Dietary antioxidants and cancer

Scientifically valid data on the relationship of antioxidants to cancer come from three major sources: human epidemiological studies, experimental studies with animals and in vitro tests for genetic toxicity. Controversies are inevitable when data are either not clear-cut or incomplete. This is clearly the case for the effects of vitamins A, C, E, synthetic antioxidants and selenium on the risk of cancer. Interpretations therefore depend on the criteria selected for evaluation and are influenced by individual or collective judgment. Considerable research indicates the cancer inhibitory effects of vitamin A, vitamin C, synthetic antioxidants and selenium may be due in part to their ability to alter the enzymes involved in the metabolism of carcinogens or to inhibit cancer promotion, rather than their antioxidant properties per se. Vitamin C and E are generally less active inhibitors of overall carcinogenesis, yet their action may relate to the sequestering of genotoxic free radicals. The overwhelming evidence suggests that what we eat can influence the probability of certain types of cancer. It is not at present possible to specify a diet that protects all people. Characterizing and optimizing defense systems may represent an important strategy for minimizing cancer risk. It must be emphasized that any nutrient taken in excess can be toxic. Therefore, the indiscriminate use of supplements may lead to as many complications as what they are aimed at preventing. Therefore, even with the vast accumulation of new knowledge regarding these dietary constituents, nutrition experts continue to emphasize that it is best to eat a varied and balanced diet and maintain weight within a reasonable range.