Selenium: what it does, how much you need, and how much is too much
By Vita · fact-checked against NIH ODS
Vita is Vitaminico's AI nutrition coach. Every number here is checked against the NIH Office of Dietary Supplements; these pages have not yet been reviewed by our registered dietitians.
An essential trace mineral your body uses to build protective antioxidant enzymes.
Selenium: key facts
- Everyday need (RDA/AI)
- 55 mcg for all adults (60 mcg in pregnancy, 70 mcg in lactation)
- Safe upper limit (UL)
- 400 mcg
- Measured in
- mcg
- Best foods
- Brazil nuts, seafood (tuna, shrimp), meat, poultry, organ meats, eggs, whole grains
Adult values from the NIH ODS Selenium fact sheet. Needs differ in pregnancy, lactation and childhood.
What does selenium do?
Selenium is a trace mineral your body builds into proteins called selenoproteins, which act as antioxidant enzymes that shield your cells from everyday damage. It's also needed to make and regulate thyroid hormones, and it supports a healthy immune system and normal reproduction. You only need a tiny amount, and most people get enough from a normal diet.
Why you might be low on selenium
- You eat mostly plant foods grown in low-selenium soil (common in parts of China, Russia, and some regions of Europe) and eat mainly local produce
- You're on kidney dialysis, which lowers selenium levels
- You're living with HIV
- You have a severe digestive disorder such as Crohn's disease, or have had gut surgery, that reduces how much you absorb
Signs of low selenium
These are common signals, not a diagnosis — a blood test and your clinician confirm a real gap.
- Keshan disease — an enlarged, weakened heart, historically seen in selenium-deficient children in low-selenium regions
- Kashin-Beck disease — a joint and bone disorder (a form of osteoarthritis)
- Possible reduced fertility in men
- Worsening of an existing iodine deficiency and its effects on the thyroid
- Note: on its own, deficiency rarely causes obvious symptoms — it mainly makes the body more vulnerable to other stresses and infections
Best food sources of selenium
| Food | Typical amount |
|---|---|
| Brazil nuts (dried, unblanched) | 544 mcg per 1 oz (about 6-8 nuts) |
| Yellowfin tuna (cooked) | 92 mcg per 3 oz |
| Halibut (cooked) | 47 mcg per 3 oz |
| Sardines (canned in oil, drained) | 45 mcg per 3 oz |
| Shrimp (cooked) | 42 mcg per 3 oz |
| Beef steak (cooked) | 33 mcg per 3 oz |
| Egg (hard-boiled) | 15 mcg per 1 large egg |
How much selenium is too much?
The tolerable upper intake level (UL) for adults is 400 mcg per day. Chronic excess (selenosis) causes hair and nail brittleness or loss and a garlic breath odor; note a single Brazil nut can supply a full day's requirement.
The adult upper limit is 400 mcg per day, and going over it regularly — usually from overdoing supplements or eating Brazil nuts every day — can cause selenosis: garlic-smelling breath, a metallic taste, hair loss, brittle nails, skin rash, nausea, and fatigue. Very high doses can lead to serious stomach and nervous-system problems.
Stacking a multivitamin, a single supplement and fortified foods adds up faster than it looks — run your full dose through the free Supplement Safety Checker before adding anything new.
Selenium FAQ
Should I eat Brazil nuts every day to get selenium?
Better not to. Just one Brazil nut can supply more than a full day's requirement, and a small daily handful can push you toward the 400 mcg upper limit. Enjoy them occasionally, or stick to one or two nuts.
Do I need a selenium supplement?
Most people in the US and Canada get plenty from food, so a supplement usually isn't needed. They mainly help people with specific issues like severe digestive disorders, dialysis, or intravenous feeding — check with a doctor before taking one.
How much selenium do I need per day?
Adults need 55 mcg a day; that rises to 60 mcg in pregnancy and 70 mcg while breastfeeding. Children need less, from about 20 mcg (ages 1-3) up to 40 mcg (ages 9-13).
Source
Every RDA/AI, upper limit and unit on this page is drawn from the NIH Office of Dietary Supplements Selenium fact sheet ›.
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Educational, not medical advice. The upper limits shown are Tolerable Upper Intake Levels for healthy adults from all sources combined; needs differ in pregnancy, lactation, childhood and with some conditions or medications. This page does not diagnose a deficiency or set your dose — talk to your clinician before starting any high-dose supplement.