Here’s What You Need to Know About the Thyroid-Iodine Connection

Mercey Livingston
Medically Reviewed
July 9, 2021

It may be small, but your thyroid is a mighty organ that is responsible for many important functions that can make a huge difference in your health. Metabolism, hormones, digestion, brain, and so much more are all affected by how well (or not) the thyroid is functioning. When the thyroid is not working well, you may feel pretty miserable. Thyroid disorders are common, affecting 20 million Americans every year, and even more common in women (1 in 8 women will have a thyroid disorder at some point in life). And iodine is a huge player in thyroid dysfunction.

Holistic health’s impact on the thyroid

“When thyroid hormone levels are off, the consequences can feel devastating for individuals, like an extreme overall sluggishness, slow metabolism, and weight gain despite doing everything ‘right’,” says Caroline Hoeffgen, a health coach with Parsley Health . Symptoms can range from severe fatigue , brain fog , hair loss, to more severe PMS, mood swings, and more. “The most common thyroid issues are autoimmune driven like Hashimoto’s thyroiditis and Graves disease,” says Hoeffgen. Not all thyroid conditions are autoimmune driven, but a large percentage of conditions are driven by Hashimoto’s thyroiditis, which is an autoimmune disease . Although the exact number of people who have Hashimoto’s is unknown, 5 in 100 Americans have hypothyroidism , which is commonly caused by Hashimoto’s.

“Luckily, we are now understanding more and more that most thyroid disease is a process and not a permanent condition,” says Hoeffgen. Thyroid conditions can be managed through medical intervention, but also diet and lifestyle are major factors for treatment and ultimately success in managing conditions and reducing symptoms. Lifestyle plays a huge role in thyroid health, with diet and nutrition at the forefront : “Diet is the single biggest controllable risk factor of thyroid disease that has been identified,” says Hoeffgen. “We now know that thyroid disease is much more reversible than previously thought. Diet plays the biggest role in that reversal,” says Hoeffgen.

When it comes to thyroid health, nutrition is key since your thyroid needs nutrients like selenium, zinc, iron, and b-vitamins to function well. Diet can also play a role in thyroid disease, which is why when you are diagnosed with a thyroid condition, your doctor and health coach may work with you to modify your diet, and one common food your doctor may recommend removing from your diet is gluten .

“It has been hypothesized that gluten is a cause for thyroid disease through something called molecular mimicry and gut permeability,” says Hoeffgen. In certain cases, especially when autoimmunity is at play, it makes sense to take gluten out of the diet because of this. If there are underlying gut issues and inflammation , or your doctor suspects they may be at play, they may also recommend removing gluten to help prevent further issues.

How the thyroid and iodine are connected

Iodine is essential for the body in the right amounts. Iodine deficiency is commonly cited as a cause of thyroid issues, but what’s lesser known is excess iodine leading to thyroid disease. “Excess iodine is a known and well-studied cause of thyroid disease (both non and autoimmune), and this has been shown in test tubes studies , epidemiological studies , and interventional trials ,” says Hoeffgen.

Why such little attention to this? People having too little iodine had been a huge issue for a long time, explains Hoeffgen, with goiter being a common issue in the 1800s as well as brain damage in newborns and hypothyroidism. In the 1920s, countries like the U.S. started iodine supplementation , mainly by adding it to table salt. And it helped decrease rates of goiter. “But now we have an overcorrection situation and the U.S. is amongst many other countries classified by WHO as having unsafe exposures,” Hoeffgen says.

So why can this little nutrient you probably don’t think much about have such an impact? Many people actually do fine with excess iodine, but for those that do not, it can contribute to thyroid disease. “Iodine is used almost solely in the thyroid and only for the purpose of making thyroid hormones. What makes this nutrient so unique is unlike most other nutrients where the body can easily get enough without getting too much, the safe range of iodine is far narrower than had been speculated. It is a goldilocks nutrient, we need just the right amount,” explains Hoeffgen. Hoeffgen says that many people are consuming too much iodine and may not even know it.

Foods high in iodine

Since the normal amount of iodine that is recommended for each person can vary, it’s best to discuss your diet with your doctor or health coach to help you understand how much iodine you need or if you should lower your iodine intake. With that, here are some of the most common foods that are high in iodine:

  • Processed food and commercially baked goods: “The amount of iodide in processed foods is not always reported – best to avoid processed foods,” says Kina Khatri, MD a physician at Parsley Health.
  • Dairy
  • Sea vegetables
  • Iodized salts: Hoeffgen recommends swapping this for low iodine options (non-iodized kosher salt or Celtic sea salt).
  • Certain seafood
  • Egg yolks (especially eggs that are not pasture-raised)

Non-food sources of iodine

Should you have your iodine levels tested?

Testing for iodine levels is not always the best option, which is why it’s important to speak to your clinician before overhauling your diet or self-diagnosing a problem. Especially for pregnant and/or lactating women, they should not tinker with their iodine levels on their own—they should be closely monitored as their needs are slightly higher than others.

“There is no best test for iodine levels in an individual,” says Dr. Khatri. Although studies have been done on iodine levels, “The test used to measure iodine levels in populations for research purposes is a 24-hour urine iodine level and creatinine ratio,” she explains, so it’s not a simple diagnostic test. That said, if you do make adjustments to your diet that may impact iodine levels, your clinician can and should be looking at your thyroid hormone levels. “Those on thyroid medication need to be closely monitored by their doctor as their need for medication might shift very quickly,” says Hoeffgen.

How Parsley Health can help

If you want to find the right approach to healing your thyroid or preventing disease, you can work with a doctor and health coach at Parsley to get a custom plan fit for your needs and health history. When it comes to changing your diet, it’s easy to feel overwhelmed but Hoeffgen says your coach will make sure that you start with the easiest and most doable changes, and go from there. “We really go into detail and see what we can shift right away,” says Hoeffgen.

According to Hoeffgen, oftentimes when people remove gluten from the diet or follow popular diets for autoimmune thyroid diseases like AIP, paleo , or vegan diets, they remove large sources of iodine (dairy, processed flour products, eggs) so those can be helpful for many people with thyroid issues. But Hoeffgen says if your doctor identifies iodine as an issue, you may not need to remove entire food groups in order to support and heal the thyroid.

“We want to encourage change where it will move the needle most for patients. Sometimes, focusing on lowering iodine even by a bit can be all that is needed since so many trials have shown reversal of thyroid disease with that being the only factor of change,” she says.

Keep in mind that not everyone with a thyroid issue will need to do the same type of diet or necessarily remove gluten and iodine. Testing your thyroid, tracking your thyroid markers and symptoms, testing other health markers, health history, and going over all of your risk factors can help your health care team get a better picture of your health and overall needs.

Mercey Livingston

Mercey Livingston is a health and wellness writer and certified Integrative Nutrition Health Coach. She is passionate about translating expert and science-based wellness advice into accessible and engaging content. Her work is featured on Well+Good, Women's Health, Business Insider, and among others. When not writing, she enjoys reading, trying out new recipes, and going to new workout classes all over New York City.

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