 2007 Feb;92(2 Suppl):S18-26.