Iodine Deficiency and Your Thyroid Health

Too little or too much iodine can cause problems

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Iodine is an element that's required for the thyroid gland to produce thyroid hormones, which are secreted into the blood and then carried throughout the body to regulate metabolism and ensure healthy functioning of the heart, brain, and other organs. Since the body does not produce iodine on its own, it needs to come from dietary sources—and striking the right balance is key. Inadequate levels or overconsumption of iodine can lead to or worsen thyroid disease. And while iodine deficiency is a more common cause of thyroid problems in underdeveloped countries, it must be considered in every thyroid patient.

Risks of Iodine Deficiency

Since iodine is needed to make thyroid hormone, diminished levels can lead to hypothyroidism (low thyroid function). Iodine deficiency is also linked to the development of goiter (thyroid enlargement), the condition of which can cause coughing, rapid heart rate, heat intolerance, shortness of breath, throat tightness, and weight gain.

The impact of too little iodine reaches further. Children born to mothers with severe iodine deficiency can suffer from stunted growth, severe and irreversible intellectual disabilities, and problems with movement, speech, and hearing.

Even mild iodine deficiency during pregnancy can lead to subtle intellectual deficits, although many children improve with iodine supplementation.

Fibrocystic breast disease, a benign condition characterized by lumpy, painful breasts mostly in women of reproductive age, is also associated with iodine deficiency.

The World Health Organization (WHO) estimates that two billion people, including 285 million school children, are iodine deficient. Among them, iodine deficiency disorders (IDD) affect some 740 million.

Since the iodization of salt first began in the 1920s, the incidence of IDD in the United States has dropped significantly. To further stem the risks of thyroid disease, the American Thyroid Association (ATA) called for the universal iodization of salt in 2017.

Risks of Excessive Iodine

Given the strong link between iodine and thyroid health, it's reassuring to learn that iodine deficiency is rare in the United States and other developed countries where iodized salt is used.

Indeed, as an International Journal of Molecular Sciences study reported in 2014, iodine excess is currently a more frequent occurrence. And if iodine deficiency isn't the cause of hypothyroidism (as it often isn't), then iodine supplements won't be helpful.

For some people with abnormal thyroid glands, excessive iodine can trigger or worsen hypothyroidism. While initially, you may have more energy, high doses can cause an "iodine crash" that leaves you feeling exhausted and achy within a few days.

That's because high iodine intake can initiate and exacerbate infiltration of the thyroid by lymphocytes, the white blood cells that accumulate due to chronic injury or irritation.

In addition, large amounts of iodine block the thyroid's ability to make thyroid hormones. The conclusion of two studies, one published in 2006 in the New England Journal of Medicine (NEJM), the other in 2014 in the journal Endocrinology and Metabolism, is that more-than-adequate or excessive iodine levels are unsafe and may lead to hypothyroidism and autoimmune thyroiditis (Hashimoto's thyroiditis, chronic lymphocytic thyroiditis), especially for people with recurring thyroid disease.

People predisposed to Hashimoto's (as evidenced by high levels of autoimmune antibodies) are at greater risk of hypothyroidism simply by increasing their intake of iodine beyond adequate levels.

The NEJM study showed that the risk is highest in people with a TSH of 2 or greater (considered the middle to upper end of normal range) who consume an average of 400 micrograms (mcg) of iodine per day.

Moreover, the overconsumption of iodine has been shown to increase the risk of thyroid papillary carcinoma, the most common type of thyroid cancer in the United States.

How Much Iodine You Need

According to the Food and Nutrition Board of the National Academies (formerly the National Academy of Science), the recommended dietary allowance (RDA) for iodine in the United States ranges anywhere from 90 mcg per day for toddlers to 150 mcg for teens and adults.

Considering that one cup of plain low-fat yogurt contains about 75 mcg, 3 ounces of fish sticks contain about 54 mcg, a cup of cooked pasta contains about 27 mcg, and a quarter teaspoon of iodized salt contains about 71 mcg, that's generally an easy amount for most people to consume.

