CWeak evidence, or evidence againstMineral
The short answer
Almost nobody eating a varied diet needs this, and the safety margin is tight enough that guessing is a bad idea.
Who this is actually for
People in genuinely selenium-poor regions or with malabsorption.
What it is legally allowed to claim
Quoted from the EU register of authorised health claims, Regulation (EU) 432/2012. A product may only make these claims if it supplies enough of the nutrient to qualify.
- Selenium contributes to the normal function of the immune system
- Selenium contributes to the protection of cells from oxidative stress
How much is too much
EFSA tolerable upper intake level 255 micrograms per day for adults, revised 2023.
Cautions and interactions
The gap between enough and too much is small. Chronic excess causes hair and nail loss and nerve problems. Two Brazil nuts can exceed a day's requirement.
Ask a pharmacist before you start anything. Interactions with prescribed medicines are the most common way supplements cause harm, and they are easy to check. Bring the actual packet, or a photo of the ingredients panel, because doses and forms vary enormously between products. Nothing here is a substitute for advice about your own situation.