Antioxidant

Antioxidants are compounds that inhibit oxidation, protecting cells from damage caused by free radicals and reactive oxygen species. They can donate electrons or hydrogen atoms to stabilize reactive species, terminating chain reactions. The term encompasses endogenous defenses and dietary compounds.

Endogenous antioxidants include enzymatic systems such as superoxide dismutase, catalase, and glutathione peroxidase, and non-enzymatic molecules like glutathione, ubiquinone, uric acid, and melatonin. Exogenous antioxidants are obtained from foods and supplements, notably vitamins C and E, carotenoids (beta-carotene, lycopene), and polyphenols (flavonoids, resveratrol). Dietary sources include fruits, vegetables, nuts, seeds, tea, coffee, and vegetable oils.

In food science, antioxidants such as tocopherols, BHT, and BHA are used to prevent rancidity and extend shelf life. In health contexts, epidemiological studies associate higher antioxidant intake with lower risk of several diseases, but randomized trials of supplements have produced mixed results, with some showing no benefit and others suggesting possible harm at high doses. Therefore, a diet rich in diverse plant foods is generally recommended rather than high-dose antioxidant supplements.

Mechanistically, antioxidants can scavenge free radicals, chelate metal ions, or repair oxidized molecules. They play roles in cellular signaling and immune function, but redox balance is complex; excessive antioxidant supplementation can disrupt physiological processes.