From experimental studies it is known that free radicals may induce numerous pathological processes, and it has been suggested that, because of their antioxidant capacity, nutrients such as beta-carotene, vitamin C, vitamin E, selenium and zinc may prevent such harmful effects. Epidemiological data from cross-sectional, case-control, and prospective studies have indeed shown a strong relationship between the intake of antioxidant vitamins and minerals, or foods rich in these nutrients, and the risk of cancer and ischaemic cardiovascular diseases (CVD). However, randomised placebo-controlled primary prevention trials, in which antioxidant micronutrients alone or in pairs were given at high doses over long periods, have not been able to prove this potential beneficial effect, and two of these even suggested harmful effects. The seemingly contradictory results between the observational studies and these randomised trials can be explained by the fact that the doses used in clinical trials were much higher than the highest levels reachable by usual dietary intake which have been found to be associated in observational studies with the lowest risk of cancer and CVD. In fact, the only trial which did observe a beneficial effect on total mortality and cancer incidence used nutritional doses of a combination of several vitamins and minerals and was performed on Chinese population with very low baseline micronutrient status, due to poor life conditions in this region (9).