Effect of dietary zinc intake on N-methyl-N-nitrosourea-induced mammary tumorigenesis in rats

Numerous studies have shown that zinc nutrition influences the growth of several types of tumor. However, the influence of zinc nutrition on mammary tumorigenesis is not known. To study the effects of dietary zinc intake on N-methyl-N-nitrosourea (MNU)-induced mammary tumorigenesis, female Sprague-Dawley rats were fed an egg-white-based diet providing 3 (Z3), 12 (Z12), or 31 (Z31) mg zinc/kg diet ad libitum. In addition, two pair-fed controls, PFZ12 and PFZ31, were also included. Fourteen weeks after MNU injection, cumulative tumor incidence and total number of tumors were lower in Z3 rats than in Z12 and Z31 rats. Cumulative tumor incidence and total number of tumors were lower in Z3 rats than in PFZ12 rats, but were the same as in PFZ31 rats. Cumulative tumor incidence and total number of tumors were also lower in pair-fed controls than in their corresponding ad libitum controls, but were the same between the ad libitum controls. Overall, the results showed that the effect of marginal zinc deficiency on MNU-induced mammary tumorigenesis in rats was primarily the result of a reduced feed intake associated with marginal zinc deficiency rather than zinc per se.