(See also Overview of Minerals Overview of Minerals Minerals are necessary for the normal functioning of the body’s cells. The body needs relatively large quantities of Calcium Chloride Magnesium read more .)
Iodine occurs in seawater. A small amount of iodine from seawater enters the atmosphere and, through rain, enters ground water and soil near the sea.
In many areas, including the United States, table salt is fortified with iodine (in its combination form iodide) to help make sure people consume enough.
Excess consumption of iodine is uncommon. It usually results from taking iodine supplements to treat a prolonged iodine deficiency. Sometimes people who live near the sea consume too much iodine because they eat a lot of seafood and seaweed and drink water that is high in iodine, as is common in northern Japan.
Consuming too much iodine usually does not affect thyroid function, but sometimes it does. It may cause the thyroid gland to become overactive and produce excess thyroid hormones (hyperthyroidism Hyperthyroidism Hyperthyroidism is overactivity of the thyroid gland that leads to high levels of thyroid hormones and speeding up of vital body functions. Graves disease is the most common cause of hyperthyroidism... read more 
), particularly in people who used to consume too little iodine. However, sometimes excess iodine can decrease production of thyroid hormones (causing hypothyroidism Hypothyroidism Hypothyroidism is underactivity of the thyroid gland that leads to inadequate production of thyroid hormones and a slowing of vital body functions. Facial expressions become dull, the voice... read more 
). As a result, the thyroid gland enlarges, forming a goiter. (Goiters can form when the thyroid gland is underactive or overactive.)
If people consume very large amounts of iodine, they may have a brassy taste in their mouth and produce more saliva. Iodine can irritate the digestive tract and cause a rash.
Diagnosis of Iodine Excess
Blood tests
Imaging tests
Doctors suspect hyperthyroidism Hyperthyroidism Hyperthyroidism is overactivity of the thyroid gland that leads to high levels of thyroid hormones and speeding up of vital body functions. Graves disease is the most common cause of hyperthyroidism... read more or hypothyroidism Hypothyroidism Hypothyroidism is underactivity of the thyroid gland that leads to inadequate production of thyroid hormones and a slowing of vital body functions. Facial expressions become dull, the voice... read more due to excess iodine based on symptoms, particularly in people who report taking iodine supplements.
Blood tests to determine levels of thyroid hormones and thyroid-stimulating hormone (TSH) are done. Imaging tests of the thyroid may also be done.
Treatment of Iodine Excess
Dietary changes
Sometimes thyroid hormones
People with excess iodine are advised to use salt that is not fortified with iodine and to reduce their consumption of foods that contain iodine, such as seafood, seaweed, yogurt, and milk, and to avoid taking supplements containing iodine.
If people have hypothyroidism Hypothyroidism Hypothyroidism is underactivity of the thyroid gland that leads to inadequate production of thyroid hormones and a slowing of vital body functions. Facial expressions become dull, the voice... read more due to consuming too much iodine, consuming less iodine often cures the disorder, but some people must take thyroid hormones for the rest of their life.
If people have hyperthyroidism Hyperthyroidism Hyperthyroidism is overactivity of the thyroid gland that leads to high levels of thyroid hormones and speeding up of vital body functions. Graves disease is the most common cause of hyperthyroidism... read more , drugs may be needed to help the thyroid gland function normally.
