Antioxidants

Antioxidants are molecules that inhibit oxidation, a chemical reaction that can produce free radicals leading to cell damage. In biological systems, antioxidants neutralize reactive oxygen species and reactive nitrogen species, limiting lipid peroxidation, DNA damage, and protein modification. They act directly as scavengers or indirectly by supporting cellular defense systems. Oxidative stress results when production of reactive species exceeds the capacity of antioxidant defenses and has been associated with aging and several diseases, though causation is complex.

Endogenous antioxidants include enzymatic systems such as superoxide dismutase, catalase, and glutathione peroxidase, which convert reactive species into less reactive molecules. Non-enzymatic endogenous antioxidants include glutathione, uric acid, bilirubin, and coenzyme Q10, among others.

Exogenous antioxidants are obtained from the diet. Notable examples are vitamins C and E, carotenoids such as beta-carotene, lycopene, and lutein, and various polyphenols. Selenium and other trace minerals serve as cofactors for antioxidant enzymes. In plants and foods, antioxidants also help protect against oxidative damage during storage and processing.

Dietary patterns rich in fruits, vegetables, whole grains, and nuts tend to be high in antioxidants. Epidemiological studies link such patterns with reduced risk of some chronic diseases, but randomized trials of isolated antioxidant supplements have yielded mixed or null results and in some cases have suggested possible harm at high doses. Current guidance generally emphasizes a diet-based approach rather than high-dose supplementation, except in specific deficiency states.