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Potassium Iodide

December 2004

By Jon VanZile

LE Magazine December 2004
Potassium Iodide
Protecting Yourself In a Nuclear Emergency
By Jon VanZile

It is our collective nightmare as a nation, a threat that could cause wholesale disruptions and produce mass casualties: a nuclear emergency within US borders.

This scenario is a very real and very dangerous possibility. For example, terrorists could use a so-called “dirty bomb” to render uninhabitable an area of several blocks. These devices consist of a conventional explosive rigged to spew radioactive material that is readily available from sources such as universities and hospitals. Terrorists could attack one of America’s more than 100 nuclear power plants. Just imagine if the September 11 attackers had chosen to fly their hijacked jets into three or four nuclear power plants instead of buildings that stood as symbols of national political and economic might. Perhaps worst of all, a terrorist group, perhaps aided by a hostile state, could get its hands on an actual nuclear weapon.

Each of these scenarios presents a different health challenge, but each is gravely serious and potentially lethal on a large scale. A rapid response would be required from our public health infrastructure—a response that might be beyond our reach.

“There need to be plans in place,” says Dana Best, MD, MPH, an attending physician at Children’s National Medical Center in Washington, DC. “We need to beef up our public health infrastructure so it can do its job, which is to protect us from tornadoes, hurricanes, and nuclear weapons.”

During a nuclear emergency, mass evacuations would be necessary—most likely in congested, urban areas where they could easily lead to chaos. As a second option, sheltering would be necessary to protect people from radiation exposure. This, too, would require mobilization on a massive, untested scale.

Since September 11, 2001, the federal government has struggled to update its emergency plans. Agencies such as the Department of Homeland Security, in conjunction with the Federal Emergency Management Agency and the Nuclear Regulatory Commission (NRC), have studied the issue and made recommendations to keep people safe. Fortunately, one of these recommendations is simple, effective, and widely available to anyone interested, not just government workers or people living in the shadow of a nuclear reactor.

The protection is a simple pill of potassium iodide, which contains the same form of iodine used in table salt. It has been shown in multiple studies—and in real-life experience—to safely protect people, especially children, against one dangerous side effect of radiation exposure: the development of thyroid cancer.1,2 Because of this powerful protective effect, the Department of Homeland Security, the FDA, the NRC, the American Academy of Pediatrics, and the World Health Organization have all endorsed the distribution and use of potassium iodide.

A 2003 policy statement issued by the American Academy of Pediatrics, coauthored by Dr. Best, was very clear on the matter: “Potassium iodide is of proven value for thyroid protection but must be given before, or soon after, exposure to radioiodines, requiring its placement in homes, schools, and childcare centers.”1

The Biology of Radiation
In the simplest terms, radiation is energy given off in waves or small particles of matter from unstable atoms. Even at low doses, radiation can penetrate the body and cause cellular damage that results in cancer many years later. At higher doses, radiation can cause severe hematopoietic syndrome, attacking the body’s red and white blood cells. This syndrome can cause death in 8 to 50 days.1

The severity of radiation sickness directly correlates to the degree and length of exposure, and the kind of radiation involved. (For a more detailed description of radioactive substances and how radioactivity is measured, see the sidebar entitled “Understanding Radioactivity.”) Radiation also affects cells in different ways, depending on their rate of division and level of specialization. The most sensitive cells are lymphoid, while the least sensitive are bone marrow and nervous system cells.1

One form of radiation, known as radioiodine, is particularly dangerous to the thyroid gland. Radioiodine is a common byproduct of nuclear power generation. When inhaled, radioiodine is rapidly absorbed by the thyroid gland, where it has a number of harmful effects. It may cause benign tumors, thyroid cancer, or, at high doses, hypothyroidism caused by destruction of the thyroid gland.1,3

Potassium iodide works by flooding the thyroid gland with easily available iodine and, if taken at the right time, preventing or completely blocking the uptake of radioactive iodine.3


Radiation is energy given off in the form of waves or small particles of matter. People are regularly exposed to all different kinds of radiation—from the sun, x-rays taken at the dentist’s office, and innumerable other sources.

Scientists distinguish between “radiation” as energy and “radioactivity,” which is a characteristic of a substance that gives off radiation. They also distinguish between “electromagnetic radiation,” which has no mass and includes sunlight and x-rays, and “particle radiation,” which is emitted as unstable atoms release tiny particles. All radioactive metals emit particles as they try to decay to a more stable form.

Uranium, for instance, emits particle radiation as it tries to decay to a more stable form. It takes uranium 238, one common form of natural uranium, about 4.5 billion years to decay into thorium, another radioactive metal that itself decays in 14 billion years into radium, which decays in about 1,600 years into lead. The time it takes for a radioactive element to decay into its next form is called its “half life.”

Radioactivity is measured by how many “disintegration events” take place per second. In the metric system, one becquerel is one decay per second. Alternatively, the radiation emission of a radionucleotide is also measured in curries. One currie is equivalent to 37 billion disintegrations per second.

The most dangerous form of radiation energy is known as “ionizing radiation,” which has enough energy to break chemical bonds in living organisms. At high enough levels, this energy can create spontaneous DNA mutations, increased production of free radicals, or disruption of basic cell structure. The five forms of ionizing radiation are alpha particles, beta particles, neutrons, gamma rays, and x-rays.

  • Alpha particles are extremely heavy molecules consisting of two protons and two neutrons. They have a limited ability to penetrate skin or clothing, but can be ingested. Radon emits alpha particles.
  • Beta particles are subatomic particles ejected from the nucleus of some radioactive atoms. They are equivalent to electrons. They can be inhaled or can penetrate the skin more easily than alpha particles. Beta particles come from radionuclides used in medicine (such as xenon) or are created as byproducts of nuclear reactors. Radioiodine is a beta particle.
  • Neutrons are powerful but rare particles that are emitted only after a nuclear detonation. They are highly destructive to living tissue.
  • Gamma rays are electromagnetic rays that are emitted from radioactive materials such as cesium or cobalt, or after a nuclear detonation. They are easily able to penetrate tissue and cells.
  • X-rays are also part of the electromagnetic spectrum. They are unlikely to be encountered during a nuclear emergency.

There are two systems for measuring radiation dosage. The older system uses rads (radiation absorbed dose). One rad is produced when one gram of material absorbs an erg of energy (an erg is a very small unit of energy). In the metric system, rads are replaced by grays, with one gray being equal to 100 rads. The rad or gray is the amount of energy absorbed by a tissue or substance.

To calculate the biological effect of radiation, or the dose equivalent, scientists multiply the amount of energy absorbed in rads or grays by a variable called the quality factor, or QF. The QF takes into account the different degrees of biological damage produced by equal amounts of different types of radiation. For x-rays, gamma rays, and most beta particles, the QF equals one. Alpha radiation has a QF of 20, while the QF for neutrons ranges from 2 to 11.

The rem (roentgen equivalent in man) is the product of the amount of energy absorbed (in rads or grays) times the efficiency of radiation in producing biological damage (the QF). The metric system uses units called sieverts, with one sievert equal to 100 rems.

Doses above 100 rems, or one sievert, have been shown to damage red and white blood cells, causing the hematopoietic effect. Dosages above 1,000 rems cause cells lining the digestive tract to die and bacteria to invade the bloodstream, a condition known as the gastrointestinal effect. A dose of several thousand rems can lead to brain injury and death within hours.