Thyroid cancer a hazard from radioactive iodine emitted by Japan’s failing nuclear power plants


Former Executive Editor, Harvard Health

One of the most abundant substances in the cloud of radioactive steam released by a failing nuclear power plant is iodine-131—a radioactive form of the element, iodine, that is found throughout nature. Iodine-131 poses a special health risk because of its cancer-causing effect on the thyroid gland.

The small, butterfly-shaped thyroid sits just below the voice box. From this perch, it controls how fast every cell in the body changes food into energy. The gland’s main product, thyroid hormone, governs the function of the digestive tract, brain, heart, nerves, muscles, bones, skin, and more.

Iodine is a key ingredient that goes into making thyroid hormone. We get this element from ocean-caught or ocean-farmed fish and shellfish, milk, cheese, yogurt, eggs, and fruits and vegetables grown in iodine-rich soil.

The human body is surprisingly good at absorbing iodine and storing it in the thyroid gland. That’s a problem when iodine-131 is released into the atmosphere. The thyroid stores it as readily as natural, non-radioactive iodine. As iodine-131 builds up in the thyroid gland, it emits bursts of radiation that can damage DNA and other genetic material. Such damage can remove the normal limits to cell growth and division. Unchecked growth of thyroid tissue is thyroid cancer.

Iodine-131 gets into the body several ways. A person can breathe in radioactive steam released by a nuclear power plant. Fallout—radioactive particles that fall out of the atmosphere and settle onto plants, soil, and water—further adds to the burden when a person eats iodine-131 enriched fruits and vegetables or drinks water containing the isotope. Milk is another vehicle—cows that eat grass sprinkled with iodine-131 make milk that contains it.

Following the explosion and meltdown of the nuclear reactor at Chernobyl in 1986, follow-up health studies showed a significant increase in thyroid cancer in the area around Chernobyl, especially among children who were under 10 years old at the time of the explosion and those in utero. Youths may be most affected by iodine-131 because their thyroid glands are still growing and developing. Fortunately, as cancers go, thyroid cancer is one of the least deadly. In the United States, only about 5% of people who develop thyroid cancer die of the disease. (Researchers aren’t yet sure if this applies to radiation-induced thyroid cancer.)

As my colleague Peter Wehrwein describes in a related post, taking potassium iodide pills can help keep iodine-131 from taking up residence in the thyroid gland. The seafood-rich Japanese diet provides an abundance of iodine. Because the thyroid glands of those affected by fallout from the failing nuclear power plants may be “full” of natural iodine, iodine-131 may not be able to get into the gland, giving them natural protection against radiation-induced thyroid cancer.


  1. Conservatories

    That was really a informative article. It is really astonishing to know that a radioactive iodine can cause a threatening disease like cancer. I am glad that you are working together to educate people regarding it. Early diagnosis can save many lives. Appreciative effort 🙂

  2. Anonymous

    Seafood-rich Japanese diet provides an abundance of iodine. I love seafood.

  3. Sumerian

    Interesting that keeping iodine levels high in your diet can protect you from bad iodine-131, very interesting. If anyone is looking to keep your iodine in check naturally, and experience something different. I would recommend eating some kombu.

  4. ade

    great tips, i will try that one
    thank you

  5. Shine

    So iodine-131 is only present in places where there were “nuclear accidents”? It is not normally present in the atmosphere?

  6. remedy

    Great tips from you. They are all work so well to me.
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  7. wafaa

    Sir. How many victims over the world who suffere this desease?

  8. steve

    I don’t know if I should be concerned or not. I try to prevent being around iodine the best I can. As you can tell, I have a personal stake in this matter, having had a thyroid removed because of this disease 🙂 . I’d like to spare others the same fate, if possible.

  9. Anonymous

    This would definitely help not just in Japan’s situation but also from the thyroid itself causes goiter and their hormone functions.

  10. nitro trucks

    my mother have this cancer too…it realy sad looking her got pain
    thanks for article, btw can us cured this cancer?

  11. nitro trucks

    thanks for article, btw can us cured this cancer?

  12. Aji

    Very sad to read all about this. Thanks for the good information and the research on the topic, most people will agree with your blog.

