The protective but nonsynergistic effect of dietary beta-carotene and vitamin E on skin tumorigenesis in Skh mice.

Various epidemiological and experimental studies have indicated that beta-carotene and vitamin E protect against a variety of cancers. This investigation determined whether a synergistic protective effect could be observed against chemically induced skin tumorigenesis in Skh mice by combining these two antioxidants in the diet. Forty-five mice were used in each of four diet groups. Control animals were fed standard mouse chow. Three other groups received the chow supplemented with one of the following: 0.5% beta-carotene, 0.12% vitamin E (added as d-alpha-tocopheryl succinate), or 0.5% beta-carotene + 0.12% vitamin E. Mice were topically treated with a single application of the initiator 7,12-dimethylbenz[a]anthracene and promoted with multiple applications of phorbol 12-myristate 13-acetate. Mice were observed for tumors each week for 27 weeks after initiation. The protective effect of each diet was determined by the decrease in the number of skin tumors in supplemented diet groups compared with that of the control diet group. Decreases in the number of cumulative tumors at Week 27 were 32% for beta-carotene-, 25% for vitamin E-, and 21% for beta-carotene+vitamin E-supplemented diet groups. However, differences in the number of tumors among the three groups supplemented with beta-carotene and/or vitamin E were not statistically significant. Thus, although protection was provided by the individual supplements, there was no synergistic effect for a decrease in the number of chemically induced skin tumors by the simultaneous dietary administration of beta-carotene and vitamin E.