What Is Iodine?

Iodine is an essential mineral, meaning your body needs it to function properly. You can't produce it independently and must ingest it through your diet or as a supplement.

Iodine is important for thyroid function. The thyroid is a butterfly-shaped organ in your neck that produces hormones that regulate bodily activities, like metabolism (the conversion of food to energy).

You can find iodine in foods, but amounts can be hard to identify. Iodized salt is the primary source of this mineral in the United States. Most people should regularly use salt enriched with iodine to get enough in their diet.

This article discusses the benefits of iodine and how much iodine you need. It also covers what happens when you get too little or too much iodine.

Uses of Iodine

Iodine is an essential part of the thyroid hormones thyroxine (T4) and triiodothyronine (T3) made by your thyroid gland. Both of these hormones contain iodide (a form of iodine). Thyroid hormones have the following functions in the body:

• Help cells make protein
• Regulate activity of enzymes (proteins that create chemical reactions in the body)
• Determine metabolism

For the most part, people take iodine to prevent or treat iodine deficiency, which can cause problems with fetal development, cognitive function, and thyroid function. In addition, some people use iodine for fibrocystic breasts and to prevent thyroid cancer when exposed to radiation. Some of these uses are better supported by research than others.

Fetal Development

Since 50% more iodine is required during pregnancy to meet fetal developmental needs, some research has examined how iodine deficiency impacts fetal development.

For example, in a 2013 study published in Lancet, researchers evaluated the effect of insufficient iodine in pregnancy on cognitive outcomes in children. Researchers measured urinary iodine concentration in 1,040 pregnant participants during the first trimester. Later, they also measured the children's intelligence quotient (IQ) at age 8.

Compared to those with adequate iodine, those with mild-to-moderate iodine deficiency were more likely to have the lowest scores for verbal IQ, reading accuracy, and reading comprehension.

In addition, a 2019 study published in Nutrients evaluated educational outcomes in adolescents whose gestational parents had mild iodine deficiency in pregnancy.

First, researchers assessed the iodine concentration of 266 pregnant people attending antenatal clinics at the Royal Hobart Hospital in Australia from 1999 to 2000. Then, researchers compared their children's standardized test scores in literacy and math when they were ages 8–9, 10–11, 12–13, and 14–15 years.

The study found that even mild iodine deficiency in pregnancy had long-term cognitive effects. However, these effects did not resolve with sufficient iodine intake during childhood. For example, children whose parents had iodine deficiency in pregnancy had reduced scores in reading, spelling, and grammar, independent of other factors known to impact learning.

Fibrocystic Breasts

Fibrocystic breasts are a benign condition where breast tissue is lumpy. Since breast tissue has a high concentration of iodine, some research has evaluated whether the mineral could be helpful in fibrocystic breasts.

For example, in a 2018 study published in the Journal of Women's Health, researchers evaluated whether a nutritional supplement including iodine could decrease cyclical breast pain and nodules. The randomized, multi-center, controlled, double-blind trial included 188 participants.

Researchers randomized participants to receive either a nutritional formula containing 1 gram (g) gamma-linolenic acid (GLA), 750 micrograms (mcg) iodine, and 70 mcg selenium, or a placebo daily for three menstrual cycles. While breast pain decreased in both groups, nodules decreased in the supplement group but not in the control group.

Radiation-Induced Thyroid Cancer

Nuclear accidents can release radioactive iodine (Iodine-131) into the environment, increasing the risk of thyroid cancer in those exposed. Therefore, some research has evaluated whether iodine supplementation could reduce cancer risk in high-risk populations following some historic nuclear disasters.

For example, in 1993, the American Journal of Medicine published a study examining the benefits and risks of iodide supplements in Poland following the 1986 Chernobyl nuclear power plant meltdown. That study found that where potassium iodide was widely used, thyroid cancer rates did not increase substantially in the following years. On the other hand, in Belarus and Ukraine, where people did not use iodine supplements, thyroid cancer increased significantly among children and adolescents.

Other

Other uses mainly include managing thyroid conditions caused by an iodine deficiency. Those uses are explored more below.

