Which of the following vitamins does NOT act as an antioxidant?

Vitamin K is recognized primarily for its vital role in blood coagulation and bone metabolism, rather than its antioxidant properties. While some vitamins, like Vitamins A, C, and E, are well-known for their ability to neutralize free radicals and protect cells from oxidative stress, Vitamin K does not possess this function. Instead, its main contributions to health are related to its enzymatic roles in synthesizing proteins for blood clotting and certain proteins that manage calcium levels in the bones and blood.

Vitamins A, C, and E operate as antioxidants in various ways. Vitamin A, particularly in its active form, retinol, helps to protect lipid membranes from oxidative damage. Vitamin C, as a water-soluble antioxidant, is effective in scavenging free radicals in the aqueous environments of the body. Vitamin E, a fat-soluble antioxidant, protects cell membranes from oxidative damage by quenching lipid peroxyl radicals.

This distinction highlights why Vitamin K is not classified alongside the other vitamins in the context of antioxidant activity. Its contributions to health are essential, but they lie predominantly outside the realm of oxidative stress prevention.