  13. Bobby Hawk

    I find it amazing that doctors and lawyers and politicians and activists all bang the drum when it coms to radiation from nuclear power plant but completely ignore the radiation from EMF’s, which are more common and occur daily. A nuclear power plant failure as a risk is a very low occurrence and as we witnessed from the Japan reactor failure, does not ever result in an exposed core. Further a melt down of a reactor core can be controlled as long as the core has a containment system (Chernobyl did not have a core containment system).
    The likely hood of a nuclear power plant failure is extremely low. So the question remains why the increase of thyroid cancer in women? Since we are not experiencing daily eruptions of nuclear power plant failures, why is the thyroid cancer increasing? The medical industry reports an increase in thyroid cancer in women since the 1970s to have doubled. Additionally they report that women are 4 times more likely to get thyroid cancer than men. So what is the source of increased thyroid cancer in women and why is EMF radiation, emitted from electronic devices, off limits concerning the discovery of the increase in thyroid cancer as well as other cancers? News will ramble all day about the radiation emitted from nuclear power plants which are in failure but say nothing about the radiation emitted by electricity and electrical devices. The question is Why?

  14. crystal x

    Thanks for this, it clearly and concisely explains the function of the thyroid. I am a follicular thyroid cancer survivor and think many people truly do not understand what a major role a healthy thyroid pays in your overall health and well being.

  15. Shawn

    I found a good article on how radiation works that gives some insight on the Japan Nuclear power plant disaster.

    • Bobby Hawk

      The IAEA and NRC are good sources for the actual data being observed during and after the Japan nuclear reactor failure. The data and figures of the release of radioactive contaminants are given in charts and maps. Understanding the measurements and the levels is also provided. Just understand that the measurements are given in MiliSieverts in Japan and the rest of the world. The the USA measures in Milirem’s, so you have to use an equation to convert the two. Its important you understand these exposure levels and which ones place you at risk. Quite possibly the highest risk you will ever experience in your life will be the exposure to radiation as a result of medical equipment. However the fact remains that you need to be aware of your exposure to radiation on an annual basis. Knowing this can assist you with avoiding harmful radiation exposure levels.

  16. Importing To UK

    Nice read!! This article gives me a clearer information about the causes of Thyroid cancer… Thanks for this informative article.

    • Bobby Hawk

      Not exactly as the article does not address EMF radiation and its contribution to thyroid cancers. Until this is known, the cause of thyroid cancer is not resolved.

  17. Tomi

    At least it is one of the least deadly.Well this is a some kind of comfort.

  18. demian

    I hope they are still monitoring hat sre the nuclear plants shooting to the open air.

  19. proppiewp

    Very sad to read all about this. Thanks for the good information and the research on the topic, most people will agree with your blog. Keep up the good work

  20. Asesoria de Imagen

    I hope they are still monitoring hat sre the nuclear plants shooting to the open air. There should be some kind of shell to trap all dangerous substances before they fly away to the atmosphere…

  21. Anonymous

    it is expected that Japan catátrofe leave any sickness in people for generations. Nuclear power seems too dangerous.

    • Bobby Hawk

      Go to the NRC website and the IAEA web site and actually read the millsevert emissions data for these failed nuclear power plants. With 4 plants in complete reactor failure the millisevert readings remained far lower than ever imagined and none of the reactors ever attained core breach (exposed core). The design and the 40 year old containment units held as they should have. Had the people of Chernobyl had a reactor with a core containment then they would have averted the high exposure to radiation which occurred there.

      To damn all nuclear power because of a rare reactor failure is not logical. There are many rectors operating world wide in very safe conditions, providing non-fossel fuel solutions to complex energy needs. The Japanese proved to the world once again that nuclear power, even in the worst of times, can be contained and controlled. The events which took place in Japan in early 2011 will undoubtedly change forever the methods used to avert and contain nuclear power plants. However the truth still remains the containment units held, they did their job and many millions of Japanese are alive today due to those initial designs.

      Is there another power source even more abundant than nuclear which can safely provide electricity for many centuries? The answer is yes. The power source is hydrogen stripped from seawater. The emissions from burning hydrogen fuel are natural and have no effect upon humans. Many naval ships are being equipped with hydrogen reactors and tested as this article is being written.

      The other issue centers around the use of electricity all together. As the studies of EMF radiation and its effects on humans are almost nil. Even if we discover a safe power source the effects of EMF radiation on humans remains. With the cases of thyroid cancer increasing 2 fold over the past 4 decades, its time to get to the business of addressing EMF radiation. Humans are exposed to massive amounts of EMF radiation and the volume is only increasing as the use of electrical devices and demand for electricity rises. Simply dial in an AM radio on your next ride to work and listen to the interference caused by EMF emissions.

