Taken from the NIH Fact Sheet for Professionals:
It is difficult to get too much iodine just from food. Most people only take in 200-300 mcg per day.

High intakes of iodine can cause some of the same symptoms as iodine deficiency—including goiter, elevated TSH levels, and hypothyroidism—because excess iodine in susceptible individuals prevents the creation of thyroid. THis y increases TSH stimulation, which can produce goiter. Iodine can also create hyperthyroidism usually when iodine is administered to treat iodine deficiency. Cases of acute iodine poisoning are rare and are usually caused by doses of many grams.

Acute poisoning symptoms include burning of the mouth, throat, and stomach; fever; abdominal pain; nausea; vomiting; diarrhea; weak pulse; and coma.

Responses to excess iodine and the doses required to cause adverse effects vary . Some people, such as those with autoimmune thyroid disease (like Grave's disease or Hashimoto's disease) and those who have been low on iodine at some point in their life, may be more sensitive to the effects of iodine than the general population. They may need to monitor their intake more closely. adverse effects with iodine intakes considered safe for the general population].

* Formula and food should be the only sources of iodine for infants.

Iodine in Table Salt

Iodine-containing compounds are added to table salt. Iodized salt is thus table salt mixed with a very, very small amount of potassium iodide, sodium iodide, or sodium iodate.

 

Iodine - Effect of Low Amounts

Iodized salt is used to help decrease the number of people who did not have enough iodine. Low iodine levels (iodine deficiency) affects about two billion people in the world. It is the leading preventable cause of mental retardation. Iodine was added to salt starting in 1924. Iodine deficiency commonly leads to thyroid gland problems - a 'goiter' which is a swelling of the thyroid gland, usually resulting in a bulbous protrusion on the neck. In the US, this was most common in parts of the country with low iodine in the soil and low intake of food from the ocean. Iodized table salt has significantly reduced disorders of iodine deficiency in countries where it is used.[35]  Not enough iodine results in low levels of thyroid hormones (hypothyroidism), goiter. Low amounts are more common in women and more common during pregnancy.

 

Iodine - Recommended Amount

Iodine is a 'trace mineral' - whcih means it is only needed in smal amounts but it is essential. It is needed for the cells to function nomrally and conver food into energy. The amount of iodine and the specific iodine compound added to salt varies from country to country. In the United States, the recommendation is for 150 micrograms of iodine per day for both men and women.

Table 1: Recommended Dietary Allowances (RDAs) for Iodine [2]

A 1/4 teaspoon of iodized table salt provides 95 micrograms of iodine. (One teaspoon would provide 360 micrograms.) A 6-ounce portion of ocean fish provides 650 micrograms of iodine.

US iodized salt contains 46–77 ppm (parts per million), whereas in the UK the iodine content of iodized salt is recommended to be 10–22 ppm. 

Today, iodized salt is more common in the United States, Australia and New Zealand than in the United Kingdom.

---

If you are concerned about high levels of iodine, talk it over with your physician or a dietitian. You can also use some iodized salt and make up the rest with salt without iodine.