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Iodine and your thyroid

Iodine is one of the most important nutrients you need to keep your thyroid working well — and it has a major effect on your entire body. That’s why when you have an iodine deficiency, you’ll feel sluggish overall. Plus you’ll experience a wide range of symptoms throughout your body that are related to a low thyroid function, such as fatigue, sensitivity to cold and unexplained weight gain.top iodine foods seafood asparagus iodized sea salt

Most of us may only think of iodine as an added ingredient in table salt, and not as a key mineral we need for our health. While iodine deficiency is certainly not common, it does exist, especially for certain women. For example, women of childbearing age (20-39) in the US had the lowest urine iodine levels of any other age group, according to a 2012 CDC report. It’s important to consider what effect your iodine level could be having on your thyroid, as well as understand that too much iodine – especially all at once – can also cause problems.

Are you sure that you’re getting the right amount of iodine your thyroid needs to do its job and for you to feel your best? Here’s a closer look at why iodine is important for your thyroid, how to know if you’re getting enough (or too much) iodine and what foods are good sources of iodine.

Why is iodine important for your thyroid?

Iodine is a critical element needed to make the essential thyroid hormones that circulate in your body. These hormones – known as T4 (thyroxine) and the more active T3 (triiodothyronine) – ensure healthy signaling between your thyroid, brain and body to regulate your energy, weight, cell metabolism and much more. Unfortunately, the feedback loops between the thyroid and the brain can easily be disrupted when you aren’t getting enough of specific nutrients like iodine, selenium, tyrosine and B vitamins.

Even though iodine is so important to so many of your body’s functions, your body doesn’t make it. You need to make sure you’re getting adequate amounts of iodine from your daily diet, along with supplements when needed, so that your thyroid has the most basic building-blocks to make its key hormones.

Good sources of iodine in your diet

Your thyroid only needs tiny amounts of iodine on a daily basis, so looking at your food choices is a good place to start for boosting your iodine intake. Some of the top food options to add to your everyday diet include:

Top food choices for iodine include:

  • Sea vegetables (such as kelp, dulse, hijiki, nori, arame, wakame and kombu)
  • Seafood (such as clams, shrimp, haddock, oysters, salmon and sardines)
  • Iodized sea salt

Secondary food sources for iodine include:

  • Eggs
  • Asparagus
  • Lima beans
  • Mushrooms
  • Spinach
  • Sesame seeds
  • Summer squash
  • Swiss chard
  • Garlic
  • Dairy products
  • Onions
  • Radishes
  • Watercress

When it comes to the amount of iodine that you’re getting from food, it’s important to remember that even iodized salt is not as high in iodine as you may think. Plus, with many women now watching their salt intake, you may not be getting as much iodine in your daily diet as you did in the past.

In addition to iodine, selenium is another important mineral you need for good thyroid health. Selenium helps the body to recycle iodine. If you have low levels of selenium along with low levels of iodine, it is more likely to lead to a thyroid imbalance.

You can read more about the needed nutrients for your thyroid and the top foods that contain them in our articles Vitamins and supplements for thyroid health and What to eat to support your thyroid reviewed by Dr. Mary James, ND.

How much iodine do you need?

In the US, the recommended daily allowance (RDA) for iodine for adults is 150 mcg/day and 290 mcg/day for lactating women. More and more researchers are saying that increasing the RDA would greatly benefit breast, thyroid and nervous system health in women and infants.

The current RDA is well below the US Food and Nutrition Board’s “upper limit of safety” for iodine (UL = 1100 mcg), which is even lower in Europe (UL = 600 mcg), where iodine deficiency is more common. In Japan, however, where diets include lots of iodine, consumption is about 25 times more than the median intake here.

You can get too much iodine

You can also experience thyroid health issues from too much iodine. Iodine-induced hyperthyroidism (overproduction of thyroid hormones) or iodine-induced hypothyroidism can both occur when people who are already iodine-deficient are given too much iodine, too quickly. Take care when starting with iodine supplements, slowly bringing levels up rather than overloading right up front. You may want to consult with your healthcare practitioner.

Should you get your iodine levels tested?

If you think you could be suffering from low thyroid, subclinical hypothyroidism or even hypothyroidism (inadequate production of thyroid hormones) it makes sense to have your iodine levels tested. This is especially important if you don’t eat many iodine-containing foods or use iodized sea salt. As we learn more about how iodine functions in the body, we’re seeing more and more connections between diet, environment and the rise of thyroid health problems in women.

Here’s a simple test for iodine deficiency that you can safely do at home:

  • Dip a clean ball of cotton in inexpensive red-tinged USP tincture of iodine from any drugstore.
  • Paint a 2-inch circle of tincture of iodine on soft skin tissue, such as the inner arm or thigh.
  • Wait to see what happens: if the yellow-orange stain takes more than 6 hours to disappear, you are likely to be iodine-replete. If the stain is absorbed quickly (within 1-3 hours), your body may need a higher iodine intake.
  • Depending on your results, you may want to talk with your healthcare practitioner for the more detailed 24-hour iodine/iodide loading test.

Reference: Skidmore, B. 2007

You may also want to consider additional testing if you think you have a thyroid issue. Talk with your doctor about getting a full thyroid hormone panel, along with testing for your iodine, selenium and vitamin D levels.

If you have low thyroid symptoms, the more you know about thyroid nutrition, the better.

Last Updated: March 24, 2023
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