Placebo consumption over 12 weeks resulted in minimal change in plasma selenium (7.6%) and plasma glutathione peroxidase (-1.2%), confirming that observed increases in the intervention groups were due to selenium intake and not natural variation or time-related factors.

When selenium is consumed, it is absorbed from the gut and used to build a key antioxidant enzyme called glutathione peroxidase. This enzyme needs selenium to work properly, so more selenium means more active enzyme is made. The increased enzyme then breaks down harmful oxidized fats and hydrogen peroxide in the blood, which is why its activity goes up. Without extra selenium, enzyme levels stay flat because the body has no more raw material to make more.