The answer is both yes and no. Unfortunately, the answer would really be, in most cases, no. According to the CDC, potassium iodide is great for protecting people against radioactive iodine, which is one of the things released in the Japan nuclear reactor explosion. However, it only protects the thyroid gland. It does not protect the rest of the body.
Here's how it works: after a radiological event, radioactive iodine may be released into the atmosphere. It can then enter a human body by being breathed into the lungs, or being ingested through contaminated food or water. The CDC calls that “internal contamination.” The thyroid gland could be easily damaged by the chemical, as it readily absorbs iodine, but the potassium iodide blocks the radioactive iodine from being taken into the gland.
It should be noted that if a person has hyperthyroid (overactive), frequently they simply give him radioactive iodine to take to "kill" the gland. Thereafter, the patient takes a thyroid supplement for the rest of his or her life.
Howver, potassium iodine cannot protect against radioactive agents, such as cesium, which was also released in the Japanese reactor explosion. It cannot prevent an agent from entering the body and damaging other portions, such as the lungs if ingested via breathing. It cannot reverse the damage caused by radioactive iodine once it has been done to the thyroid.
In effect, what Japan is doing with their implmentation of a distribution of potassium iodide is protection against radioactive iodine, but that is it. It will be good against thyroid damage, but as an extreme example, you couldn't have save someone from the effects of the radiation from fallout from the Nagasaki or Hiroshima atomic bombs through the use of iodine.
That said, the CDC still has a series of recommendations about the use of potassium iodide (KI):
After a radiologic or nuclear event, local public health or emergency management officials will tell the public if KI or other protective actions are needed. For example, public health officials may advise you to remain in your home, school, or place of work (this is known as “shelter-in-place”) or to evacuate. You may also be told not to eat some foods and not to drink some beverages until a safe supply can be brought in from outside the affected area. Following the instructions given to you by these authorities can lower the amount of radioactive iodine that enters your body and lower the risk of serious injury to your thyroid gland.
The FDA has approved two different forms of KI—tablets and liquid—that people can take by mouth after a nuclear radiation emergency. Tablets come in two strengths, 130 milligram (mg) and 65 mg. The tablets are scored so they may be cut into smaller pieces for lower doses. Each milliliter (mL) of the oral liquid solution contains 65 mg of KI.
According to the FDA, the following doses are appropriate to take after internal contamination with (or likely internal contamination with) radioactive iodine:
- Adults should take 130 mg (one 130 mg tablet OR two 65 mg tablets OR two mL of solution).
- Women who are breastfeeding should take the adult dose of 130 mg.
- Children between 3 and 18 years of age should take 65 mg (one 65 mg tablet OR 1 mL of solution). Children who are adult size (greater than or equal to 150 pounds) should take the full adult dose, regardless of their age.
- Infants and children between 1 month and 3 years of age should take 32 mg (½ of a 65 mg tablet OR ½ mL of solution). This dose is for both nursing and non-nursing infants and children.
- Newborns from birth to 1 month of age should be given 16 mg (¼ of a 65 mg tablet or ¼ mL of solution). This dose is for both nursing and non-nursing newborn infants.
The protective effects of a dose of KI is about 24 hours. KI is available without a prescription, and a pharmacist can sell you KI brands that have been approved by the FDA.
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