Iodine Deficiency

If your iodine intake falls below 10–20 mcg/day, you may become deficient. Iodine deficiency leads to problems with thyroid hormone production, which can result in thyroid disease, including goiter (enlarged thyroid) and hypothyroidism (underactive thyroid).

In addition, iodine deficiency can lead to cognitive disabilities in children whose gestational parents did not have adequate intake during pregnancy.

What Causes an Iodine Deficiency?

Since the body does not make iodine on its own, you need to obtain enough of it in your diet. If you do not get enough iodine through diet or supplements, you may become deficient.

Since the introduction of iodized salt, iodine deficiency has been rare in the U.S. However, some groups are at increased risk for a deficiency, including:

• People who don't use iodized salt
• Pregnant people
• Vegans
• Those with marginal iodine status who eat goitrogens (foods that interfere with the uptake of iodine in the thyroid)

Some goitrogens include broccoli, cabbage, cauliflower, kale, and strawberries. If you have normal thyroid function and iodine intake, you don't need to worry about these foods causing an iodine deficiency. 

How Do I Know If I Have an Iodine Deficiency?

Goiter is often the first clinical sign of iodine deficiency. A goiter is an enlarged thyroid that is sometimes visible or palpable through the neck. This enlargement happens because the thyroid grows so it can try to absorb as much iodine as possible.

Goiter symptoms include:

• Neck lump
• Throat tightness
• Coughing
• Hoarseness
• Trouble breathing or swallowing

In addition, if you have iodine deficiency, you may develop hypothyroidism. This happens because the thyroid has too little iodine to make thyroid hormone.

Hypothyroidism can cause a variety of symptoms, including:

• Weight gain
• Diminished energy
• Sleepiness
• Dry skin
• Trouble concentrating
• Depression
• Constipation
• Feeling cold all the time

Children with hypothyroidism may experience the same effects as adults and additional symptoms, including slow physical growth, mood problems, trouble concentrating, and learning difficulties.

Newborn screening tests can detect iodine deficiency in infants. Deficiency may cause babies to develop congenital hypothyroidism. Symptoms may include trouble eating, being excessively sleepy, or having constipation. Sometimes, it may not cause any symptoms at all.

What Are the Side Effects of Iodine?

Your provider may recommend you take iodine during pregnancy or for deficiency. However, consuming a supplement like iodine may have potential side effects. These side effects may be common or severe.

Common Side Effects

In general, moderate iodine consumption from iodized salt or the food in your diet shouldn't cause problems. That is because the body eliminates extra iodine through the urine.

Allergies and sensitivities to iodine have been reported. However, more recent research suggests that iodine allergies may actually be due to another substance and not iodine. Usually, this occurs with exposure to iodine contrast material for medical testing, not from iodine supplements.

For example, a 2021 review in the American Journal of Health System Pharmacy looked at common misperceptions of iodine allergy. Researchers found that among 81 articles, iodine was not seen as the allergen responsible for allergic reactions to iodinated contrast media, amiodarone (a drug that regulates heart rate), povidone-iodine (antiseptic skin disinfectant used before surgery), and other iodine-containing compounds.

Mild allergic reactions to iodine contrast materials include:

• Headache
• Nausea
• Hives
• Rash
• Sweating

Severe Side Effects

Although rare, allergic reactions can also be severe. Anaphylaxis is a life-threatening emergency that can occur without warning due to exposure to an allergen. Symptoms include:

• Hives
• Throat swelling
• Wheezing
• Unconsciousness
• Hoarseness
• Trouble swallowing
• Vomiting
• Diarrhea
• Face flushing

If you experience any of the above symptoms, it is critical to seek emergency medical care immediately.

Precautions

Iodine supplements may interact with some medications, including:

• Anti-thyroid drugs used to treat hyperthyroidism (overactive thyroid)
• Angiotensin-converting enzyme (ACE) inhibitors used to treat high blood pressure and heart disease
• Potassium-sparing diuretics, such as Aldactone (spironolactone) and Midamor (amiloride)

If you take any medications, talk to a healthcare provider or pharmacist about the safety of any supplements you consider taking.

Dosage: How Much Iodine Should I Take?

Always speak with a healthcare provider before taking a supplement to ensure that the supplement and dosage are appropriate for your individual needs. 

