Positives

• Long COVID patients show measurable depletion of antioxidant defenses (glutathione, selenium, zinc), and observational data link low serum selenium to more severe acute COVID-19 and slower convalescent recovery PMC.
  
  

Negatives

• Selenium has not been tested as a single agent for Long COVID in any randomized trial; the strongest evidence is for the CoQ10+selenium combination, so isolated selenium dosing rests on extrapolation rather than direct data International Journal for Vitamin and Nutrition Research.
  
  

Hurdles & Side Effects

• Selenium has a narrow therapeutic window: chronic intake above 400 µg/day risks selenosis (hair loss, brittle nails, garlic breath, peripheral neuropathy), so the standard recommendation is to target 200 µg/day from supplements plus dietary sources RTHM.