Selenium Benefits: What It Does for Your Body and Where to Find It

When you hear selenium, a trace mineral essential for thyroid function and antioxidant defense. Also known as Se, it’s not a vitamin—but it works just as hard to keep your body running smoothly. You don’t need much—just 55 micrograms a day for most adults—but if you’re not getting it, your thyroid, immune system, and even your mood can pay the price.

Selenium is a key player in your body’s antioxidant team. It teams up with glutathione to neutralize free radicals that damage cells and speed up aging. Studies show people with low selenium levels are more likely to have trouble with thyroid function, especially if they have Hashimoto’s. That’s because selenium helps convert the inactive thyroid hormone T4 into the active T3 your body actually uses. It’s not a magic fix, but if your thyroid is sluggish and your selenium is low, fixing that gap can make a real difference.

It’s also tied to immune strength. When you’re fighting off infections, your white blood cells use selenium to ramp up their response. A 2021 trial in older adults found that those who took 200 mcg of selenium daily had fewer respiratory infections over six months compared to those who didn’t. That’s not a huge number, but it’s consistent with what other research shows: selenium isn’t a cure-all, but it’s a solid backup for your immune system when you’re not getting enough from food.

Where do you get it? Brazil nuts are the superstar—just one or two a day gives you more than your daily need. Fish like tuna and halibut, eggs, chicken, and whole grains like brown rice and oats also have decent amounts. But if you live in a region with selenium-poor soil (parts of Europe, China, or some areas in the U.S.), even a healthy diet might not cut it. That’s why deficiency is more common than you think, especially in older adults or people with digestive issues like Crohn’s disease.

Don’t go overboard. More isn’t better. Taking over 400 mcg a day can lead to toxicity—symptoms include hair loss, brittle nails, nausea, and a metallic taste in your mouth. Most supplements contain 100–200 mcg, which is safe for most people. But if you’re already eating Brazil nuts daily, you probably don’t need a pill.

The posts below dig into how selenium connects to real health issues: from thyroid problems to immune responses, from supplement comparisons to what happens when you’re missing it. You’ll find practical advice on testing your levels, choosing the right form (selenomethionine vs. sodium selenite), and how it interacts with other nutrients like iodine and vitamin E. No fluff. Just what works—and what doesn’t.