Your thyroid gland produces hormones essential to the normal functioning of metabolism, growth, development, reproductive function and other physiologic processes. Hypothyroidism occurs when the thyroid gland fails to meet the body’s demand for thyroid hormones, causing symptoms in your body that range from uncomfortable to life threatening. Hypothyroidism may develop in people who suffer from autoimmune diseases, take certain medications or undergo cancer treatments, such as chemotherapy and radiation therapy. Eating extremely large amounts of certain vegetables, such as Brussels sprouts can affect thyroid function. Therefore, people with already impaired thyroid function should avoid Brussels sprouts and other cruciferous vegetables.
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Brussels sprouts contain several classes of goitrogens, which suppress thyroid hormone production. People with low thyroid hormone production are at risk of thyroid disease, including hypothyroidism. Goitrogens can be generated enzymatically from the hydrolysis of some glucosinolates, sulfur-rich plant metabolites, found in Brussels sprouts and other Brassica vegetables. However, many nutritionists believe that these goitrogens are deactivated by processing and cooking.
Some species of cruciferous vegetables, including cabbage, broccoli and Brussels sprouts, contain a compound called indole glucosinolates that are metabolized to thiocyanate ions to prevent the uptake of iodine by the thyroid gland. Your body needs iodine to produce thyroid hormones. Thus, people consuming high amounts of Brussels sprouts are at risk of developing iodine-induced hypothyroidism. You can easily offset this effect by increasing the amount of iodine in your diet.
There is a published case report of hypothyroidism with bok choy -- a Chinese cabbage. A 88 –year-old woman developed hypothyroidism and coma upon consuming 1.0 to 1.5 kg of raw bok choy daily for a few months.
In a study, eating 150 g, or 5 oz, of cooked Brussels sprouts each day for four months did not affect thyroid function.