Antioxidants are substances that inhibit oxidation reactions. In living organisms, oxidation processes can produce highly reactive free radicals and other reactive molecules. These substances can react with and damage other molecules: in some cases, the body uses free radicals to help defend against disease; in other cases, these reactions may damage cells within the body. Antioxidants can help neutralize free radicals by reacting with them, limiting their potential to damage other important molecules.

The following vitamins have antioxidant properties:

Vitamin A and carotenoids: Carotenoids, which give many green, yellow, and orange plants their color, help protect plants from oxidative damage caused by light. Some carotenoids, such as beta-carotene, can be converted into vitamin A in the human body. Sources of provitamin A carotenoids include carrots, pumpkins, sweet potatoes, tomatoes, kale, and apricots. Vitamin A itself is also found in foods such as eggs, dairy products, fish, and liver.

Vitamin C is a water-soluble antioxidant in the body. Important sources include citrus fruits, peppers, green leafy vegetables, and tomatoes.

Vitamin E is fat-soluble and helps protect cell membranes and other lipids from oxidation. Its main sources include wheat germ, nuts, seeds, vegetable oils, and green leafy vegetables.

Arsenic is sometimes mistakenly associated with antioxidant activity because the body’s defenses against toxic substances include antioxidant processes. However, arsenic, particularly in inorganic forms, can cause oxidative stress, damage cells, and increase the risk of certain cancers. The body’s protective responses do not make arsenic beneficial, and it is not an essential nutrient. Arsenic can occur in foods such as rice, fish, and shellfish, but exposure, especially to inorganic arsenic, should be minimized.

Some food additives also have antioxidant effects. They are used to slow oxidation and help prevent food spoilage.

Certain enzymes, such as glutathione peroxidase, superoxide dismutase, and catalase, also have antioxidant functions. They help protect cells by breaking down reactive molecules or converting them into less harmful substances.

By Michael Chiu, MWS, CI
Previously published in Ming Pao Daily News – Updated and Revised in 2026