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.

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.

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:

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.