In the past couple of days, as many of us around the world began thinking seriously about the fallout from the damaged nuclear reactors at Fukushima, Japan, I've gotten lots of questions about potassium iodide pills—"Why do people take them?", "How do they work?", "Should my family take them?"

I've spoken with several health physicists—researchers at American universities and at the Mayo Clinic—and I think that I can now answer these questions well enough to post something to BoingBoing. This is a scary, nerve-wracking topic for a lot of people, so I'm not going to bury the information down in a narrative. We'll just get right to the point. In fact, I think that I can clear up most of the confusion by answering four questions.

What are potassium iodide pills?

Basically, potassium iodide is just a specific kind of salt. Nothing fancy. The same stuff is often put into table salt as a way to get iodine into the diets of people who don't eat much naturally iodine-containing food. Iodine, itself, is an element that's important to the human body. Without it, the thyroid gland can't make certain hormones. If you don't eat enough iodine, especially as a kid, you'll end up with goiters, fatigue, depression—and worse. Thanks to iodized salt (and diverse diets), those of us who live in industrialized nations don't have to think about whether we're getting enough iodine. And, thus, we don't think too much about potassium iodide. Until there's a risk of radioactive fallout.

How do potassium iodide pills protect against radiation?

Elements come in two forms: Stable and radioactive, the latter of which are prone to breaking apart, shooting out particles that can damage cells and DNA. There's good ol' stable iodine—the stuff that keeps our bodies functioning properly. And there's radioactive iodine—which is dangerous.

Radioactive iodine is dangerous precisely because, within the human body, it does the same thing that stable iodine does. It goes straight to the thyroid gland.

Once there, radioactive iodine can damage cells and DNA and increases the risk of thyroid cancer. But, there's a catch. The thyroid can only hold so much iodine at a time. Once the shelves are full, any new iodine that shows up is simply excreted back out of the body until the supply needs to be restocked again.

That's where potassium iodide pills come in. If radioactive iodine is present, you can prevent it from getting into your thyroid gland by having the gland already full of stable, safe iodine—the kind found in potassium iodide pills. Because radioactive iodine has a short half-life—by this Saturday, March 19, half of all the radioactive iodine released by the reactors at Fukushima will be gone—affected people don't have to take potassium iodide pills forever. Just long enough for the radioactive iodine to break apart and vanish.

Key takeaway from this part: Potassium iodide pills will only protect against the effects of radioactive iodine in the thyroid. There's other radioisotopes being released by the Fukushima reactors, and potassium iodide can't do anything about them.

What are the risks of taking potassium iodide pills?

There are risks. The big one: You might be allergic to potassium iodide pills. This is particularly likely if you are already allergic to shellfish. The allergic reactions could be life threatening, and there's not really a good way to know whether you'll be allergic to the pills until you try one.

But there's another risk, too. There's not an unlimited supply of potassium iodide pills. If people living in places unaffected by radioactive iodine buy up lots of potassium iodide pills, it means there are fewer of those pills available for the people who really need them. That's why the Union of Concerned Scientists recently put out a press release asking Americans to refrain from buying—or, worse, stockpiling—supplies of potassium iodide pills. People in Japan need them. Which brings us to the final question:

Will radioactive fallout from Fukushima reach the West Coast of the United States?

The answer depends on what you mean. If you mean, "Will radioactive fallout from Japan reach the West Coast in quantities that could increase the risk of cancer for me and my family?" Then the answer is, "No."

The risks of exposure to radiation are dependent on the dose. As it travels across the Pacific Ocean, the concentrated radioactive fallout that leaves Fukushima will become diluted—some will fall out into the ocean, some will drift away on the breeze, some of the isotopes—including radioactive iodine—will even break apart, becoming something else, something not dangerous.

By the time any of the radioactive isotopes reach American shores, the fallout will be so dilute that radiation will have dropped well below the levels that cause detectable increases in the risk of cancer. There will not be a reason for Americans to worry about their health. This is according to Kelly Classic, radiation physicist at the Mayo Clinic; Kimberlee Kearfott, health physicist at the University of Michigan; Ralf Sudowe, health physicist at the University of Nevada Las Vegas; Kathryn A. Higley, health physicist at Oregon State University; Jason T. Harris, health physicist at Idaho State University and, if you read the link above, The Union of Concerned Scientists.

It will be possible to detect radiation from Fukushima in the United States. But that's because the tools we have for detecting radiation are incredibly sensitive. We can spot radiation at levels far lower than those that can actually increase our risk of cancer. Frankly, that's a good thing. It means we can see problems before they build into something serious. It means we can accurately measure dangerous levels of radiation without having to get scientists too close to the radiation source. And, it will mean that we will be able to see very low levels of radiation from Fukushima in the United States, even though the risk from that radiation will be something we can shrug off.

I know this doesn't answer all of your questions, but I hope it helps. I'll be back tomorrow with more information on issues like what happens to radioisotopes that get inside your body, how Fukushima will affect the food chain, why it's mostly OK for radioisotopes to fall into the Pacific Ocean.

EDIT: Charles Q. Choi, a science journalist who is currently reporting from Chernobyl, spotted a quick fact that I forgot to mention. Based on the available evidence, thyroid cancer caused by exposure to radioactive iodine seems to be a problem primarily for children, rather than adults.

Image: Some rights reserved by ark