Ask the Doctors: Hypothyroidism often not due to low iodine levels

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Q: I take medication daily for hypothyroidism and borderline high blood pressure. My question is: Do I benefit from iodide in table salt or should I buy plain salt for cooking?

A: Your question highlights how different Western diets are from those in other parts of the world, where iodine deficiency is a significant issue. (For this column, we'll focus on the element "iodine," but "iodide" is the safely ingestible form of it.) That deficiency is due to inadequate dietary intake of iodine, which is found in fish, seafood, kelp, vegetables grown in iodine-rich soil, dairy products — and salt.

Although sea salt also contains a small amount of iodine, many table salt brands in the United States contain much more. That's because both Europe and the U.S. have encouraged the fortification of salt (and some other foods) to maintain adequate iodine intake in the population. Because of those efforts, launched in the U.S. in 1924, we've reduced health problems linked to low iodine intake. That's not to say mild iodine deficiency can't been found, especially with more people consuming unfortified salt, just that it's rare.

In any case, iodine is necessary for the formation of thyroid hormone. With low levels of iodine — a condition known as hypothyroidism — the levels of the thyroid hormones T4 and T3 drop. In trying to produce more thyroid hormone, the thyroid gland enlarges; the externally visible swelling is called a goiter. Low thyroid levels can be risky during pregnancy, especially in the first 12 weeks, when the mother's thyroid hormone is necessary for the development of the fetal nervous system. Severe iodine deficiency in pregnant women can lead to their child's intellectual disability, deafness, inability to walk appropriately and muscle spasms. Prenatal vitamins often contain potassium iodide to prevent iodine deficiency. But it is also important that pregnant women not take too much iodine because this may suppress the fetus's ability to produce thyroid hormone on its own.

As for whether you should consume iodized salt for additional boosting of your thyroid, I wouldn't worry too much about salt's impact on your thyroid levels. Although I'm not certain as to the cause of your hypothyroidism, the most likely explanation — autoimmune thyroiditis — is not due to low iodine levels. In this country, hypothyroidism due to low iodine intake is rare. Rather, you have low thyroid levels for other reasons.

I'm not suggesting you consume copious amounts of salt. Because of your high blood pressure, you should be careful with your intake. Reducing salt consumption has been shown to lower blood pressure in those with abnormally high intake. Instead of salt as a source of iodine, I would recommend increasing your intake of fish, seafood and seaweed snacks. You can also get iodine from fortified breads, cereals and waters.

Overall, the recommended minimal intake of iodine for a non-pregnant adult is 150 micrograms per day; for pregnant women, the recommendation is 220 to 250 micrograms. The average intake in the United States is between 240 and 300 micrograms.

But whatever you do, monitor your blood pressure with changes in your salt intake — and, for good measure, keep an eye on your thyroid levels. If your doctor is concerned about your iodine levels, a urine test can measure it.

Robert Ashley, M.D., is an internist and assistant professor of medicine at the University of California, Los Angeles. Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095. Owing to the volume of mail, personal replies cannot be provided.

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