Potassium Iodide to Protect the Thyroid from Nuclear Fallout – Reader’s Questions

With recent nuclear power plant crisis in Japan, everyone’s asking about taking potassium iodide.

Since the CDC and FDA offer detailed information, I will not duplicate that information (see references below), but rather focus here on questions readers have asked.  I may add to this post as time goes on, depending on future questions.

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Question from MP: Regarding this article from SurvivalBlog ( http://www.atsdr.cdc.gov/csem/iodine/treatment_management2.html), it indicates Potassium Iodide is not needed for anyone over age 40 if exposed to high levels of radiation since their risk of thyroid cancer is low. Is this true?

Answer: Per the CDC: “Adults older than 40 years should not take KI unless public health or emergency management officials say that contamination with a very large dose of radioactive iodine is expected. Adults older than 40 years have the lowest chance of developing thyroid cancer or thyroid injury after contamination with radioactive iodine. They also have a greater chance of having allergic reactions to KI.”

Doc Cindy adds: The statement is half-true, or at least needs further explanation.  Part of the question here is the amount of (potential) exposure, which you probably won’t know unless a health or government official can tell you.  With a minimal exposure, adults over 40 years of age need not be treated.  With a high dose, they should be treated, however.  In between is not specified, though your supply of KI may determine what you decide to do.  If you have kids and limited KI available, protect them first. One dose is better than none, but if the need for KI exists at all, the need will probably persist for several days.  It makes more sense to protect susceptible children over several days than to treat adults unlikely to suffer with eventual radiation-related thyroid cancer (even though overall thyroid cancer is more common with increasing age.)

However, though the risk of side-effects is increased in these middle-aged and older adults, since the protective effect is primarily from the first dose, and since the CDC advises a single dose for pregnant and nursing women anyway, it seems reasonable for adults to protect themselves with a single immediate dose of potassium iodide, especially since there are no second chances.  Once the damage is done, there’s no going back.  If the iodine is concentrated in the thyroid, it cannot be removed, without removing the entire gland, which is not going to be feasible.  It also makes no sense to treat a person who has inadvertently been exposed for days.  Late treatment is ineffective.

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Question from TQ: Should patients with underlying thyroid disease take potassium iodide to prevent thyroid cancer?

Answer: Per the CDC: “People with thyroid disease (for example, multinodular goiter, Graves’ disease, or autoimmune thyroiditis) may be treated with KI. This should happen under careful supervision of a doctor, especially if dosing lasts for more than a few days.”

Doc Cindy adds: The most common form of thyroid disease in adults in hypothyroidism.  The second article below discusses how hypothyroidism worsens with higher iodine intake.  At least theoretically, ingesting potassium iodide may worsen your underlying thyroid condition in a dose-dependent manner.  Personally, I doubt if a single dose would cause an observable problem in any non-allergic individual.  The patients in the article below (whose TSH levels improved with iodine restriction) only had a TSH of 21.9 to begin with, meaning they were unlikely to have clinical (noticeable) hypothyroid symptoms.

The CDC advice also says the KI should be administered under the supervision of a doctor, meaning frequent and on-going assessment of thyroid function, including blood testing.  Whether such would be available is questionable.  Again, I’d go with my original answer and say a single early dose is advisable.

Click links below for more information

Potassium Iodide, under Emergency Preparedness and Response at http://emergency.cdc.gov/radiation/ki.asp

Effect of Iodine Restriction on Thyroid Function in Patients With Primary Hypothyroidism at http://www.medscape.com/viewarticle/459924

Frequently Asked Questions on Potassium Iodide (KI) at http://www.fda.gov/Drugs/EmergencyPreparedness/BioterrorismandDrugPreparedness/ucm072265.htm