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Health & Fitness What should you eat (and avoid) if you have low thyroid?

Q: I’ve been diagnosed with low thyroid and have started taking medication. Are there certain foods that I can eat to help my thyroid? Any foods that I should avoid?

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Your thyroid gland relies on several nutrients to function properly. Minerals such as iodine and selenium, for example, are essential for making thyroid hormones.

While good nutrition is important for thyroid health, diet and supplements are not a replacement for thyroid medication. And if you have hypothyroidism (low thyroid), there are some foods and supplements that you need to be cautious about.

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Low thyroid 101

The thyroid gland, located at the front of the neck, makes and stores thyroid hormones which affect nearly every organ in the body. Called triiodothyronine (T3) and thyroxine (T4), thyroid hormones regulate the speed of your metabolism, body temperature, cell growth, brain development, cholesterol levels, blood calcium levels and much more.

When the thyroid gland doesn’t produce enough thyroid hormones, hypothyroidism results. Symptoms include unexplained weight gain, constipation, fatigue, hair loss, dry skin, intolerance to cold, difficulty concentrating, joint pain and menstrual-cycle changes.

People of any age can develop hypothyroidism, but older adults are more likely to get it, especially older women. If the condition runs in your family, you also have a higher risk.

In Canada, the most common cause of hypothyroidism is Hashimoto’s thyroiditis, an autoimmune disorder in which the body’s immune system attacks the thyroid gland reducing its ability to make thyroid hormones.

Once the body can no longer produce an adequate amount of thyroid hormones to support its functioning, thyroid replacement medication is necessary.

Nutrition for thyroid function

Iodine, a mineral found in iodized table salt, fish and seafood, dairy products, grains and seaweed, is an essential component of thyroid hormones. People who don’t consume enough iodine are at risk for developing hypothyroidism.

Adults need 150 mcg of iodine each day for normal thyroid function. Pregnant women require 220 mcg daily and are advised to take a multivitamin and mineral supplement containing 150 mcg of the mineral to ensure proper development of a baby’s brain and nervous system.

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Getting too much iodine can also harm thyroid function. Avoid consuming excess iodine (e.g. supplements, seaweed products), which can worsen hypothyroidism.

Selenium is a vital component of enzymes involved in the synthesis of thyroid hormones. The mineral also acts as an antioxidant, protecting thyroid tissue from harmful free radical molecules.

The daily recommended intake of selenium is 55 mcg for women and men. Excellent sources include Brazil nuts (1 nut has 95 mcg), tuna, halibut, sardines, shrimp, beef, turkey, cottage cheese, brown rice and eggs.

Consuming too much selenium can be toxic; the safe upper limit from foods and supplements is 400 mcg a day.

Zinc also plays a role in making thyroid hormones. It’s found in oysters, beef, crab, pork, chicken, pumpkin seeds, cashews, chickpeas, yogurt, milk and fortified breakfast cereals.

Foods that may disrupt the thyroid

Naturally occurring compounds in some foods are considered goitrogens, which means they can interfere with the production of thyroid hormones.

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Compounds in cruciferous vegetables (e.g. bok choy, broccoli, Brussels sprouts, cauliflower, cabbage, collard greens, kale, turnip) called thiocyanates, for example, can reduce the uptake of iodine in the thyroid. Eating too much of these vegetables is considered only a concern for people who have an iodine and/or selenium deficiency, which is uncommon in North America.

Still, if you have an underactive thyroid, it’s wise to avoid juicing cruciferous vegetables since it concentrates the amount of goitrogens. Cooking cruciferous vegetables, even lightly steaming them, deactivates goitrogens.

Isoflavones in soy foods such as tofu, soy milk, edamame and miso can also reduce thyroid hormone synthesis. But, again, studies have found that this does not affect people with adequate iodine stores.

Studies in the 1980s found that pearl millet, a gluten-free grain, was goitrogenic, even in people who were not iodine deficient. Much of the millet sold in North American is proso millet, which has not been shown to be goitrogenic.

If millet and millet products are your staple grain products, call the manufacturer to find out which type of millet is used.

Time supplements around medication

Calcium, iron and chromium supplements interfere with the proper absorption of thyroid replacement medication. So can antacids that contain calcium, magnesium and aluminum.

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Space these products four hours apart from thyroid medication.

Fibre supplements may reduce the absorption of thyroid medication; it’s best to take them one hour apart.

If you’re unsure about other supplements or medications that my interfere with your thyroid medication, speak to your pharmacist.

Leslie Beck, a Toronto-based private practice dietitian, is Director of Food and Nutrition at Medcan.

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