  22. Anonymous

    This is a pathetic tragedy for Japanese society due to the tragedy caused by nuclear radiation that occurs. whether the disease caused by radiation is equal to the result of his dangerous mercury waste that occurs in Gold Processing hopefully people affected by the radiation can be overcome with good. Thank you for providing very valuable information for us all.

  23. melissa

    i think people in japan have a strong heart and strong will to prove to the world that they can move through this pain.

  24. Tom

    While the Japanese do eat a lot of seafood, isn’t the ocean and particularly the fish around Japan going to be contaminated with iodine 131 as a result of the meltdown? Will the iodine found naturally in the fish somehow neutralize the iodine 131 from the nuclear plant?

    I also wonder if whether iodine 131 can be neutralized by increasing the ph of foods and drinks like alkaline water. According to Dr. Robert Young, cancer is acidic and can be neutralized by increasing the ph of foods and drinks.

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  26. Anonymous

    it’s a danger to people in Japan. I am extremely worried for you.


    is this dangerous disease ?

  28. namita

    To understand what happened in Japan recently, and at Three Mile Island in the U.S. in 1979, and Chernobyl in the Ukrainian SSR in 1986, you first need to know how a nuclear plant works.

    Nuclear plants contain one or more reactors. The reactor core sits in the center of the reactor. It contains radioactive fuels, uranium or a mix of uranium and plutonium, in pellet form. These are packed in long tubes made of zirconium metal.

  29. David Hastings

    Its sad to learn of the Japan nuclear plant disaster and the long term effects it will have on their people.

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  30. sara

    a very useful and interesting article, thyroid cancer affects only women or also men? what are the symptoms?

  31. Dr. Pat Roberts

    There are also risks associated with taking potassium iodide pills. I also recommend natural sources for iodine whenever possible.
    Thanks for the interesting article.

    [URL removed by moderator]

  32. Anonymous

    Thanks for sharing this article on thyroid cancer. Very Informative

  33. Anthony

    Very informative article on Thyroid cancer. I am helping my close friend related to this and have landed to the right place. I could understand it better now. Your article help me to be more understanding towards my friend.

  34. tugiman

    thanks for sharing this article. medical team now a days used potassium iodine to counter act this iodine that cause thyroid cancer. they said that potassium iodine stabilized the thyroid thus it doesn’t need to absorb more iodine.god luky

  35. Anonymous

    Thanks. I thinks important

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  37. Saman

    ike other kinds of cancer, thyroid cancer refers to the growth of abnormal cells which do not die out but multiply and overwhelm the healthy functioning of body organs. There are various forms of thyroid cancer, depending on where the cancerous cells develop. There are mainly four different types, namely: papillary, follicular, medullary and anaplastic thyroid cancer.
    [URL removed by moderator]

  38. Tiki

    There are four standard cancer treatments: surgery, chemotherapy, radiotherapy, immunotherapy or biological therapy. Clinical trials may be studied as a treatment for cancer to meet certain that suite for different condition. Other people may choose other methods of cancer treatment, which usually is not FDA approved and often outside the United States. When the cancer specialist (Oncologist) diagnosed the cancer, The Oncologist will give you several cancer treatment options. He will recommend the best method based on your type of cancer, stage of cancer, your condition and your age. Ultimately, you are the one who makes decision to choose which treatment you want according to your oncologist’ recommendation.

  39. Tom

    Are the japanese the next victim of Thyroid cancer. We all know what happened? Right?

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  40. Nur Rahmat Wahyuaji

    Nice post 😀


  41. Magazin Intim


  42. Anonymous

    is tonsils are also a part of thyroid problem??
    [URL removed by moderator]

  43. Anonymous

    medical team now a days used potassium iodine to counter act this iodine that cause thyroid cancer. they said that potassium iodine stabilized the thyroid thus it doesn’t need to absorb more iodine.
    [URL removed by moderator]

  44. Cadouri

    My mother in law had thyroid cancer and this had end her life, because the information that can helped her was not available , is this fair ????

  45. Magazin Intim

    For those of us in North America, I don’t think it is necessary to rush down shop intim to the drugstore for potassium pills

  46. Miguel

    Poor people in Japan, they have to suffer the effects of radioactive iodine, I hope everything is resolved soon . [URL removed by moderator]

  47. Fernando

    thanks for sharing this article. medical team now a days used potassium iodine to counter act this iodine that cause thyroid cancer. they said that potassium iodine stabilized the thyroid thus it doesn’t need to absorb more iodine.

