Protection against radiation has become a much-discussed topic following the earthquake and tsunami-related problems at the six nuclear reactors in Fukushima, Japan. We wanted to provide you with reliable and beneficial information on the potential protective effects of diet in this context. As such, we looked to the latest scientific research and included it with the foundation of our knowledge on this subject. We hope that this information serves to be beneficial to you.
When a radioactive material like uranium-235 or uranium-238 undergoes fission in a nuclear reactor, one of the fission products is a radioactive form of iodine-131 (I-131). I-131 can bind onto iodine receptors in the thyroid gland and cause many types of possible dysfunction, including the development of thyroid cancer.
Following the nuclear disaster at Chernobyl in 1986 in the northern Ukraine, many healthcare and regulatory commissions became interested in the use of potassium iodide (KI) supplements as a way of helping protect the thyroid from radiation release. The principle here was very simple: by flooding the thyroid with non-radioactive iodine (iodine in the KI supplements, which would be provided in its stable I-127 form), all of the receptors for iodine in the thyroid would be filled with I-127 and there would be no opportunity for radioactive I-131 to bind onto receptors.
The KI supplementation idea was determined to work, but it was also found to be very sensitive to certain conditions. For example, taking a KI supplement four days prior to radiation exposure was found to be much less effective than taking the supplement within two days of exposure. Protection was also found to be dependent on dose. Doses of KI between 30-200 milligrams were evaluated, and approximately 30-35 milligrams were determined to be the starting point for effective dosage. Toward the lower end of the range, protective effects were found to last for approximately 24 hours, and toward the middle of the range (around 130 milligrams) for approximately 48 hours.
The levels of iodine in KI supplements are far greater than the amount of iodine that can be obtained from a normal, healthy diet. One quarter cup of a sea vegetable like kelp - one of the world's richest foods in terms of iodine content - provides an average of approximately 400 micrograms of iodine, or about 1/87th of the amount found in a 35 milligram KI tablet. We have not seen any research that shows effective flooding of the thyroid and protection against radiation at levels of iodine intake this low. For this reason, a focus on dietary iodine as an emergency step to provide short-term protection against I-131 does not make sense to us.
What does make sense, however, and what is backed by research findings, is the ability of long-term dietary sufficiency of iodine to protect against future potential exposures to I-131. Studies of patients exposed to radiation following the 1986 explosion at the Chernobyl Nuclear Power Plant and other radiation studies have found greater uptake of I-131 with dietary deficiency of iodine and less uptake when dietary iodine was plentiful. In fact, even soil concentrations of iodine (the source of iodine in land plants) have been found to correlate with I-131 uptake - where soil concentrations of iodine are high, there is a lower risk of radiation-induced thyroid cancer, and where soil concentrations are low, there is an increased risk. All of these results point to the importance of optimal iodine nourishment in protection against radiation-induced thyroid cancer over the long run (even though we cannot find evidence of short-term, emergency protection from I-131 exposure through diet).
While sea vegetables top our list of foods concentrated in iodine, dairy products like yogurt and cheese are also very good sources of this mineral, as are eggs and strawberries. Of course, iodized salt is also a concentrated source of iodine (and the number one source in the U.S. diet). You can find out more about iodine on our website in our "Essential Nutrients" section under the "Iodine" heading.
If you are considering greater intake of sea vegetables to improve your iodine nourishment, we also recommend that you pay close attention to the quality of the sea vegetables you are purchasing. Following is additional information you may find helpful for selecting high-quality sea vegetables.
Sea vegetables have been a topic of ongoing debate and research concern involving heavy metals. In the world of marine biology and marine ecology, sea vegetables are widely recognized as plants with an excellent ability to take up minerals from the water and hold onto these minerals in their cells. This ability makes sea vegetables a rich source of many wonderful minerals, including magnesium, calcium, iron, and iodine. However, in waters that have become polluted with heavy metal elements - including arsenic, lead, and cadmium - sea vegetables can also act like a sponge in absorbing these unwanted contaminants. Some marine ecologists actually use sea vegetables as a kind of "biomonitor" to determine levels of heavy metal pollution in bodies of water.
Among all of the heavy metals, arsenic appears to be most problematic when it comes to sea vegetable toxicity risk. Virtually all types of sea vegetables have been determined to contain traces of arsenic. These types include arame, hijiki, kombu, nori, and wakame. Among all types of sea vegetable, however, hijiki stands out as being particularly high-risk when it comes to arsenic exposure. During the period 2000-2005, government-related agencies in England, New Zealand, and Canada issued public health recommendations advising against consumption of hijiki sea vegetable unless verified as containing very low levels of inorganic arsenic. Based on these reports, we recommend avoidance of hijiki as a sea vegetable unless available in the form of certified organic hijiki.
