An antioxidant is a chemical that prevents the oxidation of other chemicals. In biological systems, the normal processes of oxidation (plus a minor contribution from ionizing radiation) produce highly reactive free radicals. These can readily react with and damage other molecules: in some cases the body uses this to fight infection. In other cases, the damage may continue to the body's own cells. The presence of extremely easily oxidisable compounds in the system can "mop up" free radicals before they damage other essential molecules.

The following vitamins have shown positive antioxidants effects:

• Ascorbic acid (vitamin C) is a water-soluble compound that fulfills this role, among others, in living systems. Important sources include citrus fruits (like oranges, sweet lime etc.), green peppers, broccoli, green leafy vegetables, strawberries, raw cabbage and tomatoes.