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Why take iodine?
Dr. Joe Schwarcz looks at our evolving understanding and use of iodine, from its discovery in the early 1800s to its use after the Japan earthquake.
Dr. Joe Schwarcz is Director of McGill University's Office for Science and Society, which is dedicated to demystifying science for the public, the media and students. He is a bestselling author of books such as An Apple a Day, Brain Fuel, and Science, Sense & Nonsense.
Back in the early 1800s, the production of potassium nitrate (saltpetre), an essential component of gunpowder, was a booming industry. The potassium required was isolated from the ashes that remained after burning seaweed ' a messy business.
One day in 1811, the seaweed tank in Bernard Courtois’ saltpetre factory in Paris needed a thorough cleaning and he decided that sulphuric acid was the right chemical for the job.
Within minutes, Courtois was amazed to see the room fill with violet fumes that later deposited on surfaces and formed crystals. He didn’t know it, but he had discovered iodine. It was the French chemist Louis-Joseph Gay-Lussac who identified the crystals as a new element and named it “iode” from the Greek for violet.
Making the thyroid connection
Seaweed is a source of the iodide ion, which in Courtois’ lucky accident was oxidized to iodine by the sulphuric acid. This incident struck a chord with Dr. Jean-François Coindet, a Swiss physician who was familiar with the traditional use of sea sponge ashes to treat the swelling in the neck caused by an enlarged thyroid gland, known as a “goitre.” Could it be, he wondered, that sea sponges, like seaweed, contained iodide, and that this was the therapeutic ingredient?
Coindet went on to successfully treat goitrous patients with iodine, although he had no understanding of why this worked. Finally, in 1896, German chemist Eugene Baumann discovered that iodine concentrated in the thyroid gland. He suggested that the gland’s enlargement was due to its frantic attempt to sequester as much iodine as possible when supplies were inadequate.
Now it made sense why people living near the sea rarely suffered from goitre. The seabed contains soluble iodide salts that wash into the water and concentrate in plants and animals, which are eaten by people. Iodide from the ocean also finds its way into coastal soil and from there into crops. Inland, the crops and the animals that feed on them contain very little iodine, which is why until the early part of the 20th century, the American Midwest was known as the Goiter Belt.
Putting iodine to work
The role of iodine was clearly identified in 1914 when thyroid hormone was isolated and shown to contain the element. In 1924, to remedy the problem of low iodine intake, Michigan began to experiment with adding sodium iodide to salt. And the rest, as they say, is history. Iodized salt would become our first “functional food.”
Iodine's connection to the thyroid also interested Dr. Saul Hertz, who had joined the Thyroid Clinic and Metabolism Laboratory at Massachusetts General Hospital in 1931. But his focus was on Graves disease, a condition in which the thyroid gland becomes overactive and produces too much hormone.
Since the thyroid concentrates iodine, Dr. Hertz wondered whether administration of small amounts of radioactive iodine might partially destroy the thyroid and reduce its activity. By 1946, he had shown that iodine-131 was an effective treatment for hyperthyroidism and to this day it remains the standard therapy for Graves' disease. Radioiodine therapy is also used in cases of thyroid cancer. The rapidly multiplying cancer cells can be destroyed by radiation.
Protecting against radiation
But radiation is a double-edged sword. The gamma rays and beta particles emitted by iodine-131 can also disrupt the structure of DNA and cause cancer. This is a major concern with any nuclear power plant accident since radioactive iodide is one of the products of the uranium fission process used to generate electricity. If accidentally released, it can be inhaled or ingested from contaminated vegetation, dairy products or meat.
How can scientists measure radiation in the body?
Although radiation exposure from a nuclear accident is a rare event, radiation in the body is nothing unusual. “We live in a sea of radiation,” says Dr. Gary H. Kramer of Health Canada. See photos of the detectors that scientists use to measure radiation in the body.
One way to prevent the accumulation of radioactive iodide in the thyroid is to saturate the gland with the non-radioactive version. This is why potassium iodide tablets are distributed to people who live near nuclear power plants. Should there be an accident, they would be advised to take an appropriate dose (130 mg per day for an adult, half as much for a child) until the risk has passed.
The dangers of radioactive iodide exposure, particularly in children, were dramatically demonstrated in 1986 in the Ukraine after the Chernobyl accident. Within four years there was a huge increase in thyroid cancer in children in the areas covered by the radioactive plume. Poland, where potassium iodide tablets were immediately distributed to some 11 million children and 7 million adults after the accident, serves as a remarkable contrast to the Ukraine situation. Virtually no increase in thyroid cancer was observed, clearly demonstrating the protective effect of potassium iodide.
After the Fukushima accident in Japan in March 2011, potassium iodide pills were also distributed to the population in the immediate area. Because it takes years for thyroid cancer to develop, the effectiveness of this action will not be known for some time.
But some panicked people who lived nowhere near the accident site also decided to take potassium iodide pills. While the risk from this unnecessary iodine is small, it is not zero. Excess iodine can exacerbate an underlying hyperthyroid condition ' and in rare cases can cause skin rashes and abdominal discomfort. Furthermore, taking potassium iodide pills over an extended period can cause the thyroid gland to shut down, resulting in hypothyroidism.
Given the distance from the accident in Japan, there was absolutely no need for anyone in North America to take potassium iodide pills. That was almost as silly as the iodine fetish in the 1920s, when some took to wearing bottles of iodine around their necks to protect against developing goitre.
To give even more perspective, the amount of radiation that reached North America from Japan was roughly one one-hundred-thousandth of the exposure one would get on an overseas round-trip flight. That certainly does not warrant taking potassium iodide supplements. But for people living in the vicinity of a nuclear reactor, keeping a supply of potassium iodide on hand is not a bad idea. The probability of an accident is very small, but not zero.
ISSN 1927-0275 = Dimensions (Ottawa. Online)