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Radioactive and stable iodine

Radioactive and stable iodine: risks and rewards

On March 11, Japan experienced a devastating earthquake followed by a tsunami resulting in catastrophic damage and loss of life. This natural disaster in turn caused a man-made disaster by severely damaging four nuclear reactors with the ongoing release of radioactivity. Of particular concern is iodine (I)-131, the unstable radioactive isotope of iodine.

The Indian Point Nuclear Power Plant on the Hudson River in Buchanan, NY, sits atop the Ramapo fault line, causing concern for some residents in the wake of the Japan disaster.

Normally, stable iodine is an essential element for the thyroid gland to produce thyroid hormone that is required for the optimal development of the human brain. As a result, brain damage from iodine deficiency in the foetus and developing child is the leading cause of preventable mental retardation.

The requirement for iodine in adults and children is about 150 micrograms a day, usually in the form of iodised salt. Pregnant and breastfeeding women require more iodine; the minimum amount for them being 250 micrograms a day. The International Council for Control of Iodine Deficiency Disorders (ICCIDD), along with Unicef, Who and other agencies have been strong advocates of the use of iodised salt.

Significant iodine deficiency occurs in about 2 billion people, or one-third of the global population. As an example of the importance of this micronutrient, administration of iodine to a population living in areas of moderate to severe iodine deficiency results in an average increase of 10 to 13 points in their IQ.

When a nuclear reactor malfunctions, enormous amounts of the radioactive isotope of iodine (I-131) are released into the atmosphere and will be deposited on crops and pastures and can then enter the food chain mainly, but not exclusively, through milk. When taken up by the human thyroid, the I-131 itself produces radiation that damages the gland and strongly increases the risk of developing thyroid cancer. The risk for thyroid cancer is greatest in children. The administration of a large stable iodine dose of 130 milligrams (mg), which is one thousand times the normal intake, dilutes the I-131 and limits accumulation of the radioactive isotope in the thyroid.

Iodine in the form of potassium iodide (KI), administered within 1-2 hours after internal contamination with I-131, can block more than 90% of the thyroid uptake. Taking KI more than 4 hours after the event provides little protection. In an iodine-sufficient population, the acute administration of iodised salt has little or no beneficial effect. However, the presence of iodine deficiency increases the amount of radioactivity taken up by the thyroid.

ICCIDD recommends adherence to the recommendations provided by the US Centre for Disease Control and Prevention (http://emergency.cdc.gov/radiation/japan/ki.asp).