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11 Selenium-Rich Foods for Thyroid Health and Immunity

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  Published in Food and Wine on Sunday, October 5th 2025 at 7:18 GMT by Today
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Selenium‑Rich Foods: What You Need to Know About This Essential Trace Mineral

Selenium is a trace mineral that is essential for human health, yet many people don’t realize how vital it is or how easily they can miss it in their diets. A recent Today.com feature – “Selenium‑Rich Foods” – dives into what selenium does, why it matters, and which foods give you the best bang for your buck. Below is a comprehensive 500‑plus‑word overview that pulls together the key points from the article and expands on them with additional research and background information found on the linked pages.

1. What Is Selenium and Why Is It Important?

Selenium is a mineral found in the earth’s crust that the body needs in minuscule amounts—about 55 µg per day for adults, according to the National Institutes of Health (NIH). Despite the small quantity, it performs several critical functions:

• Antioxidant defense – Selenium is a core component of glutathione peroxidase and thioredoxin reductase, two enzymes that neutralize harmful free radicals.
• Thyroid hormone metabolism – Selenium‑containing deiodinases convert the pro‑thyroid hormone T4 into the active T3 form.
• Immune system support – Adequate selenium levels enhance both innate and adaptive immune responses.
• Potential cancer protection – Some studies suggest that selenium may lower the risk of certain cancers, such as prostate, colorectal, and lung cancer, though results are mixed and the evidence is not yet conclusive.

In contrast, selenium deficiency can lead to Keshan disease (a cardiomyopathy seen in China) and other health issues such as fatigue, hair loss, and impaired immune function.

2. How Much Selenium Should You Aim For?

The Recommended Dietary Allowance (RDA) for adults is 55 µg daily. The Tolerable Upper Intake Level (UL) is set at 400 µg per day, because too much selenium can cause selenosis—a condition characterized by gastrointestinal upset, hair loss, fatigue, and, in extreme cases, neurological damage.

Because the selenium content in foods varies by soil composition, the best way to stay within healthy limits is to diversify your sources and avoid excessive supplementation unless directed by a healthcare professional.

3. The Top Selenium‑Rich Foods

Below is a rundown of the highest‑yielding selenium foods, including approximate selenium content per common serving size. All values are sourced from the USDA FoodData Central database and the Today.com article.

Why Brazil nuts are king – Brazil nuts absorb selenium from the soil, making them a highly efficient source. A single nut can supply more than the daily requirement for some people, so moderation is key.

4. How to Incorporate Selenium Into Your Diet

1. Add a handful of Brazil nuts as a snack, but limit yourself to no more than 2–3 nuts per day to stay below the UL.
2. Include seafood like tuna, salmon, or shrimp a couple of times a week. Try grilled or baked preparations to keep calories in check.
3. Use eggs in breakfast dishes or as part of salads. A half‑egg equivalent can add significant selenium without a huge caloric impact.
4. Choose whole‑grain products such as whole‑wheat bread, oatmeal, or brown rice, especially if grown in selenium‑rich soil.
5. Rotate different proteins – poultry, beef, and legumes all contribute, albeit in smaller amounts.
6. Explore mushrooms – Shiitake and button mushrooms can be sautéed into dishes for an extra selenium boost.

5. The Good and the Bad: Selenium’s Health Implications

6. Where to Learn More

The Today.com article links to several deeper dives that broaden the discussion:

• Selenium deficiency: Symptoms and treatment – Offers a clinical view of how low selenium affects body systems and when supplementation is warranted.
• Selenium and thyroid function – Reviews how the mineral influences thyroid hormone metabolism and what that means for patients with hypothyroidism or hyperthyroidism.
• Selenium and cancer risk – Summarizes the meta‑analyses and clinical trials that examine whether higher selenium intake correlates with reduced cancer mortality.
• Selenium in pregnancy – Highlights the importance of adequate selenium for fetal development and maternal health, especially in populations with low soil selenium.

7. Bottom Line

Selenium is a tiny mineral with a big impact—protecting cells from oxidative damage, enabling thyroid hormone activation, and possibly playing a role in cancer prevention. The healthiest way to keep your levels in check is to enjoy a varied diet that includes Brazil nuts (in moderation), seafood, eggs, whole grains, legumes, and mushrooms. While supplements are available, the evidence does not support their routine use in healthy adults, and excess intake can be harmful.

In short, a balanced diet that naturally includes selenium‑rich foods is your safest and most effective strategy for harnessing this essential nutrient’s full health benefits.