Effect of different levels of dietary zinc on longevity of BALB/c mice inoculated with plasmacytoma MOPC 104E.

The effect of different levels of Zn intake on survival was studied in 6 groups of 4-week-old BALB/c mice inoculated with MOPC 104E tumor cells. The first 3 groups received either a Zn-deficient (0.5 microgram Zn/g), a Zn-supplemented (1 mg Zn/g), or a control diet (37.5 micrograms Zn/g) starting 11 days after tumor inoculation (T11). The remaining 3 groups received the same diets starting the day the tumor was implanted (T0). The mean survival of rats beginning the Zn-deficient diet at T11 was significantly increased compared with that of the control group. However, when the same diet was begun at T0, the mean survival of the Zn-deficient group was significantly reduced; for this group the results probably related to the combined adverse effects from prolonged Zn deficiency and to those effects of the tumor itself. Similarly, excess Zn intake significantly prolonged the mean survival when given at T11. However, excess Zn intake at T0 produced no significant effect on survival, probably because of the elevation of plasma Zn level following oral Zn intake that occurred before the establishment of the tumor or possibly because of the inability of the small intestine to absorb excess Zn at T11 when the tumor was fully developed.