Nutrient glossary
What is selenium?
Selenium fuels antioxidant enzymes and thyroid hormone conversion; two brazil nuts cover a day.
Reviewed 20 July 2026. General information, not medical advice.
The short version
Selenium slots into proteins that protect cells from oxidative damage, convert thyroid hormone into its active form and support sperm production. UK soils are relatively low in it, so intakes here run closer to the line than in North America.
Brazil nuts are famously dense, one or two nuts can cover the day, and fish, meat, eggs and wholegrains carry the rest.
Daily reference
75 µg a day
The reference is 75 µg a day for men and 60 µg for women. The safe upper level is a few hundred µg, which a large daily handful of brazil nuts can approach, so treat them as a couple-a-day food.
This is the fixed adult reference used across these pages. In the app, your amount adjusts to your body and way of eating.
Best food sources of selenium
Full ranking| Food | Per serving | Per 100g |
|---|---|---|
| Brazil Nuts | 384 µg | 1,920 µg |
| Tuna Steak | 140 µg | 108 µg |
| Mussels | 90 µg | 90 µg |
| Tuna (canned) | 84 µg | 70 µg |
| Halibut | 78 µg | 55 µg |
| Lobster | 73 µg | 73 µg |
| Tilapia | 65 µg | 54 µg |
| Salmon Fillet | 62 µg | 41 µg |
Common questions
- How many brazil nuts should I eat a day?
- One to three covers the reference comfortably. A large daily handful every day risks overshooting the safe upper level over time.
- Does selenium support the thyroid?
- Yes, the enzymes that activate thyroid hormone are selenium-dependent, which is why adequate intake matters for normal thyroid function.