Everything You Need To Know about Iodine

Medically reviewed by Jamie Johnson, RDNMedically reviewed by Jamie Johnson, RDN

Iodine is a nonmetal trace element the body needs to make thyroid hormones. These hormones control many body functions, such as making proteins, enzyme activity, and metabolism. They also affect fertility and the hormones involved in the body's stress response. Thyroid hormones are vital for the proper growth and development of the bones and brain in fetuses and infants.

You can get iodine through several food sources as well as supplements. Certain groups, including people who are pregnant, may be at higher risk for an iodine deficiency.

Potential Benefits of Iodine

Research on iodine's benefits primarily focuses on its effect on thyroid health, though it may also have potential benefits for conditions like fibrocystic breast changes.

Supports Thyroid Health

It's important to have an adequate intake of iodine for thyroid health, as it's an essential component of the thyroid hormones thyroxine (T4) and triiodothyronine (T3). These hormones play a vital role in many bodily functions.

Thyroid hormones help control metabolism and important body functions, such as heart rate, how much blood the heart pumps, and the delivery of oxygen to tissues. They're also vital for reproductive health.

T3 plays a key role in bone development before and after birth. In adults, T3 helps with bone remodeling, the process of breaking down old bone and building new bone. T3 also strengthens the nervous system, making you more awake, alert, and responsive. Additionally, it improves reflexes and aids digestion.

Can Protect Against Thyroid Deficiency in Pregnancy

The recommended iodine intake increases during pregnancy as iodine plays a crucial role in the development of the fetus's skeletal and nervous systems. Many pregnant people may have insufficient iodine intake, even without showing signs or symptoms of deficiency.

However, iodine deficiency can lead to goiter (enlarged thyroid gland), miscarriage, and negative effects on the baby's development. A research review found that pregnant people who supplemented with 200 micrograms (mcg) of iodine daily starting in the first trimester could improve or maintain their iodine levels during pregnancy. This can help prevent health problems caused by iodine deficiency.

May Lower the Risk of Thyroid Nodules

Thyroid nodules refer to the abnormal growth of thyroid cells, forming lumps within the thyroid gland. They are extremely common, and most cases are benign, though a small proportion may be cancerous. The causes of most thyroid nodules are not well known, but iodine deficiency is a known cause. Thyroid nodules occur more often in iodine-deficient populations.

Might Ease Pain Associated With Fibrocystic Breast Changes

Fibrocystic breast disease causes lumpy, painful breasts in females of reproductive age and during menopause, especially with estrogen use. Iodine supplements might help, according to older studies, but more research is needed to validate these findings and understand how this works.

One study involving a small group of people found that those with fibrocystic breast changes who used a nutritional formula containing gamma-linolenic acid, iodine, and selenium had fewer lumps in their breasts. This is linked to experiencing less cyclical breast pain.

Other Uses and Benefits of Iodine

The benefits of iodine extend beyond its use as an oral supplement. Iodine may be effective as a topical agent and rinsing solution. Topical iodine has been found to aid in healing diabetic foot wounds and venous leg ulcers. Also, research has shown that rinsing the mouth with a solution containing iodine may benefit some oral conditions like oral mucositis and periodontitis.

How Much Do You Need?

The recommended dietary allowances (RDAs) for iodine vary based on age and whether you’re pregnant or lactating.

Here are the RDAs for iodine based on age group:

• Birth-6 months: 110 micrograms (mcg)

• 7-12 months: 130 mcg

• 1-8 years: 90 mcg

• 9-13 years: 120 mcg

• 14-18 years: 150 mcg

• 19 years and over: 150 mcg

For pregnant or lactating individuals, the RDAs for iodine are higher. The RDA for iodine is 220 mcg for pregnant people 14 years and older and 290 mcg for lactating people 14 years and older.

Good Sources of Iodine

Generally, seaweed, fish, dairy foods, and commercially prepared bread made with iodate dough conditioner are rich in iodine. Here are some examples of excellent iodine sources, each providing at least 20% of the daily value (DV) for this nutrient:

• White bread made with iodate dough conditioner: 296 mcg per 2 slices, or 197% of the DV

• Whole wheat bread made with iodate dough conditioner: 273 mcg per 2 slices, or 182% of the DV

• Cod: 146 mcg per 3-ounce (oz) baked serving, or 97% of the DV

• Dried nori seaweed: 116 mcg per 2-tablespoon (tbsp) serving, or 77% of the DV

• Oysters: 93 mcg per 3-oz cooked serving, or 62% of the DV

• Nonfat plain Greek yogurt: 87 mcg per 0.75 cup, or 58% of the DV

• Nonfat cow's milk: 84 mcg per cup, or 56% of the DV

• Fish sticks: 57 mcg per 3 oz cooked, or 38% of the DV

• Eggs: 31 mcg per large egg, or 21% of the DV

Iodized Salt

The United States and some other countries add iodine to table salt to address iodine deficiency. Iodized salt in the U.S. contains 45 mcg of iodine per gram (g) of salt. However, specialty salts like sea salt, kosher salt, and Himalayan salt are typically not iodized.

