Goitrogens are substances which cause the thyroid gland to be unable to process iodine correctly and affect its ability to create hormones. When iodine uptake is blocked by these agents, the gland can swell, creating a mass in the neck called a goiter. There are a variety of foods that have goitrogenic properties. Certain drugs and other chemicals may also interfere with the thyroid's ability to deal with iodine. A goiter is not necessarily caused solely by the ingestion of goitrogens, particularly those from foods, but those with impaired thyroid function may want to avoid them as they can make a goiter more likely to occur.
There are several foods which contain naturally occurring goitrogens. Soybeans and soy products such as tofu are some of the main types of food that can decrease the function of the thyroid gland. They contain isoflavones, a type of phytonutrient that blocks iodine processing, which in turn decreases thyroid hormone production. Isoflavones are generally considered to be good for the health, but their goitrogenic properties may make them less than ideal for those with impaired thyroid function.
Cruciferous vegetables like broccoli, cauliflower, and Brussels sprouts also contain goitrogens. In these plants, which are all in the genus Brassica, the substances that affect the thyroid are called isothiocyanates. Other vegetables in this family with goitrogenic properties include turnips, kale, and cabbage.
Several other foods are also considered to be mild goitrogens. Fruits like strawberries, peaches, or pears may affect the thyroid. Pine nuts, peanuts, and millet may also be goitrogenic; spinach and sweet potatoes also fall into this category. Those eating these foods, as well as soy or crucifers, should mainly be concerned if they are consuming them raw; cooking them destroys the goitrogens and thus negates their effects. In general, the level of goitrogens in these foods is not enough to cause a goiter in a healthy individual, and even those with hypothyroidism can consume them in moderation but should avoid overconsumption.
Some drugs can impact thyroid function and lead to the development of a goiter. Use of amiodarone to treat an irregular heartbeat can lead to hypothyroidism and goiter. Lithium, often taken for psychiatric disorders such as bipolar, may decrease thyroid hormone production. Anticonvulsants like carbamazepine and phenobarbitone may also affect hormone levels. Certain hyperthyroid medications like propylthiouracil, methimazole, and potassium perchlorate are specifically used to decrease thyroid function and could potentially be goitrogenic in excess.