Why is selenium combined with vitamin C in this supplement — don't they duplicate each other?

Selenium and vitamin C are both antioxidants, but they act through different mechanisms. Selenium is a component of enzymes — in particular, glutathione peroxidases — that neutralise peroxides and help cells cope with oxidative stress. Vitamin C is a water-soluble antioxidant that intercepts free radicals directly in the aqueous environment of the cell and in the intercellular space. So they complement rather than duplicate each other.

Besides its antioxidant role, vitamin C is involved in collagen synthesis, the absorption of certain minerals and the normal functioning of the immune system. This makes it a valuable ingredient in its own right, not just a ‘booster’ for selenium.

From a practical point of view, combining the two ingredients in one tablet makes things simpler: you do not need to find a separate source of vitamin C if your diet is short of it. However, if you are already taking a multivitamin with vitamin C or a separate high-dose ascorbate, it is worth keeping your total daily vitamin C intake within reasonable limits.

If you take several mineral supplements or complexes containing selenium at the same time, it is advisable to consult a specialist so as not to exceed the safe intake level of this trace element.