Iodine: The Thyroid Connection

Though the element iodine is poisonous in its gaseous state, the iodine ion (iodide) is essential to life.

Iodine in foods is converted to iodide in the gastrointestinal tract. In the body, the primary role of iodine involves thyroid function. Iodide is trapped by the thyroid gland, which uses it in the synthesis of the thyroid hormone thyroxin (T4). Thyroid hormones regulate body temperature, cell growth, metabolism and the formation of red blood cells, making iodine a mineral of great importance.

Iodine deficiency results in enlargement of the cells of the thyroid gland, a condition known as goiter. It can also cause sluggishness and weight gain, impaired fetal development, and cretinisim, a condition of severe mental retardation and stunted growth. Less severe forms of mental retardation may occur with iodine deficiency as well.

Throughout the world, iodine is added to salt to ensure adequate intakes of this important mineral. Most people are easily able to obtain sufficient amounts of iodine through consumption of iodized salt, which usually contains about 30-100 micrograms of iodine per gram.

The recommended amount of iodine for adults is about 150 micrograms per day. Children need between 70 and 150 micrograms of iodine per day, while pregnant women need 175 micrograms per day, and lactating women need 200 micrograms per day.

Since typical salt intake is 5-20 grams per day, people who use iodized salt easily meet iodine needs. Even when sodium intake is limited to the recommended 2 grams per day, iodine needs are easily met.

However, in areas where iodized salt is not available or for people who need to severely restrict sodium intake, iodine must be obtained from other sources. In addition, eating large amounts of plants in the cabbage family can compromise the absorption of iodine. These foods contain substances called goitrogens that bind iodine in such as way that the body cannot use it.

Some health care providers may recommend supplements of iodine under certain conditions. For example, iodine is used in topical ointments to treat wounds and burns, and it sometimes recommended for improving symptoms of fibrocystic breast disease. Though iodine is generally well tolerated and safe to consume through iodized salt and other foods, it is important to use iodine supplements with caution and under the guidance of a knowledgeable healthcare provider.

In some cases, too much iodine can damage the thyroid gland and lead to the development of goiter or hypothyroidism.

Excessive iodine intake is also associated with autoimmune disease and certain cancers.

People taking thyroid medications and those with thyroid disease, kidney disease or tuberculosis should be particularly cautious about the use of iodine supplements. In general, more than 2,000 micrograms of iodine per day is considered toxic. The usual amount of iodine consumed through iodized salt intake is 160-600 micrograms per day.

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