Retinoids or Carotenoids: Is There Another Choice?

Both retinoids and carotenoids decrease cancer occurrence in selected animal models of carcinogenesis, but the retinoids appear to have more potent activity against a wider variety of tumors. Future use of retinoids for cancer prevention will be limited, however, because of their toxic effects on bone and skin (among other organs). In contrast to retinoids, carotenoids seem to be free of important toxicity and this fact makes them more promising for use in the general adult population. However, the idea that carotenoids have a cancer-preventive effect in humans is based almost entirely on epidemiological studies of diet and serum which could simply reflect the effects of some other dietary constituents. In the search to explain the profoundly lower risk of death associated with eating a diet high in fruits, vegetables, and grains, there is a place for clinical trials testing one specific nutrient, such as β-carotene, against one disease, such as lung cancer, but we should not rely exclusively on these narrowly focused studies. In addition, careful analyses of cohort studies may reveal broad patterns of diet that are associated with lower mortality. These diets can then be tested in clinical trials for their efficacy against a variety of causes of death and disability. For now, the most rational and prudent choice would be to consume a diet high in fruits, vegetables, and grains and not to take either supplemental antioxidants or retinoids until there is clear evidence of their effectiveness and safety.