Although severe iodine deficiency was eliminated in the United States nearly a century ago after the introduction of iodized salt, iodine intake has declined in recent decades. “Public health efforts to limit salt intake to decrease cardiovascular risk, in conjunction with increasing use of kosher salt and sea salt (neither of which contain iodine),” may in part be to blame. Not adding salt to foods is a good thing, as sodium is considered the second leading dietary killer in the world (second only to not eating enough fruit), but if you do add table salt, make sure it’s iodized. “It is a myth (often also false advertising) that ‘natural’ sea salt contains significant amounts of iodine.”

Fruits and vegetables provide iodine, but the amounts can vary depending on where it’s grown and how much iodine is in the soil. Because iodine is particularly important for fetal brain development, there’s a recommendation that “all US women who are pregnant, lactating, or even planning a pregnancy should ingest dietary supplements containing 150 mcg of potassium iodide per day,” which I discuss in my video Iodine Supplements Before, During, and After Pregnancy.

Is there evidence they’re not getting enough? We’d like to see urine levels over 150 mcg/L in pregnant women, but in the United States, pregnant women only average about 125 mcg/L. For example, a recent survey in New York City showed only about half of pregnant women were making the cut.

Don’t most pregnant women take prenatal vitamins, though? Only about half of prenatal multivitamins contain any iodine at all, and so only about one in five pregnant women in the United States are following the recommendations of the American Thyroid Association to take a daily iodine supplement, specifically in the form of potassium iodide rather than seaweed, as the levels in seaweed are subject to natural variability. Though the iodine content was as much as 90 percent off in some of the potassium iodide prenatal supplements, the kelp supplements varied even wider, off by as much as 170 percent.

Now, the American Thyroid Association admits it doesn’t have evidence that the current borderline insufficiency levels are leading to undesirable outcomes and so its rationale that all pregnant women take iodine supplements is a bit tenuous. Until such data are available, though, it figures better safe than sorry.

A randomized, placebo-controlled, interventional trial would answer the question once and for all, but the existing evidence for iodine supplementation during pregnancy is so convincing that it would be considered unethical to randomize pregnant women to a placebo.

When it comes to sufficient iodine intake during pregnancy, I’d recommend: Just do it.


Women eating plant-based diets may find this video of special importance: Pregnant Vegans at Risk for Iodine Deficiency.

This isn’t to say sea vegetables aren’t good for you in their own right. See Which Seaweed Is Most Protective Against Breast Cancer?.

For more videos on having a healthy pregnancy, see:

In health,
Michael Greger, M.D.

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