Iodine and selenium are two essential key nutrients that support thyroid function and are responsible for the synthesis of thyroid hormones. Iodine and selenium are trace minerals originating in soil. Soil content of iodine and selenium varies greatly due to erosion of exposed bedrock, farming practices and land development. Erosion of soil and bedrock leaches away iodine into the ocean. Seafood is one of the best sources of selenium and iodine.
Iodine
Iodized salt has played a major role in alleviating low levels of iodine in human diets in most parts of the world. Some underdeveloped areas are still at risk for low iodine if soil concentrations are low. The areas at risk are called goitrous areas because iodine deficiency will cause an enlarged thyroid gland called a goiter due to a low-functioning thyroid. Many people in goitrous areas have this problem because iodine is not available for synthesis of thyroid hormones. The recommended daily allowance (RDA) of iodine for adults is 150 μg, or micrograms, per day. You can easily get the RDA of iodine through food, especially if you eat seafood, sea vegetables, sea salt, eggs, milk and yogurt. Seafood is an excellent source of iodine with approximately 30 to 300 μg per 100 g, which equals a 3.5-ounce serving. Approximately ½ tsp. of sea salt provides the RDA, and 1 cup of milk or yogurt provides 60 to 80 μg of iodine. One egg provides 28 μg.
Selenium
Selenium is an essential trace mineral necessary for thyroid hormone regulation and the metabolism of iodine. Like iodine, it is found in varying concentrations in soil, which makes concentrations of selenium vary in plants and animals used for food. You likely get enough selenium through food if you eat a variety of seafood, meat and dairy products. People at risk of not getting enough selenium are those who are chronically ill or are being tube-fed. The RDA for selenium in adult men and women is 55 μg, or micrograms, per day. Seafood, like crab and salmon, is a good source of selenium with approximately 40 μg per 3 oz. Two slices of whole wheat bread have 23 μg of selenium, and 1 cup of milk has approximately 5 μg.
Other Nutrients
In addition to selenium and iodine, there are several other nutrients that help support your thyroid, especially a low-functioning thyroid. Omega-3 fatty acids found in salmon, sardines, flax seed and oil, whole grains and leafy green vegetables help alleviate inflammation. Tyrosine found in red meat, fish, almonds, avocado and pumpkin seeds helps with thyroid hormone production. Vitamin D found in cod liver oil, salmon, green leafy vegetables and fortified milk helps with the absorption of calcium, which is especially important when taking thyroid medications. Thyroid medications are known to leach calcium from the bones.
What to Avoid
Goitrogens are substances in food that block the absorption and metabolism of thyroid hormones. They naturally occur in certain foods such as raw peanuts, broccoli, cauliflower, kale, soybeans and soy products and strawberries. Cooking destroys the goitrogen compounds in vegetables. Roasting peanuts also inactivates goitrogens, making peanut butter possible for you to eat if you have a low-functioning thyroid. Two to three servings per week of broccoli, kale, cauliflower or other cruciferous vegetables appear to be tolerated by those with a low-functioning thyroid. Cruciferous vegetables belong to the Brassica family, which includes broccoli, cauliflower, spinach, Brussels sprouts, cabbage, rutabaga, kohlrabi and turnips.
References
- "Advanced Nutrition and Human Metabolism, Fifth Edition"; Sareen Gropper et al; 2009
- "Food and Nutrients in Disease Management: Hypothyroidism"; S. Tenpenny; 2009
- Linus Pauling Institute; Micronutrient Information Center - Iodine; March 2010
- Linus Pauling Institute; Micronutrient Information Center - Selenium; 2007
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