A trace mineral is any mineral that the body requires in small amounts to support numerous functions. Iodine is a trace mineral found mostly in the ocean, where it is concentrated by sea life, especially seaweed. The body needs iodine but cannot make it so it must come from the diet. In general, foods from the sea contain the most iodine, followed by animal foods, and then plant foods. There is very little iodine in food, unless it has been added during processing, which is now the case with salt. Early in the twentieth century, iodine deficiency was common in the US and Canada, but the addition of iodine to salt has improved public health. The addition of iodine to salt is required in Canada and though not required in the US, it is widely available. Researchers estimate that iodized salt is used regularly by about half the US population.

Iodine is a component of almost every living plant and animal. No standard measurements of iodine in food exist because iodine concentrations vary across the world.

In your lifetime you will need less than a teaspoon of iodine to ensure good health, however, since it is dangerous to consume that much iodine at once, it is best to eat a little each day. You only need 150 micrograms to meet your daily requirement. Iodine deficiencies are rare in the US and are found in people who live in a part of the world with low levels of iodine in the soil or sea and in people who eat high amounts of refined foods that lose their iodine content during refinement.

The thyroid gland needs iodine to make hormones. If the thyroid doesn’t have enough iodine to do its job, feedback systems in the body cause the thyroid to work harder. This can cause an enlarged thyroid gland also known as a goiter, which becomes evident as a swollen neck. Iodine deficiency and the resulting low levels of thyroid hormone can cause women to stop ovulating, leading to infertility. It can also lead to an autoimmune disease of the thyroid and may increase the risk of getting thyroid cancer. Some researchers think that iodine deficiency might also increase the risk of other cancers such as prostate, breast, endometrial, and ovarian cancer.

Iodine deficiency during pregnancy is serious for both the mother and the baby. It can lead to high blood pressure during pregnancy for the mother, and mental retardation for the baby. It is a common world health problem and across the globe- iodine deficiency is thought to be the most common preventable cause of mental retardation. Iodine plays an important role in development of the central nervous system. In extreme cases, iodine deficiency can lead to cretinism, a disorder that involves severely stunted physical and mental growth. There are no tests to confirm if you have enough iodine in your body. Since even mild deficiency during pregnancy can have effects on delivery and the developing baby, all pregnant and breastfeeding women should take a multivitamin containing the RDA of 150 μg iodine per day.

Individuals who add table salt to their food regularly should use iodized salt. One teaspoon of iodized salt contains approximately 400 μg iodine though most people don’t eat that much per day. Taking too much iodine can also cause problems. This is especially true in individuals that already have thyroid problems, such as nodules, hyperthyroidism and autoimmune thyroid disease. Administration of large amounts of iodine through medications, radiology procedures and dietary excess can cause or worsen hyperthyroidism and hypothyroidism.

Individuals who move from an iodine-deficient region as found in parts of Europe, to a region with adequate iodine intake like the US may also develop thyroid problems since their thyroids have become very good at taking up and using small amounts of iodine. These patients may develop iodine-induced hyperthyroidism.