Preventive potential of antioxidative vitamins and carotenoids on cancer.

Epidemiological and experimental research indicated some time ago that vitamins might act as protective agents in carcinogenesis. However, only more recently prospective studies proved a significant inverse correlation between certain vitamins and cancer at different site. The Basel Study (comprising 3756 healthy adult volunteers) is unique in its immediate measurement of the plasma vitamins at the time of the clinical assessment (1971-1973). The complete mortality follow-up allows testing of several hypotheses regarding the molecular basis of cancerogenesis. Among these mechanisms, aggressive oxygen species have been implicated. By analyzing plasma concentrations of essential antioxidants in cancer cases and survivors, we demonstrated a significantly negative inverse correlation between plasma beta-carotene and all cancer (n = 102, p less than .01), cancer of the lung (n = 37, p less than .01) and stomach (n = 17, p less than .05). Low retinol was related only to gastric cancer (p less than .01); low vitamin C and low vitamin E was related to all cancer and gastric cancer (p less than .05). The estimated antioxidant potential calculated as the molar product of vitamins C, E and beta-carotene showed a highly significant inverse correlation with all cancer and cancer of the lung and the stomach (p less than .01). These data and other newer studies strongly support the antioxidants in a role as natural inhibitors which may act on cancer initiation or promotion. Finally the convergence of results of the many epidemiological and experimental studies allow more soundly based conclusions with regard to dosage and time of vitamin intake in cancer.