To amuse myself on Monday, I looked on Google Trends for “potassium iodide” just to see if it was a popular search term. I was right- it was. In fact, right now its #8 for the US. As of Monday morning, CVS.com, amazon.com, and all my local drug store and alternative health stores are completely sold out of the stuff, and a quick scan of the news suggests this is a nationwide trend (here too.) Why? Because if you believe the internet chatter, potassium iodide protects against “radiation.”
Let’s make one thing clear- it doesn’t, or rather it does only under drastically specific conditions. What potassium iodide does, is to ensure that the body has an adequate supply of iodine from a known, non-radioactive source. Why is this important? Because otherwise, you have an increased risk of contamination by fallout. No, not the video game.
Fallout is radioactive dust- the airborne particles created by a nuclear explosion or the release of nuclear materials; a nasty cocktail of radioactive elements with varying half-lives and effects. Which elements are present in fallout depends a lot on the precipitating incident, and often the exact composition can’t be predicted and must be measured post-facto in the field.
Fallout particles have varied fates. Some decay into stable (non-radioactive) particles quickly, and become essentially harmless. Others are so mildly radioactive that, while they do technically decay, it happens so slowly that they contribute little to the background radiation. Some are radioactive enough to decay energetically, but have long enough half-lives to persist in the environment as hazards to plant, animal, and microbial life; among these is iodine-131, produced by tellurium and uranium decay. I-131 has a half-life of about 8 days, which means that every 8 days, half of the iodine decays into beta particles, gamma waves, and xenon-131, a stable gas with limited ability to interact with other atoms. This fits unpleasantly into the danger window- I-131 is radioactive enough to cause health problems, but not radioactive enough to disappear before living creatures have been exposed.
Adding to the hazards of I-131 is the fact that unlike most fallout components, iodine is a vital human nutrient that is concentrated in one particular organ, in this case the thyroid. Production of normal thyroid hormones depends on a supply of dietary iodide, which most Americans obtain by eating seafood or iodized salt. In the absence of iodine, hormone precursors accumulate in the thyroid, unable to complete the reactions to be secreted into the blood, and form a goiter. If the body is low in iodine, it will aggressively absorb iodine and iodide from food sources, and if those sources have been contaminated by fallout, the body will then concentrate the radioactive iodine in the thyroid- and radiation near a gland is a recipe for cancer.
The theory behind taking potassium iodide tablets is that if the body is not deficient in iodine, it will not waste the metabolic energy absorbing and concentrating iodine from food or water (including radioactive iodine from fallout,) and will thus be spared a large dose of radiation directly into a fairly vulnerable tissue. Some radioactive iodide will still be absorbed, but it will be diluted by the non-radioactive iodide in the supplement.
Potassium iodide does not protect against radiation, however. Actual radiation (those alpha, beta and gamma “particles” you learned about in physics class) doesn’t give a rip whether you’re topped up with iodine or not. Those workers in the Fukushima plant are being exposed to biohazards we can’t avoid without sheets of lead or other barriers. Potassium iodide does not protect against non-iodine fallout either: many other isotopes, including strontium-90 (which accumulates in bones) and cesium-137 (which accumulates in muscle and has a gamma-emitting half-life of 30 years) are as dangerous or more dangerous than iodine-131. Other fallout isotopes may not concentrate in body tissues, but if they accumulate in the environment (in a dust filter, for instance) they can emit radiation and pose a hazard to anyone working nearby.
Does this mean there’s no point to the tablets? Sadly, epidemiologists are fond of marginal improvements and there is data suggesting that iodine deficiency was a risk factor for children exposed to fallout after the Chernobyl incident who developed thyroid cancer later in life. This is probably no comfort to the families of those children who developed cancer despite having an adequate dietary intake of iodine. Such is the cost of massive disasters. And the nuclear power people are quite correctly pointing out that the number of people who die every year of coal related illness (think heavy metal poisoning, arsenic, asthma, groundwater contamination) is greater than the total number who will die of what I think we can call the worst nuclear disaster since 1986. Physicians are always uncomfortable managing the symptoms of a disease if the cause is left unaddressed. Despite the panic at the drugstore, I doubt many “symptoms” will crop up on this side of the Atlantic this time, but perhaps this would be an excellent moment to review our… shall we say lifestyle risk factors?
[Edited to add: growing up, I found the “nuclear survival manuals” in the public library to be somewhat baffling; now I have the information to understand them more fully. An important point to remember is that fallout is toxic dust- many of the techniques people use to avoid exposure to other toxic dusts, like pollen, coal dust, asbestos or pesticides also help against fallout. Staying indoors, filtering air, wearing particulate masks, or misting down dust clouds with water can reduce the risk of inhaling or otherwse absorbing fallout particles; this is why the Japanese government is asking people near the exclusion zone to “shelter in place.” Those class-A bunny suits don’t actually protect against radiation (well, not against beta, neutron or gamma radiation) but they do keep the radioactive dust off the plant-workers’ skin. This distinction is also why radiation panic in the inland US is so curious to me- dust clouds, even big ones, rarely reach all the way across the pacific. If they did, we would all have a much higher annual death rate from the Asian Brown Cloud than from radiation incidents, even outliers like this one. Oh well, as a friend reminds me, we’ll know for sure soon enough.]