Phytochemicals as Antioxidants

Overproduction of oxidants (reactive oxygen species and reactive nitrogen species) in the human body is responsible for the pathogenesis of some diseases. The scavenging of these oxidants is thought to be an effective measure to depress the level of oxidative stress of organisms. Antioxidant phytochemicals can be found in many foods and medicinal plants and play an important role in the prevention and treatment of chronic diseases caused by oxidative stress. Phytochemicals are the chemicals extracted from plants. These chemicals are classified as primary or secondary constituents, depending on their role in plant metabolism. Antioxidants are secondary constituents or metabolites found naturally in the body and in plants such as fruits and vegetables. An antioxidant can be defined in simple terms as anything that inhibits or prevents oxidation of a susceptible substrate. Generation of free radicals or reactive oxygen species (ROS) during metabolism and other activities beyond the antioxidant capacity of a biological system gives rise to oxidative stress. Oxidative stress plays a role in heart diseases, malaria, neurodegenerative diseases, AIDS, cancer and in the aging process. Antioxidants may be preventive antioxidants and chain breaking antioxidants. Preventive antioxidants inhibit oxidation by reducing the rate of chain initiation. Natural antioxidants are found to have higher antioxidant activity when compared with that of the synthetic ones. The most publicized phytochemicals with antioxidant properties have been vitamin C, vitamin E and beta-carotene. In view of the laboratory based and clinical findings, the most prudent and scientifically supportable recommendation for the general population is to consume a balanced diet with emphasis on antioxidant-rich fruits and vegetables and whole grains as well as some medicinal plants more frequently because they contain many antioxidant phytochemicals. In the future, more antioxidant phytochemicals in foods and medicinal plants should be separated and identified, and their bioactivities and the mechanism of action should be studied further.