Iodine is an essential mineral, meaning your body needs it to function properly. You can’t produce it on your own and must ingest it through your diet or as a supplement. It’s a trace element, or a relatively small percentage of the body’s tissue. That means your body only needs a small amount of it. Iodine is found in foods, but amounts can be hard to identify. Iodized salt is the main source of this mineral in the United States. Most people need to regularly use salt that is enriched with iodine in order to get enough in their diet.
This article discusses what iodine is used for and how much iodine is recommended. It also covers what happens when you get too little or too much iodine.
What Is Iodine Used For?
Iodine is an important part of thyroid hormones. These hormones help your body regulate weight, internal temperature, and energy levels. They also play a role in skin, hair, and nail growth.2 Iodine may play a role in physical functions besides thyroid hormone production, but the evidence is not completely clear. Your thyroid gland makes the thyroid hormones thyroxine (T4) and triiodothyronine (T3). Both of these 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. From there, iodine receptors (located in the thyroid) bind to it and take it in. The T4 hormone contains four molecules of iodide, while the T3 thyroid hormone contains three molecules of iodide. After the thyroid gland produces T4, it releases it into the bloodstream. T4 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 leads to problems with thyroid hormone production. This results in symptoms of thyroid disease. If you have low iodine levels, symptoms of thyroid dysfunction can develop within a few weeks. They include a variety of conditions:
Hypothyroidism (Low Thyroid Function)
Iodine deficiency prevents your body from making enough thyroid hormones, which causes hypothyroidism.
This can cause a variety of symptoms, including:
- Weight gain
- Diminished energy
- Trouble concentrating
- Feeling cold all the time
- Menstrual irregularities
- Problems with blood sugar4
Dietary iodine deficiency is among the leading preventable causes of cognitive (intellectual) and developmental disabilities in many parts of the world.5 Children who are deficient in iodine may experience the same effects as adults as well as additional symptoms. The effects can be subtle and gradual including slow physical growth, mood problems, trouble concentrating, and learning difficulties.6
With hypothyroidism, your body doesn’t make enough thyroid hormones. It can cause weight gain, decreased energy, trouble concentrating, menstrual irregularities, and more. Children may have these symptoms in addition to slow growth, mood problems, and learning difficulties.
An iodine deficiency results in low thyroid hormone levels. In response, your pituitary gland makes excess thyroid stimulating hormone (TSH) to make up for these low levels.
TSH normally stimulates the thyroid gland to produce and release T4 and T3. However, too much TSH overstimulates the thyroid gland.
The thyroid gland then becomes enlarged but still can’t function adequately without enough iodine. This change is described as goiter.7
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 with 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.
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.
In general, moderate iodine consumption from iodized salt or the food in your diet shouldn’t cause problems. 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.9 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 using supplements may not be able to properly eliminate excess iodine. Symptoms can include stomach upset, vomiting, and diarrhea.9
Iodine Allergies and Sensitivity
Allergies and sensitivities to iodine have been reported. There are three types of iodine reactions:
- 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.10
- Allergies: Allergies to ingested iodine remain a somewhat controversial topic. Seafood allergies have been attributed to iodine in the past. Now medical experts believe that seafood allergies are caused by another component of seafood, not iodine.11
- Contrast (injected) iodine: Contrast material injected for imaging studies often contains iodine. Often, people experience allergic reactions to contrast injection. Whether iodine plays a role in this reaction is unclear. Medical experts currently believe iodine is not the reason behind allergic reactions to contrast dye, but questions remain.12
Allergic reactions have been reported when iodine is ingested in seafood or injected for imaging studies. However, some medical experts question whether these allergies are due to iodine or another component.
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.7
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 suggest inadequate iodine intake.7
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. You can find the specific amount of iodine on the label. Talk with your healthcare provider before taking a supplement.
Iodine levels can be measured in your urine. Normal levels range from 100 to 200 micrograms per liter. Common sources of iodine are salt, supplements, and food such as fish and seaweed.
Radioactive iodine is used as a medical treatment for conditions like thyroid cancer or goiter. It’s often used to destroy overactive thyroid tissue or thyroid cancer.13
This treatment comes as a prescription pill and requires a special low iodine diet several weeks before starting treatment. Radioactive iodine can be harmful to others, so there are precautions to take to protect other people. This includes 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.14
Salt is enriched with iodine and found naturally in some foods. Therefore, iodine supplements aren’t recommended unless you have a deficiency 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. 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 over-the-counter supplement. If so, verify that the dose is exactly as prescribed by your healthcare provider.
Iodine is a mineral your body needs for producing thyroid hormones. These hormones have important roles in regulating body weight, maintaining energy, and growing hair, skin, and nails. Iodine deficiencies can lead to hypothyroidism, where the thyroid doesn’t produce enough thyroid hormones. Common sources of iodine include salt, supplements, and foods like vegetables and seafood. Consult your physician before taking any supplements.
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’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.