Aging, exercise, and phytochemicals: promises and pitfalls.

Phytochemicals are emerging comprehensive and versatile sources of antioxidants to be consumed to enhance the body's defenses against harmful reactive oxygen species generated endogenously or exogenously. Tocols, favonoids, and phenolic acids compose the majority of this class of antioxidants, although more complex compounds may also be involved, such as ginsenosides. In vitro and in vivo studies have demonstrated convincingly that dietary supplementation of phytochemicals has beneficial effects against certain types of pathogenesis, disease, cancer, and aging. There is evidence that these effects are related to the ability of phytochemicals to promote the antioxidant defense system and reduce oxidative stress and damage in the cell. However, due to their structural and chemical diversity and complexity, many of the benefits as well as potential adverse effects remain to be examined.