Iodine is an essential constituent of your thyroid hormones, which help regulate metabolism (the rate at which your body uses energy). Iodine is a key player in many biochemical reactions that affect heart rate, respiratory rate and a wide variety of other physiological activities.
The iodine content in foods varies widely due to soil content, irrigation and fertilizer. It is usually low in areas that are eroded or are distant from oceans, the source of most of the world’s iodine. Seafood and seaweed are rich natural sources. Processed foods may contain higher levels due to the addition of iodized salt or other additives containing iodine (e.g., calcium iodate). In the United States, iodized salt is widely available. However, salt is not required to be iodized. One-fourth of a teaspoon of iodized table salt contains about 100 micrograms of iodine.
Due to the widespread use of iodized salt, deficiency is rare in the United States. However, iodine deficiency affects millions of people worldwide and is identified as the most common cause of preventable brain damage in the world. Major international efforts are currently under way to reverse and prevent this problem. Iodine deficiency disease (IDD) results in a range of symptoms from mild to severe including goiter (an enlarged thyroid gland and usually the earliest sign), mental retardation, hypothyroidism (too little thyroid hormone), and varying degrees of growth and development abnormalities.
Individuals can tolerate a wide range of iodine intakes because the thyroid gland regulates the body’s level of this mineral. Acute intakes—those ingested over a short time period—can cause burning of the mouth, throat and stomach; fever; gastrointestinal illness, such as nausea, vomiting and diarrhea; a weak pulse; and coma. In iodine-sufficient populations, chronic intakes at levels above the tolerable upper intake level (UL) have the following adverse effects: goiter (an enlarged thyroid gland), hypothyroidism (too little thyroid hormone), hyperthyroidism (too much thyroid hormone) and thyroiditis (inflammation of the thyroid gland).
The following table lists the recommended intake for healthy people based on current scientific information.