Selenium — what it does, where to get it, and how to take it safely
Selenium is a trace mineral you need in tiny amounts, but it matters. It helps antioxidant enzymes work, supports the immune system, and plays a role in thyroid hormone metabolism. You don’t need grams of it — micrograms are enough — but both too little and too much cause problems. Below are practical, no-nonsense tips on food, dosing, signs of trouble, and choosing a supplement when needed.
What selenium does and where to get it
Your body uses selenium mainly inside selenoproteins. These protect cells from oxidative damage and help convert thyroid hormone T4 into the active T3. Common foods high in selenium: one Brazil nut (about 68–90 mcg on average) often covers an adult’s daily need; 3–4 oz of tuna or half a cup of cooked brown rice also provide useful amounts. Other good sources: shrimp, sardines, organ meats, eggs, and fortified cereals. Soil selenium varies by region, so plant foods can differ a lot in content.
Recommended daily amounts: adults typically need about 55 mcg/day, pregnant people about 60 mcg, and breastfeeding about 70 mcg. The tolerable upper intake level for adults is 400 mcg/day — avoid long-term intake above that unless a doctor advises otherwise.
Watch for deficiency signs: fatigue, weak nails, hair loss, and in severe cases, impaired immune function or thyroid issues. Deficiency is uncommon in countries with selenium-rich soils but can occur with restrictive diets, certain digestive disorders, or long-term parenteral nutrition.
How to use supplements safely
If your diet gives you enough selenium, you probably don’t need a supplement. Test your need first: a blood or plasma selenium test and a doctor’s evaluation can help, especially if you have thyroid disease or fertility concerns. When supplements make sense, choose the right form. Selenomethionine has higher absorption and is common in capsules. Sodium selenite and selenate are also used but behave differently in the body; follow label dosing.
Keep doses sensible. A typical supplement dose is 50–200 mcg/day. Stay below the 400 mcg/day upper limit unless under medical supervision. Signs of too much (selenosis) include a metallic taste, bad breath, hair or nail brittleness, and nerve symptoms. If you take high-dose selenium with other antioxidants or medications, tell your clinician — interactions are uncommon but possible.
Special notes: some clinical trials suggest selenium supplements can reduce thyroid antibody levels in autoimmune thyroiditis for some people, but results vary. There’s limited evidence that selenium may help sperm quality in men with low selenium. Don’t start high-dose supplements to chase vague benefits — get tested, talk to your provider, and focus on food first.
Practical picks: if you want a low-risk option, take a 55–100 mcg daily selenomethionine supplement for a short trial and recheck blood levels after 3–6 months. Prefer whole foods over pills when possible — one Brazil nut a day is a simple, effective choice for many people.
