Iodine is an element found in small amounts in your body. Your body needs iodine to make thyroid hormones, which regulate your growth, metabolism, and other important functions.

Few foods naturally contain iodine, so manufacturers started adding it to table salt to prevent iodine deficiency. Other food sources of iodine include shrimp, boiled eggs, cooked navy beans, and unpeeled potatoes.

Most adults should try to get about 150 micrograms (mcg) of iodine per day. The Linus Pauling Institute provides a list of tolerable upper intake levels (the maximum amount of iodine someone can consume without any negative side effects) for different age groups:

  • children ages 1 to 3: 200 mcg per day
  • children ages 4 to 8: 300 mcg per day
  • children ages 9 to 13: 600 mcg per day
  • adolescents ages 14 to 18: 900 mcg per day
  • adults ages 19 and older: 1,100 mcg per day

Consuming more than the tolerable upper intake level for your age group can lead to iodine poisoning.

If you or someone you’re with may have iodine poisoning, seek emergency medical treatment. Have the following information handy if possible when you call 911 or get to the hospital:

  • how much iodine was taken
  • the person’s height and weight
  • any underlying conditions they may have, especially anything involving the thyroid

The symptoms of iodine poisoning range from fairly mild to severe, depending on how much iodine is in your system.

More mild symptoms of iodine poisoning include:

  • diarrhea
  • burning sensation in your mouth
  • nausea
  • vomiting

Severe symptoms of iodine poisoning include:

  • swelling of your airways
  • turning blue (cyanosis)
  • weak pulse
  • coma

Consuming too much iodine can also lead to a condition called iodine-induced hyperthyroidism. This usually happens when people take iodine supplements to improve their thyroid function.

Symptoms of hyperthyroidism include:

  • fast heart rate
  • muscle weakness
  • warm skin
  • unexplained weight loss

Hyperthyroidism is particularly dangerous if you have an underlying heart condition, since it affects your heart rate.

Several types of seafood, including shrimp, cod, and tuna, contain iodine. Seaweed also contains very high levels of iodine. In cultures that eat a lot of seaweed, people sometimes consume thousands of mcg of iodine per day.

For example, a 2001 review estimated that people in Japan consume between 1,000 to 3,000 mcg of iodine a day, mostly from seaweed. This causes iodine-induced hyperthyroidism and goiters to be more common in Japan. However, this same review also suggests that this higher intake of iodine may play a role in Japan’s low cancer rates and long life expectancy.

Iodine poisoning usually results from taking too many iodine supplements. It’s very hard to get iodine poisoning from food alone. Remember, adults can tolerate up to 1,100 mcg a day.

Taking a one-time dose of too much iodine usually won’t cause iodine poisoning. However, your risk increases if you consistently take in too much iodine. The extra iodine confuses your thyroid, causing it to produce extra thyroid hormone. This leads to a phenomenon called the Wolff-Chaikoff effect, which is a decrease in thyroid hormone production that usually lasts for about a week.

Certain medications can also increase the amount iodine in your system. Amiodarone, a medication used to regulate heart rate and rhythm, contains 75 milligrams (mg) of iodine in each 200-mg tablet. This is hundreds of times higher than the standard recommended daily intake of 150 mcg. Potassium iodide supplements and contrast dye, which is used for CT scans, also contain iodine.

Even if you don’t take iodine supplements, certain things can make you more sensitive to iodine, which increases your risk of developing iodine poisoning. These including thyroid conditions, such as:

Having a thyroidectomy, which removes all or part of your thyroid gland, also makes you more sensitive to iodine, increasing your risk of iodine poisoning.

Iodine poisoning usually requires a trip to the hospital. Depending on how severe your symptoms are, your doctor might give you medication to make you vomit. They may also give you activated charcoal, which can help to prevent your body from absorbing iodine.

For more severe symptoms, such as breathing problems, you may need to be hooked up to a ventilator until your iodine levels decrease.

Iodine poisoning tends to affect people who take iodine supplements or have a thyroid condition. Mild cases of iodine poisoning usually don’t cause any lasting problems, especially if you seek medical treatment as soon as possible. However, more severe cases can have lasting effects, such as narrowing of your windpipe. For the best outcome, it’s important to get emergency treatment at the first sign of iodine poisoning.