Garlic as an antioxidant: the good, the bad and the ugly.

Garlic has played an important dietary and medicinal role throughout the history of mankind. In some Western countries, the sale of garlic preparations ranks with those of leading prescription drugs. The therapeutic efficacy of garlic encompasses a wide variety of ailments, including cardiovascular, cancer, hepatic and microbial infections to name but a few. However, the elucidation of its mechanism for therapeutic action has proved to be more elusive and a unifying theory, which could account for its reported multifarious activities, is yet to emerge. Reactive oxygen species (ROS) seem to be at the core of many disease processes and it is an attractive and convenient hypothesis that garlic might exert its activities through modulatory effects on ROS. A literature search on garlic and its antioxidant potential churned up a surprisingly large amount of data, some of it good, some bad and some of its definitely ugly. Various preparations of garlic, mainly aged garlic extract (AGE), have been shown to have promising antioxidant potential. However, the presence of more than one compounds in garlic, with apparently opposite biological effects, has added to the complexity of the subject. Raw garlic homogenate has been reported to exert antioxidant potential but higher doses have been shown to be toxic to the heart, liver and kidney. So where do we stand today on this issue of garlic? Is garlic always good for health? How safe is it? Is it necessary to isolate the antioxidant compounds for its medicinal use in a more effective way? These issues are addressed in this review. Copyright 2003 John Wiley & Sons, Ltd.