The generation of reactive oxygen species (ROS) is associated with life in 
aerobic conditions. ROS are thought to be implicated in the pathogenesis of 
various human diseases since they are capable of damaging biological 
macromolecules such as DNA, carbohydrates and proteins. The organism maintains 
defense against ROS, including enzymes and low molecular-weight antioxidants. An 
important source of antioxidants is diet which contains numerous compounds 
exhibiting antioxidant activity. A shortage of antioxidants in the diet might 
promote coronary heart disease through accumulation of oxidized LDL in 
macrophages. However, antioxidants may also influence endothelial functions, 
smooth muscle cell proliferation, thrombosis and plaque rupture. Consumption of 
fruits and vegetables, olive oil, red wine and tea is inversely correlated with 
heart disease rates. These foods are particularly rich in natural antioxidant 
nutrients, including ascorbate (vitamin C), the tocopherols (vitamin E) and 
carotenoids. More than 600 naturally occurring carotenoids have been identified. 
These compounds are plant pigments that provide the bright color of various 
fruits and vegetables; lycopene, which gives tomatoes their red color, is under 
active research. Flavonoids are > 4,000 naturally occurring substances which 
provide color, texture and taste for plant foods. As free radical scavengers, 
flavonoids inhibit lipid peroxidation, promote vascular relaxation and help 
prevent atherosclerosis. A sufficient supply with antioxidants from diet might 
help prevent or delay the occurrence of pathological changes associated with 
oxidative stress. When diet fails to meet the antioxidant requirement, dietary 
supplements might be indicated. The recently coined term nutriceuticals 
describes a variety of nonprescription products that are used to enhance health. 
The best known are vitamin E, vitamin C, carotenoids, coenzyme Q10, flavonoids 
and the amino acid L-arginine. Rigorous clinical trials, particularly among 
high-risk groups, are needed before they can be recommended routinely to 
patients.