Since your body produces thyroid hormones on an ongoing basis, all children and adults need to consume iodine regularly. In addition, pregnant people need higher amounts to support the developing fetus.

The United States Institute of Medicine recommends the amount of iodine a person should ingest daily.

You can not measure iodine levels in the blood, but you can measure it in the urine. Normal urinary iodine concentrations range between 100 and 200 micrograms per liter. Values lower than 20 micrograms per liter suggest inadequate iodine intake.

Medical Use

Radioactive iodine is a medical treatment for conditions like thyroid cancer or goiter. It works by destroying overactive thyroid tissue or thyroid cancer cells.

This treatment comes as a prescription pill and requires a special low iodine diet one to two weeks before starting treatment.

Radioactive iodine can be harmful to others, so healthcare providers recommend precautions to protect other people. Precautions include maintaining distance from other people while your body gives off radiation.

What Happens If I Take Too Much Iodine?

You can consume more iodine than your body can handle by using supplements that contain high doses of iodine. Chronic iodine overdose is associated with goiter, hyperthyroidism (overactive thyroid), thyroiditis (thyroid inflammation), and thyroid cancer.

Toxicity is rare but can occur from consuming heavy doses (usually many grams) of iodine supplements. Signs of iodine poisoning include:

• Mouth, throat, or stomach burning
• Fever
• Abdominal pain
• Nausea
• Vomiting
• Diarrhea
• Weak pulse
• Coma

To avoid toxicity, be aware of the appropriate dosage (above) and stay below the safe upper limit established by the Institute of Medicine.

If you consume more than these amounts or more than what is recommended by your healthcare provider, you may want to go to the emergency room. 

How to Store Iodine

Store iodine in a cool, dry place. Keep it away from direct sunlight. Discard after one year or as indicated on the packaging.

Sources of Iodine and What To Look For

Iodine is found in food sources and is also available as a supplement. Most people can meet their iodine needs through food sources.

Food Sources of Iodine

The most common source of iodine is iodized salt, which contains 76 mcg (51% of the daily recommended intake for adults) in a quarter teaspoon. However, this concentration may differ depending on the manufacturer. For precise amounts, check the label’s nutritional information.

In addition, plenty of foods contain iodine. Fish and seaweed are the foods richest in iodine. For example, one 3-ounce serving of cod contains about 158 mcg of iodine, and one serving of seaweed contains about 116 mcg of iodine. Other iodine-rich foods include:

• Bread made with iodate dough
• Oysters
• Yogurt
• Milk
• Enriched pasta boiled in iodized salt
• Eggs
  

Supplements

Vitamins and supplements vary in their iodine content. You can find the specific amount of iodine on the label. Talk with your healthcare provider before taking a supplement.

Iodine supplements most often come as potassium iodide or sodium iodide. Some iodine supplements are also sourced from kelp (seaweed). They are available in drops, capsules, and tablets. If you are vegan or have food allergies, read labels carefully to ensure there are no animal products or allergens.

Iodine is quickly absorbed in the stomach and small intestine. Next, it travels through the bloodstream. From there, iodine receptors located in the thyroid bind to it and take it in.

Do not use iodine supplements unless you are diagnosed with iodine deficiency. If you need iodine supplements, your healthcare provider will give you a prescription. You might be able to use an OTC supplement. If so, verify that the dose is exactly as prescribed by your healthcare provider.

Summary

Iodine is a mineral your body needs for producing thyroid hormones. These hormones have essential roles in regulating body weight and maintaining energy.

Iodine deficiency can lead to hypothyroidism, where the thyroid doesn't produce enough hormones. It can also cause an enlarged thyroid, called a goiter.

Common sources of iodine include salt, supplements, and foods like vegetables and seafood. Consult a healthcare provider before taking any supplements.

A Word From Verywell

Iodine deficiency is rare in countries where iodized salt is regularly used. However, if you have a thyroid problem, a healthcare provider may instruct you to maintain a low iodine diet or supplement your diet with iodine.

If you've had an iodine deficiency in the past, check with your doctor about regular monitoring of your thyroid hormone levels. Regular check-ups are the best way to know whether you are getting enough iodine.