Taking iodine is a protection only against damage to the thyroid gland following exposure to radioactive iodine, which is one of the contaminants to be expected from a reactor accident. It is certainly present in the Fukushima plumes but there are other far more dangerous radionuclides as well.
Taking stable iodine in this way is called "stable iodine prophylaxis". It works by flooding the thyroid gland with stable iodine so that the thyroid cannot take up the radioactive iodine.
Taking iodine is no protection against external irradiation or any type of radioactive pollution other than radio-iodine.
If you live in a place which the plume seems likely to contaminate, and if you have access to potassium iodide or preferably potassium iodate, then use it. After Chernobyl, increases in thyroid cancer were reported in the USA and UK in addition to the well-known increase in the territories nearer to the scene of the disaster.
The UK Health Protection Agency says stable iodine prophylaxis has been demonstrated to have minimal side effects, and there are no medical grounds for restricting the sale of stable iodine tablets to the public. However, UK pharmacists are not allowed to obtain supplies.
These are the recommended daily doses. Don't exceed them.
Equivalent mass of iodine (milligrams(mg))
Potassium iodate (mg)
Potassium iodide (mg) 1
Children aged 3-12 years
Children aged 1 month-under 3 years
Neonates (birth-under 1 month)
15Sources of natural iodine are kelp, onions, seafood, and fruit and vegetables grown in iodine-rich soil. Amounts of iodine in these foods, and in iodised table salt, are too low to provide a protective function in a radiation emergency. However, it's not a bad idea to pay attention to this aspect of diet as long as any of the Fukushima reactors goes on fissioning.
Some posters on the internet give alarming warnings about taking iodine. These are probably based on the historical reluctance of some government authorities to give routine issues of the tablets to people who live near nuclear power stations. One reason for their reluctance is that children may find the tablets and think they are sweets, with nasty side effects (find them on the web). The more cynical are entitled to think that the official reluctance to give out iodine is based on the idea that it would lead the public to conclude that the authorities aren't too sure nuclear power is as safe as they claim. (In any case potassium iodide doesn't store indefinitely - the iodide breaks down to iodine which is an irritant.)
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