While most salt intake in the U.S. comes from processed foods, food manufacturers usually use non-iodized salt in their products. If iodized salt is used, it will be listed in the ingredients.

Supplements

In dietary supplements, iodine is usually found as potassium iodide or sodium iodide. There are also supplements made from kelp, a type of seaweed with iodine.

Many multivitamins and mineral supplements contain iodine, usually 150 mcg. Some prenatal vitamins also contain iodine. There are supplements that contain only iodine, and some of these have high doses, sometimes above the upper limit.

It's best to consult a healthcare provider before taking iodine or any type of dietary supplement.

Potential Risks and Side Effects

Large iodine intake or long-term doses can lead to goiter, which is an enlarged thyroid gland. Excess intake can also cause problems like sore teeth and gums, mouth and throat burning, increased saliva, runny nose, eye irritation and swelling, lung issues, swollen glands, breathing problems, skin rashes, stomach upset, diarrhea, loss of appetite, and depression.

The Tolerable Upper Intake Level (UL) is the highest amount of a nutrient you can regularly consume from all sources without risking health problems. The ULs for iodine, including intake from all sources (food, drinks, and supplements), are listed below. These limits don't apply to people using iodine for medical reasons under a healthcare provider's care.

• Birth-12 months: Not possible to establish

• 1-3 years: 200 mcg

• 4-8 years: 300 mcg

• 9-13 years: 600 mcg

• 14-18 years: 900 mcg

• 19+ years; 1,100 mcg

• Pregnancy and lactation 14-18 years: 900 mcg

• Pregnancy and lactation 19+ years: 1,100 mcg

Iodine Deficiency

Most people in the U.S. get enough iodine, but some pregnant people might not. Iodine deficiency happens when there isn't enough iodine to make thyroid hormones.

This can lead to hypothyroidism (underactive thyroid) and goiter. Iodine deficiency can cause growth and development problems and is the leading preventable cause of intellectual disability worldwide.

In pregnant people, severe iodine deficiency can harm the fetus, causing stunted growth, intellectual disability, and delayed sexual development. Even mild iodine deficiency can lower IQ in children and reduce adults' ability to work and think clearly.

Groups at risk for iodine deficiency include:

• People who don't use iodized salt

• Pregnant people

• Individuals who eat few or no dairy products, eggs, and seafood

• People living in areas with iodine-deficient soils

• Individuals with low iodine levels who eat foods containing goitrogens. Goitrogens, found in soy, cassava, and cruciferous vegetables, interfere with iodine uptake in the thyroid.
  

Interactions

Iodine supplements have the potential to interact with the below medications. Always consult your healthcare provider before taking an iodine supplement or any other supplement, especially if you have a medical condition or are taking medications.

• Antithyroid medications: Taking high doses of iodine supplements with antithyroid medications such as Tapazole (methimazole) can add to their effects and may lead to hypothyroidism.

• Angiotensin-converting enzyme (ACE) inhibitors: These medications, such as Lotensin (benazepril), Prinivil (lisinopril), and Monopril (fosinopril), are used to treat hypertension (high blood pressure). Taking them with potassium iodide can increase the risk of hyperkalemia (elevated blood potassium levels).

• Potassium-sparing diuretics: Potassium-sparing diuretics like Aldactone (spironolactone) and Midamor (amiloride) increase urination without losing potassium. Taking these medications with potassium iodide can raise the risk of hyperkalemia.

• Coradone (amiodarone): Amiodarone is used to treat irregular heartbeats. Taking it with iodine supplements may cause excessively high iodine levels.

• Lithium: Lithium is used to treat mood disorders. Taking it with iodine can increase the risk of hypothyroidism.
  

A Quick Review

Iodine is a nonmetal trace element essential for producing thyroid hormones. These hormones play a key role in metabolism, growth, development, and hormone interactions. Iodine is especially important during pregnancy and breastfeeding to support fetus development.

You can find iodine in foods like seaweed, fish, dairy, and eggs, as well as iodized salt and supplements. If you're concerned about your iodine intake or think you might need a supplement, talk to your healthcare provider first.

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