What Is The Role of Iodine in Thyroid Function?
“Take a dose of seaweed or burnt sea sponge twice a year!” That was the ancient Chinese remedy for goiter. Almost four thousand years ago Chinese medical writings described the troublesome swelling of the neck we know as goiter and noted the remedy which had somehow been arrived at through trial and error. Of course Chinese physicians had no idea why it worked, but work it did. Later Hippocrates and Galen gave the same recommendation and by the 12th century the treatment was taught in the School of Salerno, one of the first formal medical schools. Finally, in 1820, Jean Francois Coindet showed that the active principle of the burnt sponge remedy was iodine and demonstrated that goiters decreased in size when an alcoholic tincture of iodine was administered. By the middle 1800s it had become clear that the incidence of goiter varied geographically and that the critical feature was the iodine content of the food that was consumed. Crops grown near the sea had sufficient iodine, but people who subsisted on food grown inland had a high incidence of goiter. Eventually the addition of iodine to salt solved the problem.
The role of iodine began to be clarified in 1896 when it was shown to be present in the thyroid gland. Finally in 1914 Calvin Kendall isolated thyroxin, a thyroid hormone which had four iodine atoms incorporated into its molecular structure. This hormone turned out to be extremely important; it regulated metabolism, as well as kidney and brain function. A lack of thyroxin in babies dooms them to cretinism, marked by severe mental and physical retardation. In adults, an underactive thyroid causes weight gain, mental slowness, depressions and fatigue. And what is the connection to goiter? If there is not enough iodine in the diet, the thyroid gland works overtime to extract as much as possible from the bloodstream and increases in size. But not all thyroid problems are related to iodine deficiency. In the case of Hashimoto’s disease, for example, the thyroid is unable to synthesize thyroxin even if adequate iodine is available. Thyroxin is also lacking if the thyroid has been surgically removed, or partially destroyed by treatment with radioactive iodine to treat an overactive gland. Luckily, there is a solution. In the early 1900s desiccated animal thyroid extracts were used to treat an underactive thyroid but then in 1926 thyroxin was synthesized in the lab by biochemist Charles Harington, making possible the treatment of thyroid problems with a standardized drug. Today, synthetic thyroxine, best known as Synthroid, is one of the most common prescribed medications and allows thyroid patients to lead normal lives. Well, not exactly normal. Some patients complain that they don’t feel quite right and lack energy with Synthroid. And there may be a reason for this. Thyroxine, once released from the thyroid has one of its iodine atoms removed by an enzyme and is converted into a more potent hormone, known as T3. Some researchers believe that an oral combination of thyroxine and T3 is the way to go, but the jury is still out on that one. In any case, we have come a long way since the ancient Chinese recommended burning sponges to treat goiter.