Suppose that a nuclear power plant near your home has a problem, and radioactive material is released. The scope of the disaster could be fairly limited, as happened at Three Mile Island, or more extensive, as happened at Fukushima and Chernobyl. In any case, the surrounding population is at risk, to some degree, from radioactive fallout.
One of the radioactive isotopes released by nuclear power plant accidents is radioactive iodine (I-131). This isotope has a half-life of only 8 days, meaning that, after 8 days, 1/2 of the radioactive iodine material has decayed into non-radioactive material (mostly xenon gas). After another 8 days, another half has decayed, reducing the remaining radioactive material to 1/4th of the original amount. Each additional 8-day period reduces the amount of radioactive isotopes remaining by another half: 1/2 x 1/2 x 1/2 …. After a total of 80 days, the radioactive material has progressed through 10 halves, or “one over two to the tenth power” (1/2^10), which is 1/1024th of the original amount. So after 80 days, 99.9% of the radioactive iodine has decayed.
In case of possible exposure to radioactive iodine (I-131), potassium iodide (KI) tablets can be used to reduce your risk of thyroid cancer. After Chernobyl, due to the release of I-131 into the surrounding region, the percentage of thyroid cancer cases, especially in children, skyrocketed. [FDA, Guidance: Potassium Iodide as a Thyroid Blocking Agent in Radiation Emergencies, p. 7.]
KI tablets block the uptake of radioactive iodine by competitive inhibition. The FDA has approved of KI tablets as safe and effective:
FDA: “The effectiveness of KI as a specific blocker of thyroid radioiodine uptake is well established. When administered in the recommended dose, KI is effective in reducing the risk of thyroid cancer in individuals or populations at risk for inhalation or ingestion of radioiodines. KI floods the thyroid with non-radioactive iodine and prevents the uptake of the radioactive molecules, which are subsequently excreted in the urine.” (U.S. FDA, Emergency Preparedness)
So when your body is flooded with non-radioactive iodine, by means of KI tablets, it is less likely to take up the small amount of radioactive iodine that might get into your system.
The dosage recommendations by the U.S. FDA are here: in PDF format (p. 9)
However, I’ll give a quick summary. All quotes below are from that FDA document.
When you take a KI (potassium iodide) supplement, the protective effect lasts only about 24 hours. So you would need to take one dose per day. Dosage amount depends on age and body weight.
FDA: “Adults older than 40 years should not take KI unless public health or emergency management officials say that contamination with a very large dose of radioactive iodine is expected. Adults older than 40 years have the lowest chance of developing thyroid cancer or thyroid injury after contamination with radioactive iodine. They also have a greater chance of having allergic reactions to KI.”
Adults over 40 years of age do not need KI supplements, unless their predicted thyroid exposure is greater than or equal to 500 rads (500 cGy), in which case the dosage is 130 mg of KI once each day. However, a radiation dosage of 500 rads is very high. If your area has such a high radiation level, evacuation is a necessity; tablets will be of limited benefit. So in a typical case of a limited release of radioactive material from a nuclear power plant, adults over 40 don’t need to take KI tablets.
Adults over 18 through 40 years should receive 130 mg of KI once each day.
Adolescents over 12 years through 18 years should receive 65 mg of KI once each day, unless they are approaching adult size (i.e. approaching 70 kg of body weight, which is 154 lbs), in which case they should receive the full adult dose: 130 mg of KI once each day.
Children over 3 years through 12 years should receive 65 mg of KI once each day.
Young children over 1 month through 3 years should receive 32 mg of KI once each day (half of a 65 mg KI tablet).
FDA: “Individuals intolerant of KI at protective doses, and neonates, pregnant and lactating women (in whom repeat administration of KI raises particular safety issues, see below) should be given priority with regard to other protective measures (i.e., sheltering, evacuation, and control of the food supply).”
Infants from birth through 1 month [neonates], as well as pregnant and nursing women, should only take KI on the advice of a physician or government medical authorities. In such a case, they should receive one dose only, and then be evacuated. That single dose for neonates is 16 mg of KI, one time. That single dose for pregnant or nursing women is 130 mg of KI, one time. Only in cases when evacuation is not possible, should they risk taking KI tablets repeatedly, and then only on the advice of a physician or government medical authorities.
FDA: “Neonates ideally should receive the lowest dose (16 mg) of KI. Repeat dosing of KI should be avoided in the neonate to minimize the risk of hypothyroidism during that critical phase of brain development…. Pregnant women should be given KI for their own protection and for that of the fetus, as iodine (whether stable or radioactive) readily crosses the placenta. However, because of the risk of blocking fetal thyroid function with excess stable iodine, repeat dosing with KI of pregnant women should be avoided. Lactating females should be administered KI for their own protection, as for other young adults, and potentially to reduce the radioiodine content of the breast milk, but not as a means to deliver KI to infants, who should get their KI directly. As for direct administration of KI, stable iodine as a component of breast milk may also pose a risk of hypothyroidism in nursing neonates. Therefore, repeat dosing with KI should be avoided in the lactating mother, except during continuing severe contamination. If repeat dosing of the mother is necessary, the nursing neonate should be monitored as recommended above.”
Stocking up on KI
The most expensive KI tablets are those designed specifically for radiation emergencies. These usually come in a foil-pack, with relatively few tablets per box. Fourteen of the 130 mg tablets is enough for two weeks protection for:
one adult (or larger teen)
four infants or toddlers (1 month to 3 years)
As for myself, I live near a nuclear power plant, and I’ve chosen to stock up on the 32.5 mg sized tablets, the inexpensive ones, in a plastic jar. This size tablet (32.5 mg) is easier to administer to children. The 130 mg tablets need to be cut into halves or quarters for children, which can be difficult to do with accuracy. At 32.5 mg, four tablets is one dose for an adult; two tablets is one dose for a child or teen; one tablet is one dose for an infant or toddler (1 month to 3 years). These are not packaged in foil, but they are much less expensive.
For what length of time should you take the pills? It depends on the situation, so follow the instructions of government medical authorities.
Nuclear power plants accidents might also release radioactive strontium (Sr-90) and radioactive cesium (Cs-137), but that is a subject for another post.