Whether or not cruciferous vegetables are linked to hypothyroidism has been a hot topic recently in the medical world. As we all know there is a lot of misconstrued information regarding nutrition on the internet so I feel it is important to explore this topic further with the latest evidence-based information and how cruciferous vegetables can be a part of a well balanced diet.
Before we dive in, it’s important to understand what the thyroid does for the body. The thyroid produces hormones that play a vital role in the metabolism and growth of the body. When the body has increased energy needs such as being cold or during pregnancy, the thyroid releases more hormones. The thyroid produces three different types of hormones: T3 or Triiodothyronine and T4 or Tetraiodothyronine (also known as thyroxine) which work together to promote growth and brain development in children, raise body temperature, activate the nervous system, and help the heart beat stronger and faster when necessary. The third hormone, calcitonin, is involved in bone and calcium metabolism.
Iodine is an essential trace mineral, which our bodies cannot produce and must come from dietary sources. It is a key component in the production of the T3 and T4 hormones. Iodine can be found in iodized salt, eggs, dairy, saltwater fish, shellfish, soy sauce, and soy milk. Processed foods which contain excess sodium, such as frozen dinners and deli meats, often do not provide iodine. One teaspoon of iodized salt contains 400 μg of iodine and is considered to be the best source in preventing deficiency. Iodine deficiency still affects 40% of the world’s population but has dramatically decreased in the US since the 1920s. Iodine deficiency can create goiters (enlargement of the thyroid gland), hypothyroidism1, and mental retardation in children of pregnant women who may be iodine deficient. Hypothyroidism caused by iodine deficiency is most common worldwide.1 However, another type of hypothyroidism is Hashimoto’s and is most commonly seen in the US.3 Hashimoto’s is an autoimmune disorder where the body creates antibodies that attack the thyroid gland causing a drop in the production of thyroid hormones. The recommended dietary allowance (RDA) for iodine set by the Institute for Medicine is 150 μg for adult men and women. For pregnant and breastfeeding women, the RDA is 220-290 μg. However, just like anything else, you can have too much of a good thing. For this reason, unless prescribed by your doctor for medical reasons, it is not recommended to take an iodine supplement as this can sometimes make thyroid conditions worse.
What does this have to do with cruciferous vegetables? Some suggest this group of vegetables are linked to hypothyroidism. Some of the more common cruciferous vegetables include brussel sprouts, broccoli, cabbage, kale, radishes, turnips, and cauliflower. These vegetables are also considered goitrogens. Goitrin, a natural chemical compound released from cruciferous vegetables when broken down, is really only a concern for those who have an iodine deficiency, a condition that as I mentioned earlier is fairly rare these days, and consume the vegetables raw or via juicing. Goitrin can interfere with the production of thyroid hormones by making it more difficult for the uptake of iodine in the thyroid to produce T3 and T4. When cooked, these cruciferous vegetables have most if not all of their goitrogenic effects denatured and pose no risk to thyroid health.
In fact, cruciferous vegetables have also been studied for their anti-cancer effects for certain forms of cancer as they are rich in antioxidants and phytochemicals. These natural components have been shown to inactivate carcinogens, induce cell death, inhibit tumor blood vessel formation, and have anti-inflammatory effects. Cruciferous vegetables are also very high in other vitamin and minerals as well as fiber which can help prevent constipation as a lot of those with hypothyroidism tend to experience. Given the benefits of cruciferous vegetables outweighs the minimal risk on thyroid health, they can be considered an important part of a well balanced diet.
- American Thyroid Association. Iodine Deficiency. https://www.thyroid.org/iodine-deficiency/
- PubMed Health. How does the thyroid work? https://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0072572/
- American Thyroid Association. Hashimoto’s Thyroiditis. https://www.thyroid.org/hashimotos-thyroiditis/