One of the most popular theories on aging is the "free radical theory." This theory attributes aging and age-associated diseases to the damage caused by free radicals. Free radicals are highly reactive, toxic forms of oxygen molecules that bind to and destroy cellular components. Compounds that prevent this type of damage are known as "antioxidants."

Antioxidants found in food include vitamins A, C, and E. Beta carotene is a precursor of vitamin A. The minerals selenium and zinc are required for the activity of antioxidant enzymes in the body. Fresh fruits and vegetables are both good sources of antioxidants.In addition, ginkgo may be used to prevent dementia in people with a family history of Alzheimer's disease.