Unfortunately, the availability of certified organic sea vegetables remains compromised by the status of aquaculture regulations at the National Organics Program at the U.S. Department of Agriculture (USDA). As of late fall 2011, even though recommendations for organic seafood had officially been voted on and adopted by the National Organics Standards Board within the USDA, these recommendations had not yet been added to the National List or implemented into law - giving consumers no option for USDA-certified organic sea vegetables or seafood of any kind. Some sea vegetables are available in the U.S. that have been certified as organic by organizations other than the USDA (including organizations in other countries), and those products can be a good choice.
Further complicating the picture, however, is the difference between wild-harvested versus farmed sea vegetables. Some certified organic sea vegetables have been farmed in a process that's usually referred to as "aquaculture" or "mariculture" and that involves a closely monitored, contained-water environment for the sea vegetables. Other certified organic sea vegetables have been wild-harvest, but typically in regions where ocean waters are better protected against contaminants. We believe that in both cases (farmed or wild-harvested), you're likely to get a lower level of contaminants like arsenic (or no arsenic contamination whatsoever) by selecting certified organic hijiki (or any other sea vegetable). However, from a sustainability perspective, some people may greatly prefer wild-harvested to farmed sea vegetables, even if certified organic.
Finally, in order to assure yourself of no arsenic contamination whatsoever, you'll need to find a certified organic product that reports lab testing on the packaging and specifically indicates an arsenic-free status.
The levels of arsenic found in other types of sea vegetable have been relatively small. The U.S. Environmental Protection Agency (EPA) has set an oral Reference Dose (RfD) for arsenic exposure of 0.3 micrograms per kilogram of body weight per day. For a person weighing 154 pounds, that amount translates into 21 micrograms of arsenic. In research on sea vegetables, sea vegetable-containing supplements (like kelp supplements) are better studied than fresh sea vegetables, so it can be helpful to look at sea vegetable supplement data when trying to evaluate the arsenic risk from sea vegetables. In multiple research studies, the amount of arsenic present in one tablespoon (10 grams) of kelp has averaged about 4-5 micrograms, or approximately 20-25% of the RfD. While this level of arsenic intake is well beneath the EPA's threshold for daily oral intake, it may still be an amount that some persons wish to avoid. Your only guarantee for avoiding this arsenic exposure is to find and purchase sea vegetables that have been specifically tested for arsenic content and report arsenic-free contents on the packaging. As described earlier, you are also much more likely to get a low level of arsenic exposure (or no arsenic exposure at all) by selecting of certified organic sea vegetables.
You can find more information about sea vegetables on our website in our "WHFoods List" under the "Sea Vegetables" heading.
Amster E, Tiwary A, and Schenker MB. Case report: potential arsenic toxicosis secondary to herbal kelp supplement. Environ Health Perspect. 2007 Apr;115(4):606-8.
Cabrita MT, Vale C and Rauter AP. Halogenated Compounds from Marine Algae. Mar. Drugs 2010, 8, 2301-2317.
Muramatsu Y, Sumiya M, and Ohmomo Y. Iodine-131 and other radionuclides in environmental samples collected from Ibaraki/Japan after the Chernobyl accident. Sci Total Environ. 1987, Dec; 67(2-3):149-58
National Research Council. (2005). Health Risks from Exposure to Low Levels of Ionizing Radiation: BEIR VII Phase 2. Committee to Assess Health Risks from Exposure to Low Levels of Ionizing Radiation, National Research Council. National Academies Press, Washington, D.C.
National Council on Radiation Protection and Measurements (NCRP). Management of Persons Contaminated with Radionuclides. February 12, 2008.
Rabin BM; Shukitt-Hale B; Joseph J; Todd P. Diet as a factor in behavioral radiation protection following exposure to heavy particles. Gravit Space Biol Bull. 2005, Jun; 18(2):71-7.
Van Dolah FM. Marine Algal Toxins: Origins, Health Effects, and Their Increased Occurrence. Health Perspect 1 08 (suppl 1):1 33-141 (2000).
Zanzonico PB and Becker DV. Effects of time of administration and dietary iodine levels on potassium iodide (KI) blockade of thyroid irradiation by I-131 from radioactive fallout. Health Phys 2000; 78:660-667.
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