What Is Iodine?

Iodine is an essential mineral, which means that your body needs it to function properly and you cannot produce it on your own—you must ingest it through your diet or as a supplement. It is present in foods, but amounts can be hard to identify. Most people need to regularly use salt that is enriched with iodine in order to get an ample dietary dose.

Iodized salt is the main source of this mineral in the United States. Additionally, iodine is a trace element, which means that it comprises a relatively small percentage of the body’s tissue.


What is Iodine and How Does the Supplement Work?

Iodine deficiency results in low thyroid hormone levels, which can result in hypothyroidism. This is an uncommon problem, but it can occur in infants and very young children. Dietary iodine deficiency is among the leading preventable causes of cognitive and developmental disabilities in many parts of the world. Iodine may also play a role in physical functions besides thyroid hormone production, but the evidence is not completely clear.

Common sources of iodine
Verywell / JR Bee

What Is Iodine Used For?

Iodine is a vital component of thyroid hormones, which is the mineral’s most important and well-understood function. Your thyroid gland makes the thyroid hormones thyroxine (T4) and triiodothyronine (T3), both of which contain iodide (a form of iodine).

Iodine is consumed by mouth and is quickly absorbed in the stomach and small intestine. It travels through the bloodstream and from here, iodine receptors (located in the thyroid) bind to it and take it in.

T4, which contains four molecules of iodide, is an inactive precursor of the active T3 thyroid hormone, which contains three molecules of iodide. This means that after the thyroid gland produces T4 and releases it into the bloodstream, it is then converted to T3, which interacts with most cells of the body.

The active T3 thyroid hormone functions in virtually every cell and organ in the body by regulating metabolism, energy use, growth, and repair.

Iodine Deficiency

The most noticeable consequences of iodine deficiency involve defects in thyroid hormone production, which results in symptoms of thyroid disease. If you have low iodine levels, the symptoms of thyroid dysfunction can develop within a few weeks and include a variety of conditions:

Hypothyroidism (Low Thyroid Function)

Inadequate iodine prevents your body from making enough thyroid hormones. This can cause a variety of symptoms, including weight gain, diminished energy, sleepiness, trouble concentrating, depression, constipation, feeling cold all the time, menstrual irregularities, and problems with blood sugar.

Childhood Hypothyroidism

Children who are deficient in iodine may experience the same effects as adults, as well as experience additional symptoms. The effects can be subtle and gradual including slow physical growth, mood problems, trouble concentrating, and learning difficulties.


When an iodine deficiency results in low thyroid hormone levels, your pituitary gland makes excess thyroid stimulating hormone (TSH) to compensate for the low thyroid hormone levels. TSH normally stimulates the thyroid gland to produce and release T4 and T3. Excess TSH overstimulates the thyroid gland. In response to this, the thyroid gland becomes enlarged, yet still cannot function adequately in the absence of sufficient iodine. This change is described as goiter.

Congenital Hypothyroidism

Iodine deficiency in infants is detected by newborn screening tests. The condition may cause babies to experience trouble eating, weak muscle tone, or heart problems—sometimes, it may not cause any symptoms at all. While there are other causes, newborn babies born to mothers who had low iodine intake during pregnancy can develop congenital hypothyroidism. The condition can improve if infants get enough iodine in their diet after they are born. If they don't, they are at risk for developing learning deficits and limits in physical growth as a result of inadequate thyroid function.

It has been suggested that iodine deficiency may also be associated with breast disease, stomach problems, and bone problems, but these concerns have not been verified.


In some situations, your iodine might not function the way it should if goitrogens interfere with iodine absorption in the thyroid gland.

Goitrogens are foods and other substances that compete with iodine uptake in your thyroid gland, ultimately preventing proper production of thyroid hormones.

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. 

Side Effects

In general, moderate iodine consumption through the intake of iodized salt or through the food in your diet should not be problematic because extra iodine is easily eliminated through the urine.

However, you can consume more iodine than your body can handle by using supplements that contain high doses of iodine. Chronic iodine overdose has been associated with goiter, hyperthyroidism, thyroiditis, and thyroid cancer.

In rare instances, iodine toxicity can occur as a result of consuming heavy doses of iodine supplements.

Children who eat a whole bottle of vitamin pills or adults with kidney failure who use supplements may not be able to properly eliminate excess iodine. Symptoms can include stomach upset, vomiting, and diarrhea.

Iodine Allergies and Sensitivity

Allergies and sensitivities to iodine have been reported. There are three types of iodine reactions: skin sensitivity, an allergy to ingested iodine, and an allergy to injected iodine.

