Which mineral acts as an antioxidant and is a component of many enzymes?

• A. Zinc
• B. Copper
• C. Iron
• D. Selenium

Answer: (D)

Selenium’s role as an antioxidant and as a component of many enzymes comes from its incorporation into selenoproteins. In these proteins, the amino acid selenocysteine is built into the active sites, enabling redox reactions that protect cells from oxidative damage. The best-known example is glutathione peroxidase, which neutralizes hydrogen peroxide and lipid peroxides, helping safeguard cell membranes. Other selenoproteins also support antioxidant defenses and are important for thyroid hormone metabolism and normal cellular function, contributing to the activity of many enzymes involved in DNA synthesis and repair.

While zinc and copper are essential cofactors for various enzymes and do participate in some antioxidant systems (for example, copper-zinc superoxide dismutase), selenium’s distinctive advantage is its broad presence in selenoproteins that directly carry out antioxidant reactions. Iron is crucial for oxygen transport and energy production but does not act as an antioxidant; it can promote oxidative stress if not properly regulated.