Antioxidant defense systems: the role of carotenoids, tocopherols, and thiols

Free radicals (unstable atoms with unpaired electrons) are by-products of certain biochemical reactions occurring within the body's cells. These free radicals are highly reactive (reactive oxygen species) and can damage DNA, proteins and cell membranes. Antioxidants such as carotenoids (including vitamin A precursors), tocopherols (vitamin E) and thiols (compounds containing sulfur) protect tissues from damage by inactivating reactive oxygen species. The ability of antioxidants to act as scavengers (inactivators) of free radicals may be important in explaining the possible anti-cancer properties of beta-carotene, a form of vitamin A and a carotenoid. Tocopherols are fat-soluble antioxidants that provide the greatest protection for cell membranes from destruction by oxygen radicals. The concentration of vitamin E in a cell membrane determines the susceptibility of the membrane to damage by free radicals. Glutathione is the most important cellular thiol for scavenging free radicals. Carotenoids, tocopherols and thiols are the natural defense mechanisms of the cell, protecting it from the damaging effects of free radicals. (Consumer Summary produced by Reliance Medical Information, Inc.)