Goitrogens are foods, drinks, or inhaled substances that prevent the body from using iodine and making the thyroid hormones. If these substances are regularly ingested, the thyroid gland is forced to work harder and harder to compensate for inadequate hormone production. This leads to it becoming enlarged, and forming a “goitre”.
How do Goitrogenic Foods Block Iodine from the Body?
The main type of goitrogenic foods are those that liberate large quantities of toxic cyanide. The cyanide metabolite, thiocyanate, then forms within the body and interferes with iodine uptake by the thyroid gland. However, the glycosides that release cyanide – the toxic parts – are usually located in the inedible portions of the plants. When they do occur in the edible portions, they tend to exist in much smaller quantities. The only exception is cassava, where glycosides are located in the edible part of the plant.
Which Foods are Goitrogenic?
Many goitrogens grow and are staple foods in developing countries, such as cassava, maize, sweet potatoes, bamboo shoots, pearl millet, and lima beans. They often grow in areas that are also iodine deficient, which increases the likelihood of goitre.
Other common foods that are goitrogenic include: spinach, broccoli, brussel sprouts, cabbage, kale, cauliflower, horseradish, mustard greens, rutabaga, turnips, kohlrabi, radishes, peanuts, and rapeseed oil.
What about Soy?
Soybeans were first shown to be goitrogenic in the 1930s (1), inhibiting the formation of thyroxine. Soy’s goitrogenic action is due to its isoflavones, which appear to block the action of a thyroid enzyme. Isoflavones are types of flavonoids – the pigments that give plants their colours – and they are generally praised for their health benefits. But the link between this one particular sort (isoflavones) and thyroid dysfunction is detrimental to health.
The fermentation process of soy may lessen its goitrogenic effect, but anyone with an existing goiter should probably avoid soy where possible. Check any vitamin supplements for inclusion of soy; vitamin E capsules very often contain soya oil.
Is it Okay to Eat Goitrogenic Foods?
Eating small amounts of goitrogenic foods, especially if cooked, is unlikely to be a problem for most people – even those with goitres. The cooking process seems to lower their goitrogenic activity, as does juicing (compared to eating them raw). Recent research suggests that even cassava – the plant with the highest glycosides – reduces in cyanide metabolite after going through the milling process.
Is it True that Smoking Can Cause a Goitre?
Smoking tobacco releases a metabolite of hydrogen cyanide gas into the body fluids, and this acts as a thiocynate, inhibiting the iodine-conversion mechanism of the body. Cigarette smoke not only contains thiocyanate, but also a variety of goitrogenic derivatives. In fact, cigarette smoking is thought capable of causing goitre without any other factor involved, and studies indicate that it increases the severity of any hypothyroidism, through the way it alters both thyroid function and hormone action.
What Else Can Cause Goiters?
It is estimated that around 200 million people around the world have thyroid goiters (2), and the key factor in goiter growth is iodine deficiency. Ironically, excess iodine intake, from eating iodine-rich food, such as seaweed (especially dulse and kelp) can also cause goitres.
Dietary factors (such as the cyanogenic glucosides and flavonoids listed above) are another common cause, as are autoimmune diseases such as Hashimoto’s autoimmune thyroiditis and Graves’ disease. Environmental exposure to specific goitrogens (in polluted wastewater, for example) can cause goiters, as can certain medicines, such as lithium. Infection from a number of bacteria, parasites, and fungi, are also known to cause goiters.
Is There a Treatment for Goiters?
Goitrogenic activity can be overcome by iodine supplementation where goitres have been caused by iodine deficiency. However, people with Hashimoto’s disease should not increase iodine intake, as this can worsen the disease and its effects, leading to an increase in size of any goiter. Administration of Levothyroxine (used to treat hypothyroidism) can also be used in Hashimoto’s patients to treat goiters.
Read More:
Iodine and Hashimoto’s Thyroiditis
Minerals and Supplements for Hashimoto’s Disease
The Truth About Hashimoto's
REFERENCES
1 “Diseases of the Thyroid”; Lewis E. Braverman, Humana Press, 2003, p.310.
2 Ibid.