  48. Marc Azada

    This blog is one way of helping disclosing informative information that may help prevent thyroid cancer or at least gives us an understanding of the illness.

  49. Anonymous

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  50. cancer gastrico

    This is a very informative article. Thank you for sharing this. I never thought what disadvantage this nuclear power plants could do to us. In relation to what had happened to Japan, is there a possibility of greater risk of thyroid cancer to the northern part of Japan?

  51. umpan-mancing-ikan-mas

    good article, but i’m affraid about the effect of radioactive..but you help us with your article..nice information.

  52. Mafidul Arefin

    Thanks for the nice post! Very informative and interesting!

  53. Travels

    Simply wish to say your article is as astounding. The clarity to your post is just nice and i could think you are an expert on this subject. Fine together with your permission let me to clutch your feed to stay up to date with imminent post. Thanks one million and please keep up the gratifying work.

  54. spirulina

    I wonder if spirulina imported from Japan could be contaminated with iodine? I have heard that Janpan have very strong food quality control but who knows how it really is?

  55. david carter

    put aside the health issues – I’m sure as the years pass there will be huge amounts of health issues that surface in connection with the 2 n plants. What I dont understand is, how on earth such an advanced country could be stupid enough to build n plants on the East Coast of Japan where they know a massive fault line exists?


    [URL removed by moderator]

    • Jack Gamble

      Japan is a small, and relatively resource-less country with very few open spaces suitable to renewable energy. Nuclear power was and still is a no-brainer for them.

      As far as health effects go, we’re now four months after the accident and the worst human health affect has been a sunburn to the legs of three workers who went sloshing around in water in the basement of Unit 2.

      Given the measures taken by the Japanese to evacuate and teh distribution of KI pills, I wouldn’t be surprised if there is no health impact, although there will be no shortage of politically motivated people who will produce junk studies claiming millions of deaths.

  56. Aminosaeuren

    Thanks for the explanation with the half life. But how dangerous is Xenon 131 then, or does that do no harm? Another question: I read articles on a German site on this and it seems that vitamin intake can help keeping direct effects under control. is that true?

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  58. DrSmart

    Radiation exposure of the head and neck is associated with thyroid cancer, particularly when administered in low doses at a young age.

    Certain characteristics which may indicate that a nodule is cancerous include a nodule that is “cold” on radioactive iodine scan.

    Other risk factors for developing nodules include a lack of iodine in the diet, which can cause thyroid enlargement, family history of benign thyroid nodules, and pre-existing thyroid disease (e.g. Hashimoto’s thyroiditis).

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  59. L

    I also had my thyroid removed because of a malignant tumor on one lobe – I’m curious about the effects of this radiation fallout on people who’ve already been dosed with RAI-131. Ideally there should be no uptake if there are no thyroid cells remaining but what if there are remnants of thyroid cells or cancer? Would the rate of recurrence be higher?

  60. Warren Phelps

    Thanks for the information. My wife is a thyroid cancer survivor and she took it out 3 years ago. We are considering relocation to Tokyo, Japan, and wondering if there’s anything to be alerted. She regularly takes pill now. Plus, we have 5 year-old boy, and we are not sure living in Tokyo will be a good idea. Many thanks in advance!

  61. WordSorter

    Thanks for this blog — I’m a thyroid cancer survivor myself and am keeping close tabs on this particular situation.

    Do you know of any groups/endocrinologists/anyone else who might be thinking about doing a study among those living within a particular radius of the Dai-Ichi reactor?

    I ask because it might be interesting to compare the incidence of thyroid cancer among the Japanese (with their iodine-rich diets) and those of the Ukrainian children who lived within the radius of the Chernobyl reactor. It could also provide some good information about how to PREVENT thyroid cancer.

    As you can tell, I have a personal stake in this matter, having had a thyroid removed because of this disease :-). I’d like to spare others the same fate, if possible.

    Thanks so much for your reply.

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  64. H Marie Hicks

    If you are highly alergic to iodine, what (if any) affect can japan radiation have on a person living on west coast?

    • Jack Gamble

      If your allergic to Iodine, than weather it’s radioactive or not is irrelevant. As he said, Iodine is Iodine. The body does not discriminate isotopes.

