Free radicals may be involved in the aetiology of cancer and cardiovascular diseases. In epidemiological studies poor plasma levels of all essential antioxidants are associated with increased relative risks; in particular, low levels of carotene and vitamin E with the risk of cancer and ischemic heart disease, respectively. The studies suggest that for optimal synergistic protection the plasma antioxidant levels should simultaneously exceed the threshold values of 28-30 μmol/l lipid-standardized vitamin E, 40-50 μmol/l vitamin C, 0.4-0.5 (μmol/l carotene and 2.2-2.8 μmol/l lipid-standardized vitamin A. However the preventive efficacy of an optional antioxidant status is still to be proven in randomized intervention trials. Although these antioxidant micronutrients may be the primary protective components of vegetable-rich ‘preventive' diets, the potentials of other plant components await exploration, eg carotenoids other than β-carotene, bioflavonoids and oxygen-sensitive B-vitamin
