Vitamins and cancer chemoprevention.

Chemoprevention is in an area of cancer research with perhaps the greatest potential for reducing cancer mortality. Several agents, and in particular antioxidant vitamins, appear to be effective against early rather than later steps of the premalignant process at different sites. Particular attention must be paid to possible side effects and safety of the agents and to optimal doses in long-term administration regimens. The results of numerous trials on the preventive role of vitamins (e.g. beta-carotene, retinols, retinoids, alpha-tocopherol, ascorbic acid, folic acid) are contradictory and far from conclusive. Multiple primary and secondary intervention trials currently under way should assess in the coming years the role of some vitamins in the prevention of various cancers (oral cavity, pharynx, oesophagus, colon, lung, breast, skin, cervix, bladder).