  • Skin Sensitivity: Topical iodine (used directly on the skin) can cause skin redness and pain. This reaction is generally self-limited and typically resolves on its own within a few hours.
  • Allergies: Allergies to ingested iodine remain a somewhat controversial topic. Seafood allergies have been attributed to iodine in the past, but now medical experts believe that seafood allergies are caused by another component of seafood, not iodine.
  • Contrast Iodine: Contrast material injected for imaging studies often contain iodine. Often, people experience allergic reactions to contrast injection. Whether iodine plays a role in this reaction is unclear. As with the concerns about ingested iodine in seafood, medical experts currently believe that iodine is not the reason behind allergic reactions to contrast dye, but questions remain.

Dosage and Preparation 

Iodine is added to table salt, which is labeled as "iodized salt." Since thyroid hormones are produced on an ongoing basis, all children and adults need to regularly consume iodine. Pregnant women need higher amounts to support the developing baby. The United States Institute of Medicine produced a recommendation for the amount of iodine a person should ingest on a daily basis.

Recommended Iodine Intake

  • 90-130 micrograms per day for children (depending on age)
  • 150 micrograms per day for adults (and teens 14-18)
  • 220 micrograms per day for pregnant women

Measuring Iodine Levels

Iodine levels are not measured in the blood, but they can be measured in the urine. Urine measures of iodine are considered a reflection of iodine intake.

Normal urinary iodine concentrations range between 100 and 200 micrograms per liter. Values lower than 20 micrograms per liter are suggestive of inadequate iodine intake.

Common sources of iodine include:

  • Salt: Iodized salt contains an average of 45 micrograms of iodine per gram. This concentration may differ depending on the manufacturer. For precise amounts, check the label’s nutritional information.
  • Food: Iodine is a component of seafood, milk, vegetables, and fruit. Fish and seaweed are the foods richest in iodine— one serving of fish contains about 90 micrograms of iodine and one serving of seaweed contains about 200 micrograms of iodine.
  • Supplements: Vitamins and supplements vary in their iodine content, and you can find the specific amount of iodine on the label. If you use any type of vitamin or supplement, be sure to let your healthcare provider know If you have a medical condition–do not use supplements before consulting with your healthcare provider.

Medical Use

As a medical treatment, radioactive iodine is used for several purposes, including for treatment of thyroid cancer or goiter. Radioactive iodine is often used to destroy overactive thyroid tissue or thyroid cancer.

This treatment comes as a prescription pill and requires preparation with a special low iodine diet several weeks before starting treatment. Radioactive iodine can be harmful to others, and there are precautions that you would need to take to protect other people, including covering your neck for the duration of your treatment.

Over-the-counter and prescription forms of iodine solution are often used to prevent infections. The mineral is often added to topical antiseptics and is believed to destroy infectious microorganisms with minimal risk of side effects.

Iodine is also used for pre-surgical care. It is a component of povidone-iodine, which is one of the preparations used for surgical procedures to prevent infections.

In rare instances, a nuclear emergency associated with a radioactive iodine leak can pose serious health threats to the public. In these instances, potassium iodide can be used to prevent thyroid gland damage.

What to Look For

Because salt is enriched with iodine and is naturally found in some foods, it is not recommended to use iodine supplements unless you have a deficiency that is diagnosed by your healthcare provider. In fact, with a thyroid disorder, a low iodine diet is often recommended. If you have to follow a very low salt diet due to other health issues, you may need iodine supplementation.

If you need iodine supplements, your healthcare provider will give you a prescription. You might be able to use an over-the-counter supplement, and if so, be sure to verify that the dose is exactly as prescribed by your healthcare provider.

Other Questions About Iodine and Health

Can iodine deficiency cause low energy levels?

Iodine deficiency can affect your thyroid hormone levels, causing low energy. However, iodine deficiency does not affect energy levels independently of thyroid hormones. You can have your thyroid levels checked if you have low energy or other symptoms of thyroid disease.

Can eating salty foods cause iodine toxicity?

If you have a tendency to eat salty foods, your body will eliminate the excess iodine. Food alone should not cause toxicity—consuming excess supplements, however, is not safe.

Do not use iodine supplements unless you are diagnosed with iodine deficiency.

A Word From Verywell

Iodine deficiency is rare in countries where iodized salt is regularly used. If you have a thyroid problem, you may have been instructed to maintain a low iodine diet or to supplement your diet with iodine. If you have had an iodine deficiency in the past, regular monitoring of your thyroid hormone levels is considered the best way to know whether you are getting enough iodine.

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14 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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