Antioxidant

What Is an Antioxidant?

An antioxidant is any molecule that inhibits the oxidation of other molecules. In biology, oxidation produces free radicals — unstable atoms or molecules with unpaired electrons that can damage cells, proteins, lipids, and DNA in a chain reaction known as oxidative stress. Antioxidants neutralize free radicals by donating an electron without becoming reactive themselves, interrupting the damaging chain.

Free radicals are generated naturally during normal metabolism, immune responses, and exercise, and are increased by smoking, air pollution, ultraviolet radiation, and alcohol consumption.

Types and Food Sources

Antioxidants include vitamins, minerals, and phytochemicals. Key examples include:

• Vitamin C: Found in citrus fruits, bell peppers, kiwi, and broccoli. Water-soluble; protects aqueous compartments of cells.
• Vitamin E: Found in sunflower seeds, almonds, and wheat germ oil. Fat-soluble; protects cell membranes.
• Beta-carotene: Found in carrots, sweet potatoes, and leafy greens. Converted to vitamin A in the body.
• Selenium: Found in Brazil nuts, seafood, and whole grains. A component of glutathione peroxidase enzymes.
• Polyphenols and flavonoids: Found in berries, green tea, dark chocolate (70%+ cocoa), and red wine.

Antioxidants in Context

While observational studies consistently link high intake of antioxidant-rich foods to lower rates of cardiovascular disease and certain cancers, clinical trials of isolated antioxidant supplements have shown mixed or neutral results. High-dose beta-carotene supplements, for example, increased lung cancer risk in smokers in two large trials. This suggests that antioxidants work synergistically within the complex matrix of whole foods rather than as isolated compounds. Food-first approaches remain the evidence-based recommendation.