Antioxidant

Antioxidant, is any of a group of chemical compounds that may prevent certain types of cell damage. Antioxidants block the effects of oxidation, a chemical reaction in which a substance loses electrons, often while combining with oxygen. Antioxidants are important because they protect cells from the effects of free radicals, unstable molecules produced by oxidation. Scientists believe free radicals may be involved in the aging process as well as in a number of diseases.

In the human body, cells create free radicals when oxygen combines with food molecules to produce energy. Radiation, cigarette smoke, and air pollution also trigger the production of free radicals. Free radicals can attract and "steal" electrons from almost any nearby molecule to replace the electrons they lost during oxidation. Such attacks can damage the cell and can cause changes in genes. Antioxidants are the body's defense against free radicals. An antioxidant can provide an electron to a free radical before the free radical attacks important cell structures.

The body naturally produces certain enzymes that are antioxidants. In addition, vitamins C and E and certain plant chemicals, such as carotenoids and flavonoids (often called bioflavonoids), are antioxidants.

Fruits and vegetables are rich sources of dietary antioxidants. Citrus fruits are a rich source of vitamin C. Vitamin E is found in vegetable oils and nuts. Foods plentiful in beta-carotene or other carotenoids tend to be deep yellow or green, such as carrots and spinach. Flavonoids occur in many fruits and vegetables. Some studies have connected a diet rich in antioxidants with a reduced risk of cancer, heart disease, cataracts, and other diseases common among older people. Scientists are trying to determine if these reduced risks are due to the antioxidants or to some other factor.

Vitamin A

Vitamin A, also known as retinol, occurs naturally only in animals. Eggs, liver, and milk provide much vitamin A. Some plants contain substances called carotenes, or provitamins A, which the body converts into vitamin A. These plants include cantaloupes, carrots, sweet potatoes, dark green leafy vegetables, and deep yellow vegetables.

Vitamin A is essential for the development of babies before birth and the growth of children. It is especially needed for the growth of bones and teeth. Vitamin A keeps the skin healthy and helps produce mucous secretions that build resistance to infection. People who do not get enough vitamin A may develop xerophthalmia, in which the surface of the eye becomes dry and likely to develop infection. Vitamin A also forms part of the two pigments that help the eyes to function normally in light that varies in intensity. Night blindness is an early symptom of a deficiency of vitamin A.