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Iodine, a trace element, is one of the most important—and most overlooked—minerals your body needs. In the early 1900s, iodine deficiency was a big problem in the United States, but the issue receded after iodine was added to most table salts and used to make dairy and baking products. Today, most Americans still get enough, but some experts fear iodine deficiency is on the rise again, especially among women, and it too often goes undiagnosed. 

What iodine does

When you don’t get enough iodine from foods such as fish, sea vegetables, and even iodized table salt, you can become iodine deficient. If you’re low in iodine, your body can’t make enough thyroid hormone, which regulates metabolism, body temperature, muscle building, and more, says Elizabeth N. Pearce, MD, an endocrinologist at Boston University School of Medicine. “This may lead to hypothyroidism or thyroid gland enlargement, also known as goiter, and can cause fatigue, weight gain, and constipation,” she says.

Iodine deficiency is especially dangerous for pregnant and breastfeeding women. “A mom’s inadequate iodine levels can lead to lower IQ, mental retardation, and even irreversible brain damage in a developing child,” says Pearce. “The problem is, [iodine deficiency] is really tough to detect,” says Elizabeth Large, ND, of Gordon Medical Associates in Santa Rosa, California. “There’s no direct test for it, and often symptoms aren’t noticeable. Or if they are, it’s usually low energy, brain fog, or dry mouth or skin, which can also be caused by so many other issues.” 

Why you may be low

“The recent push to reduce salt intake may be contributing to iodine deficiency among women,” Pearce says. “They are less likely to add salt to their food or use it when cooking. And even though 75 per- cent of Americans’ salt intake comes from processed foods, those aren’t made with iodized salt.” 

Pearce says women today also eat a lot less dairy, which contains iodine. Plus, “iodine content in fruits and vegetables is hugely variable, depending on the region and soil in which they are grown,” she says. “Seafood is generally a good source of iodine, but amounts are difficult to quantify. Generally, saltwater seafood contains more iodine than freshwater; iodine also varies by where the fish were caught and in what season.”

Common chemicals may also cheat you out of iodine. Constant exposure to fluoride from tap water, chlorine from swimming pools, and bromide from plastic food containers, pesticide-sprayed produce, and flame retardant–coated furniture all compete with iodine in the body, says Large. “The cells that need it the most—thyroid, breast, brain, and skin cells—soak up these chemicals instead of iodine.”