Could an Iodine Deficiency Be Messing With Your Thyroid?

Iodine is a trace element found in soil and seawater and many foods including milk, eggs, and fish. It’s crucial because your body uses it to make thyroid hormone. If you don’t get enough iodine in your diet, you can’t make enough thyroid hormone to keep your body running normally, and could develop hypothyroidism. Iodine deficiency is rare in the United States thanks to the introduction of iodized salt back in the 1920s. However, if you’re avoiding salt, dairy, or gluten in your diet—or if you’re pregnant or nursing—you may be at risk. “Symptoms include fertility issues, weight gain, feeling cold all the time, and constipation—people with hypothyroidism really don’t feel good,” says endocrinologist Romy Block, MD, a clinical assistant professor at the University of Chicago Pritzker School of Medicine and co-author of The Vitamin Solution. Read on to find out more about the causes and symptoms of an iodine deficiency—and how to prevent it.

Most adults need only 150 micrograms (mcg) of iodine a day and get enough through their diets since it’s found in common foods like milk, cheese, eggs, some bread and fish, as well as in iodized salt. “Deficiency is more of an issue worldwide, in developing countries,” Dr. Block says. (Read more about the best and worst foods for your thyroid.) Still, some groups are at risk for inadequate iodine intake.

Pregnant women require nearly 50% more iodine (220 mcg a day) than the average adult, and women who are nursing need even more (290 mcg), making both groups vulnerable to deficiency. Severe deficiency in pregnant women is linked to miscarriages and preterm delivery—plus it can cause congenital abnormalities and developmental problems in babies, especially in terms of cognitive function. “Be sure your prenatal vitamin contains at least 150 mcg and take it every single day,” says Mark Moyad, MD, director of preventive and alternative medicine at University of Michigan Medical School and author of The Supplement Handbook. Think of iodine the same way you would folic acid during pregnancy—it’s as important, he says.

“Most people need 150 mcg of iodine a day and, to put things into perspective, a glass of milk has about 56,” says Marina Chaparro, RDN, a spokesperson for the Academy of Nutrition and Dietetics. Iodine is in all dairy products, such as cheese, yogurt, ice cream, and butter. An egg has 25 mcg, while a couple of slices of enriched bread have about 45 mcg. Fish such as cod, tuna and shrimp are iodine-rich. And a sheet of seaweed can have more than 2,000 mcg—which is very high, so don’t eat it every day.

Since dairy and grains are common sources of iodine, anyone cutting these food groups may be prone to deficiency, Chaparro says. Using iodized salt and taking a multivitamin containing iodine can make up for a lack of the element in your diet.

“Even if you use sea, Himalayan, or kosher salts—which are not fortified—for certain recipes, make sure you have some iodized salt in your home for general purposes,” Chaparro says. A ½ teaspoon of iodized salt nearly covers the daily requirement for most people. Keep in mind that although many processed and packaged foods contain salt, it’s not usually fortified salt, unless iodized salt is listed in the ingredient list.

When you’re not getting enough iodine, your thyroid—a butterfly-shaped gland below your Adam’s apple—gets bigger as it tries to churn out enough thyroid hormone. Before iodized salt became available, the Great Lake, Appalachian, and Northwestern regions of the United States were known as the “goiter belt” since the neck bumps were so common there.

“Never take an individual iodine supplement or seaweed or kelp pills unless instructed by a doctor to address a known deficiency,” Dr. Moyad says. Many contain more than the recommended daily amounts for iodine and, as a general rule, less is more when it comes to this element. “It’s very easy to overshoot with iodine and get too much,” he says. That can lead to an overactive thyroid (hyperthyroidism) and serious problems like an irregular heartbeat, which can lead to heart failure, strokes and even permanent heart issues, Dr. Block says.

There’s a blood test to check iodine levels—but it’s not accurate, Dr. Block says. So doctors will occasionally do a 24-hour urine check, which is pretty much what it sounds like: “You have to collect your urine in a huge bucket for 24 hours,” she says. “It’s such a pain we don’t do it very often!”