What it does
The amount in plant foods depends strongly on soil, so food content can vary. Deficiency is uncommon in many regions but may occur in specific geographic or medical contexts.
Food sources and absorption
Seafood, meat, poultry, eggs, dairy, grains, and Brazil nuts can contribute. Brazil nuts may contain very high and variable amounts, so a large daily handful is not a precise supplement strategy.
Safety and individual context
Chronic excess can cause hair and nail changes, gastrointestinal symptoms, and neurologic problems. Selenium has a Tolerable Upper Intake Level; avoid stacking multiple supplements without checking totals.
Primary reference
NIH Office of Dietary Supplements consumer fact sheet
How to use this information
Reference values describe population needs and are not a diagnosis. Food patterns, health conditions, pregnancy, laboratory results, and medications can change what is appropriate. Avoid high-dose supplementation unless there is a clear reason and qualified guidance.