Antioxidants are molecules that can neutralize free radicals, which are highly reactive compounds produced by normal metabolism, inflammation, pollution, smoking, UV light and some drugs. Free radicals can damage DNA, proteins and lipids, contributing to aging and diseases such as cancer and cardiovascular disorders. Antioxidants work mainly by donating electrons to free radicals, stabilizing them before they attack cell components.

The body produces its own antioxidant defenses, including enzymes like superoxide dismutase, catalase and glutathione peroxidase, along with small molecules such as glutathione, uric acid and bilirubin. Diet supplies additional antioxidants, notably vitamins C and E, carotenoids, polyphenols and other plant compounds found in fruits, vegetables, nuts, seeds, tea, coffee and cocoa.

Laboratory and animal studies show that antioxidants can limit oxidative damage and influence cell signaling, inflammation and gene expression. However, evidence from large human trials of antioxidant supplements is far less positive. High dose beta carotene increased lung cancer risk in smokers, and some vitamin E trials showed increased overall mortality or higher risk of certain strokes. For many diseases, antioxidant supplements have produced little or no clear benefit.

Current research suggests that context matters. The effects of antioxidants depend on dose, chemical form, health status, and whether they come from whole foods or isolated pills. Antioxidants can also behave as pro oxidants under some conditions. Overall, a balanced diet rich in plant foods appears consistently associated with better health, while routine high dose antioxidant supplementation for prevention of chronic disease is not supported and may sometimes be harmful.