  65. Ray

    If that is so…what are the chances it is raining something I am allergic to. Should I remain indoors? Or would it be the same as the amount that comes from rocks, or is that a different radiation?

    I hate to panic , but the bits of Iodine 131 they have found over the states in the atmosphere, I don’t know if I should be concerned or not. I try to prevent being around iodine the best I can, now it may be raining down.

    Thanks again for your help!

    • Jack Gamble

      Get close enough to any hospital that does radiology, and any patient who has had the treatment in the last month, and you will find higher concentrations there than what they’re reporting in California.

  66. Ray

    If I am allergic to Iodine, would that mean I would be allergic to iodine-131?

  67. Alex

    Is there any information about the minimal amount of radioactive iodine that will cause a cancer in human body?

    News media mentioned “short therm negative effect on health” bad failed to mention what the negative effects are.

    Thank you for your response.

    • Jack Gamble

      It depends on the individual. Kids are far more susceptible. Anywhere beyond 20 miles away from the source and you won’t get any significant dose.

  68. Joan Peterson

    For those of us in North America, I don’t think it is necessary to rush down to the drugstore for potassium pills. I lived in Germany during the Chernoybl explosion and radiation in Germany is still high is some areas. High enough that food can not be consumed from certain areas. But I never had potassium and I am fine 25 years later. So one must judge if the risk is high enough to take potassium. Don’t panic here in North America.
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    • Peter G.

      Potassium iodide pills are most beneficial for the younger crowd. Their thyroids are growing and will absorb radioactive iodine which can cause cancer decades later. If you are older, you do not need to take potassium iodide. You will be dead of old age before the radioactive iodine can cause cancer.

  69. Moshe Sharon

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  70. Ahn Wan

    Extra iodine perhaps , maybe , hard to tell, can make autoimmune thyroiditis worse

  71. Ahn Wan

    people with thyroid disorders really have to speak to their doctor before taking extra iodine.
    That said, many mult-vitamins contain iodine. Some kid gummi bears have iodine. Regular iodized table salt has iodine. Getting your iodine from seafood and ionized table salt will protect your thyroid as well as potassium iodine will.

  72. Leslie

    I have low T3. My doctor already gave me Thyroid Vitamins. My question is, how can your thyroid affect your auto-immune system?

    • Jack Gamble

      The other way around in my case, I have Grave’s Disease (my autoimmune drove my thyroid overactive). Interestingly enough, I-131 was the treatment. I was given a pill with 18.5 millicuries of it.

      PS – I work at a nuclear power plant. It was more than 50 days before I could get into the plant after the treatment because I was so radioactive that I would set off the alarms on the radiation monitors, but they let me walk right out the door of the hospital that first day. 50 days is more than 6 half lives later, so there was plenty of radiation dose to be had standing next to me that first day.

  73. Ben Prusinski

    I did some research and natural food sources such as kelp, spirulina, seaweed, and rosemary offer some protection against the effects of radioactive Iodine damage. What are your thoughts on using natural foods and herbs to protect against radiation damage versus potasium iodine (KI) which is sold out now due to wide spread fear and panic in the USA?

    • Avatar
      P.J. Skerrett

      Ben — It beats me why people in the US are hoarding potassium iodide tablets. From what I understand, even the Japanese aren’t doing this. It seems much more orderly there, despite the triple tragedies. Plants that grow in the sea (kelp, spirulina, etc.) do contain iodine and could, in theory, help the body reject radioactive iodine-131. The problem with these sources is that the amount of iodine is highly variable, so you don’t know how much to eat. The advantage of a supplement is that you know how much potassium iodide is in each tablet.

  74. Donna

    Thanks for this, it clearly and concisely explains the function of the thyroid. I am a follicular thyroid cancer survivor and think many people truly do not understand what a major role a healthy thyroid pays in your overall health and well being.

  75. Carol Dunn

    Is it correct that Iodine-131 decays in only 8 days?

    • Avatar
      P.J. Skerrett

      Carol — Good question. The half life of iodine-131 is 8 days. That means if you start with 100 grams of iodine-131, eight days later you will have 50 grams of iodine-131 and 50 grams of stable (nonradioactive) xenon-131. After 80 days, you’d have just under one-tenth of a gram of iodine-131 and almost 99.9 grams of xenon-131.

  76. I. A. Kangiwa

    I personally salute the author of such a wonderful piece… KEEP IT UP!

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