How Does Potassium Iodide (KI) Pill Provide Anti-Radiation Protection?

Going back to June 23, 1966, the New England Journal of Medicine. Vol. 274 on Page 1442 states:

"The thyroid gland is especially vulnerable to atomic injury since radioactive isotopes of iodine are a major component of fallout."

Cresson H. Kearny, the author of Nuclear War Survival Skills, Original Edition Published September, 1979, by Oak Ridge National Laboratory, a Facility of the U.S. Department of Energy (Updated and Expanded 1987 Edition) states on page 111:

"There is no medicine that will effectively prevent nuclear radiations from damaging the human body cells that they strike.However, a salt of the elements potassium and iodine, taken orally even in very small quantities 1/2 hour to 1 day before radioactive iodines are swallowed or inhaled, prevents about 99% of the damage to the thyroid gland that otherwise would result. The thyroid gland readily absorbs both non-radioactive and radioactive iodine, and normally it retains much of this element in either or both forms. When ordinary, non-radioactive iodine is made available in the blood for absorption by the thyroid gland before any radioactive iodine is made available, the gland will absorb and retain so much that it becomes saturated with non-radioactive iodine. When saturated, the thyroid can absorb only about l% as much additional iodine, including radioactive forms that later may become available in the blood: then it is said to be blocked. (Excess iodine in the blood is rapidly eliminated by the action of the kidneys.)"

The Nuclear Regulatory Commission (NRC) stated July 1, 1998 in USE OF POTASSIUM IODIDE IN EMERGENCY RESPONSE:

"Potassium iodide, if taken in time, blocks the thyroid gland's uptake of radioactive iodine and thus could help prevent thyroid cancers and other diseases that might otherwise be caused by exposure to airborne radioactive iodine that could be dispersed in a nuclear accident."

Federal Register. Vol. 43 Friday, December 15, 1978, states in Potassium Iodide as a Thyroid Blocking Agent in a Radiation Emergency:

"Almost complete (greater than 90%) blocking of peak radioactive iodine uptake by the thyroid gland can be obtained by the oral administration of ... iodide ..."

National Council on Radiation Protection and Measurements. NCRP Report NO. 55. Protection of the Thyroid Gland in the Event of Releases of Radioiodine. August, 1979, Page 32:

"A major protective action to be considered after a serious accident at a nuclear power facility involving the release of radioiodine is the use of stable iodide as a thyroid blocking agent to prevent thyroid uptake of radioiodines."

The recently updated (1999) World Health Organization (WHO) Guidelines for Iodine Prophylaxis following Nuclear Accidents states:

"Stable iodine administered before, or promptly after, intake of radioactive iodine can block or reduce the accumulation of radioactive iodine in the thyroid."

And, finally, the recently (November, 2001) released FDA document Potassium Iodide as a Thyroid Blocking Agent in Radiation Emergencies states:

"The effectiveness of KI as a specific blocker of thyroid radioiodine uptake is well established (Il'in LA, et al., 1972) as are the doses necessary for blocking uptake. As such, it is reasonable to conclude that KI will likewise be effective in reducing the risk of thyroid cancer in individuals or populations at risk for inhalation or ingestion of radioiodines."