Foods Which Reduce Thyroid Function

Foods that reduce thyroid function are called goitrogens. They have this name because of their potential to enlarge the size of the thyroid gland, which is a condition clinically identified as goiter. Goitrogens, according to the Linus Pauling Institute, interfere with the way iodine is used by the thyroid gland. Iodine is essential for the production of thyroid hormones. Goiters develop as the cells of the thyroid gland hypertrophy, or enlarge, in an attempt to produce more of the hormones in which they have become deficient.

Cruciferous Vegetables

Cruciferous vegetables include broccoli, cabbage, collard, kale and mustard greens, cauliflower and Brussels sprouts. These foods have recently been touted as superfoods because of their antioxidant profiles and cancer-fighting potential, however, this family of vegetables is also known for its goitrogenic qualities. The Linus Pauling Institute notes that goitrogens are especially problematic in the face of an iodine deficiency. A 2010 "Cancer Causes & Control" article finds that in areas with endemic goiters, or goiters caused by iodine-deficiency, an increased consumption of cruciferous vegetables can increase one's risk of thyroid cancer. However, goitrogens from cruciferous vegetables can be reduced by steaming or cooking them as their concentration is the highest when raw.

Cassava

Cassava is a tropical plant, also commonly known as yucca. This starchy vegetable is a staple food of African countries like Nigeria and it is also eaten in the Caribbean, South America and many southeast Asian countries. The Linus Pauling Institute lists cassava as a goitrogen. A 2007 "Sante" article notes that cassava contains a chemical known as thiocyanate, which blocks iodine uptake and interferes with thyroid hormone production. The writers find that in sub-Saharan Africa, as in many other areas in the world, an iodine deficiency is common. Because there is a persistent iodine-deficiency problem in African countries coupled with consumption of this common goitrogenic staple, many women and children develop a variety of thyroid diseases and as a result suffer from delayed physical and mental development and death. It was noted that the milling of cassava reduced its goitrogenic potential.

Millet

Millet is a cereal crop that is most commonly seen as the yellowish, round seed of bird feed. However, this grain is also served and consumed around the world as a cereal grain and side dish. The 2007 "Sante" journal article notes that it also acts as a goitrogen in the body. The article reports that millet contains two substances, apigenin and luteolin, which can interfere with thyroid hormone production.

Soy

Soy is another common food known for its deleterious effects on the thyroid. Soy isoflavones, are noted by a 2002 "Environmental Health Perspectives" article to be both estrogenic and goitrogenic. The article warns of the cumulative effect that soy products may have on human and animal thyroid health. They further note that the relationship may not only be present in the face of an iodine deficiency, but other soy components and other hormone issues could further exacerbate the problem.

Tobacco

Smoking tobacco is a risk factor for many diseases, and a relationship between cigarette smoking and goiter development has been noted, according to a 2002 "Thyroid" article. Accordingly, the researchers conclude that tobacco competitively inhibits the ability of the thyroid cells to uptake iodine and create their respective hormones. This effect is worsened when an iodine deficiency existed preliminarily.