by Reed Mangels, PhD, RD
A reader contacted us to ask if cruciferous vegetables inhibit iodine absorption. To answer this question, it’s important to know a little about why we need iodine and what cruciferous vegetables are.
Iodine is an essential mineral that is used by the thyroid gland to make thyroid hormones. These hormones play an important role in controlling metabolism and are needed for infant and child development. Vegans get iodine from iodized salt, sea vegetables, dietary supplements, and to some extent, from plant foods. The iodine content of plant foods depends on factors such as the concentration of iodine in the soil where the plants were grown (1). When foods or supplements containing iodine are used, the iodine is absorbed and transported in the blood to the thyroid gland.
Cruciferous vegetables are what we think of as the cabbage family and include broccoli, Brussels sprouts, cauliflower, kale, kohlrabi, and cabbage. These vegetables, along with soy, beans, sweet potatoes, cassava, and some other foods, contain substances called goitrogens that interfere with the thyroid gland taking up iodine from the blood. This could lead to a reduced production of thyroid hormones.
According to several authoritative sources, goitrogens are mainly a problem for people who do not have an adequate amount of iodine in their diet or for those who consume large amounts of these foods (2-4), especially in raw form (5). Large amounts mean, for example, a diet which is based mainly on cassava. A recent review concluded that cruciferous vegetables “are safe for thyroid function, especially when the proper iodine supply is provided” (4).
It’s important to have an adequate intake of iodine, which for vegans probably means using iodized salt and/or taking a supplement that contains iodine (6). With an adequate intake of iodine, it’s unlikely that eating cruciferous vegetables will interfere with iodine uptake by the thyroid gland.
To read more about getting adequate iodine on a vegan diet see:
References
- Ershow AG, Skeaff SA, Merkel JM, Pehrsson PR. Development of databases on iodine in foods and dietary supplements. Nutrients. 2018;10(1):100.
- National Institutes of Health. Office of Dietary Supplements. Iodine. Fact sheet for health professionals. https://ods.od.nih.gov/factsheets/Iodine-HealthProfessional/. 2024.
- Oregon State University, Linus Pauling Institute, Micronutrient Information Center. Iodine. https://lpi.oregonstate.edu/mic/minerals/iodine. 2024.
- Institute of Medicine, Food and Nutrition Board. Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc. Washington, DC: National Academy Press, 2001.
- Galanty A, Grudzińska M, Paździora W, et al. Do brassica vegetables affect thyroid function?-A comprehensive systematic review. Int J Mol Sci. 2024;25:3988.
- Mangels R. Am I getting enough iodine? Vegan Journal. 2024, Issue 3.
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