Pregnant and Breastfeeding Women

The American Thyroid Association recommends that all pregnant and breastfeeding women in the United States and Canada take a prenatal vitamin containing 150 mcg of iodine a day as part of an overall recommended intake of 220 mcg/day and 290 mg/day, respectively.

That said, excess iodine can be particularly dangerous in these women. In a 2012 study published in The Journal of Pediatrics, women who took too much supplemental iodine during pregnancy gave birth to babies that suffered from congenital hypothyroidism, a thyroid deficiency that, if left untreated, can lead to mental, growth, and heart problems.

Do You Really Need Supplements if You Have Thyroid Disease?

Despite all of this, some practitioners are almost knee-jerk in their insistence that anyone with a thyroid problem requires iodine supplementation; alternative practitioners may recommend iodine-containing herbs, like kelp or seaweed.

This can be particularly risky for the reasons mentioned above, but also because iodine supplements can interact with several types of drugs, including anti-thyroid drugs used to treat hyperthyroidism. Taking high doses of iodine with anti-thyroid medications can have an additive effect and could cause hypothyroidism.

You'll want to be very careful about taking iodine unless you and your practitioner have some very strong evidence that you're deficient. This is especially true if you're pregnant or planning to become pregnant.

Diagnosing Iodine Deficiency

Diagnosis of iodine deficiency is difficult because 90 percent of the iodine you ingest is quickly expelled in urine. As such, detectable levels change constantly, making urine-based tests less useful on an individual basis.

The iodine urine test is used almost exclusively for statistical purposes to measure iodine values within the community and to pinpoint areas of widespread deficiency. Within this context, iodine deficiency is defined as a median urinary concentration of less than 50 mcg per liter within a population.

Research issued by the National Institutes of Health reveals that iodine levels in the United States are considered sufficient, although they did drop by around 50 percent between the 1970s and early 1990s. Data from 2007 to 2008 has shown that levels have since returned to being sufficient.

From an individual standpoint, iodine deficiency is typically suspected based on the development of goiter, hypothyroidism, or congenital hypothyroidism (low thyroid function at birth).

Risk factors for iodine deficiency include pregnancy, the avoidance of iodized salt, and iodine-poor diets high in goitrogenic foods such as soy, cassava, and cruciferous vegetables such as cabbage, broccoli, and cauliflower.

Goitrogenic foods like soy may impact your body's ability to utilize iodine, sometimes significantly.

Iodine Sources

Again, it's important to remember that in the United States, the risk of iodine deficiency is relatively low. In addition to iodized salt, we tend to get plenty of iodine from the food we eat.

Iodine-rich sources in a balanced diet include:

  • Cod (3 ounces): 99 mcg
  • Plain low-fat yogurt (1 cup): 75 mcg
  • Reduced fat milk (1 cup): 56 mcg
  • White enriched bread (2 slices): 45 mcg
  • Shrimp (3 ounces): 35 mcg
  • Enriched macaroni (1 cup): 27 mcg
  • Egg (1 large): 24 mcg
  • Canned tuna in oil (3 ounces): 17 mcg
  • Dried prunes (5 prunes): 13 mcg
  • Cheddar cheese (1 ounce): 12 mcg
  • Raisin bran cereal, (1 cup): 11 mcg
  • Apple juice (1 cup): 7 mcg
  • Frozen green peas (1/2 cup): 3 mcg
  • Banana (1 medium): 3 mcg

A Word From Verywell

You should only pursue iodine supplementation after discussion with your doctor. This is true whether you have thyroid problems or not. While iodine poisoning is rare, the overconsumption of iodine can be just a problematic as consuming too little.

The only exception is for women who are pregnant, breastfeeding, or pursuing pregnancy in whom a prenatal vitamin is considered essential. Even then, you should work with your OB/GYN to ensure that supplementation is included as part of an appropriate diet.

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