Effects of excess vitamin A and canthaxanthin on salivary gland tumors

The effects of feeding semipurified diets supplemented with excess retinyl palmitate (20,000 and 100,000 IU/kg), beta-carotene (250 mg/kg), and canthaxanthin (250 mg/kg) on 7,12-dimethylbenz[a]anthracene (DMBA)-induced salivary gland tumors were studied in rats. None of the dietary supplements had a significant effect on tumor incidence. Tumor weights, however, tended to be lower in rats fed the dietary supplements compared with the controls. The incidence of tumor-bearing rats with large tumors was significantly lower in rats fed canthaxanthin than in the control rats. At termination of the experiment, the levels of vitamin A were higher in plasma, liver, normal salivary glands, and the tumor of rats fed diets supplemented with the higher level of retinyl palmitate. Feeding the canthaxanthin-supplemented diet had the opposite effect on tissue and plasma vitamin A levels. beta-Carotene supplementation was associated with higher vitamin A concentrations in the liver but not in plasma, salivary glands, or the tumor. The levels of beta-carotene were increased in tissues and plasma of rats fed the beta-carotene-supplemented diet. The results suggest that in this experimental model, the diet-induced modification of tissue or plasma vitamin A levels did not have an effect on tumor incidence.