Calorie Restriction Reduces the Incidence of Myeloid Leukemia Induced by a Single Whole-body Radiation in C3H/He Mice

Dietary restriction, especially caloric restriction, is a major modifier in experimental carcinogenesis and is known to decrease significantly the incidence of neoplasms. Gross and Dreyfuss [Gross, L. & Dreyfuss, Y. (1984) Proc. Natl. Acad. Sci. USA 81, 7596-7598; Gross, L. & Dreyfuss, Y. (1986) Proc. Natl. Acad. Sci. USA 83, 7928-7931] reported that a 36% restriction in caloric intake dramatically decreased the radiation-induced solid tumors and/or leukemias. Their protocol predominantly produced lymphatic neoplasms. It is of interest to observe the effect of caloric restriction on radiation-induced myeloid leukemia, because the disease was observed to have been increased in the survivors of the atomic bombs in Hiroshima and Nagasaki. The spontaneous incidence of myeloid leukemia in C3H/He male mice is 1%, and the incidence increased to 23.3% when 3 Gy of whole-body x-ray irradiation was given. However, the incidence of myeloid leukemia was found to be significantly decreased by caloric restriction; it was reduced to 7.9% and 10.7% when restriction was started before (6 weeks old) and after (10 weeks old) irradiation, respectively. In addition, the onset of the myeloid leukemia in both restricted groups was prolonged to a greater extent as compared with the control diet group. Caloric restriction demonstrated a significant prolongation of the life span in the groups on a restricted diet after having been exposed to irradiation, either before or after dietary restriction, in comparison with mice that were only irradiated.