LEVELS OF ANTIOXIDANT INTAKE FROM FOOD SOURCES
In the absence of conclusive evidence linking antioxidant intake with a reduced risk of CHD, dietary recommendations are difficult. Vitamin C and B-carotene are available from fruits and vegetables, and vitamin E from vegetable oils. Results from southem European countries consuming the classical Mediterranean diet show that high plasma levels of these antioxidants can be achieved. This diet is characterized by a preference for fresh products and frequent consumption of fruits, vegetables, legumes, and oils with a high vitamin E content. In contrast, major parts of populations in the United States or in northem parts of Europe do not consume optimal amounts of antioxidant nutrients. The availability of lower-priced convenience foods in the United States acts against the consumption of freshly prepared foods. Thus, only 40% of Americans con-sume five servings of fruit and vegetables daily, as recommended by the US national food guide, the Food Guide Pyramid. Only a quarter consumed fruits or vegetables rich in vitamin C or the carotenoids, and on any given day 54% ate no fruit at all.
A recent reanalysis of the Second National Health and Nutrition Examination Survey (NHANES II) data showed that vitamin supplements are the major contributors of the principal antioxidant micronutrients in the US diet (28% of vitamin C and 46% of vitamin E). Estimates of the requirement for micro nutrients are based on the minimum quantity necessary to prevent a deficiency. The translation of minimum requirement to a dietary recommendation for population groups necessitates that allowance be made for a number of variables, including periods of low intake, increased utilization, individual variability, and bioavailability.
In the United States, the Recommended Daily Allowances (RDAs) incorporate "margins of safety" intended to be sufficiently generous to encompass the variability in the minimum requirement among people, and bioavailability from different food sources. To date, recommendations on micronutrient intake have therefore been primarily intended to prevent clinically overt deficiencies such as scurvy. If, however, observational and experimental evidence continues to show that the prevention of slow multistage processes such as CVD and cancer might require a higher intake of some essential antioxidants, then a recommended intake should be devised referring to amounts considered sufficient for the avoidance of these disease states.
Gey suggests that the present recommendations will require either an upgrading or an additional term, e.g., a recommended optimum intake (ROl) that will vary with gender and age, with special requirements for smokers, pregnancy, and the elderly. The ROI could be defined as sufficient (culture-and/or regionspecific) intake to achieve blood levels associated with the observed minimum relative risk of disease. For example, Carr and Frei have suggested a doubling of the current RDA for vitamin C for optimum reduction in chronic disease risk. A ROI would simply quantify specific dietary constituents of conceivably crucial importance within the still desirable "five servings of fruit and vegetables daily."
