DEAR DR. BLONZ: I have no thyroid problems, but during a recent lecture on iodine, the presenter described a simple test to determine if you are deficient. It involved buying some iodine antiseptic and painting it inside your forearm or thigh. If you wake up the following day and the iodine is still visible, it indicates your body has sufficient iodine. But if the dark color has faded, it indicates your body is iodine-deficient. I wanted your thoughts. -- H.T., Scottsdale, Arizona
DEAR H.T.: Iodine is an essential trace element needed for thyroid hormones, which are substances that help regulate the metabolism. The daily value for adults is 150 mcg, but it is higher during pregnancy and breastfeeding (more on iodine from the NIH at b.link/chse3n).
Absorbed iodine travels in the blood and gets removed by the thyroid, a butterfly-shaped gland at the front of the neck below the larynx. If the body were chronically iodine-deficient, the thyroid gland would enlarge to do a more efficient job of grabbing iodine from the blood. At this point, a condition known as goiter would have developed, including a noticeable bulge in the lower throat area. Iodine is plentiful in the ocean, but is not well-distributed on land. In the U.S., areas where iodine deficiency was common in the early 1900s -- including the Great Lakes, the Appalachian Mountains and the inland Northwest -- came to be known as the "goiter belt." In the 1920s, as a public health measure, the government encouraged manufacturers to add iodine to table salt -- a move that drastically reduced the incidence of goiter.
On a side note, iodine has a connection to nuclear accidents, which often involve a release of radioactive iodine (radioiodine) into the environment. Radioiodine can be absorbed by the body and destroy cells in the thyroid and elsewhere. An iodine deficiency makes one particularly vulnerable to such damage. While those in an area with a radiation emergency are advised to evacuate, another protection can be to take a potassium iodide supplement, which would satisfy the body's need for iodine and protect the thyroid from that danger.
Today, it's uncommon for anyone eating a varied diet to suffer from an iodine deficiency, especially when iodized salt is used. Food containing iodine is limited to seafoods, crops grown in coastal areas and dairy or meat from animals that graze on feed that's supplemented with iodine.
Now, back to your question. There are established, reliable ways to determine whether your body is iodine-deficient, and the method you describe would not be on that list. The procedure you describe, sometimes called an "iodine patch test," is unreliable. Iodine applied to the skin can be absorbed, and it can happen more rapidly if there is a severe deficiency, but the iodine will also lose its color when it converts to (colorless) iodide, a process that can occur irrespective of the level of iodine in the body. That patch test may work under some circumstances, but it is not considered a reliable indicator of your iodine status.
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