Simvastatin or HFD ameliorates radiation‐associated hematopoietic syndrome of male or female mice. A,B) Volume of dissected thymuses A) and Photographs of spleens B) from male mice in the four groups, the thymuses and spleens were obtained at day 21 after 4 Gy TBI. Mean ± SD. Significant differences are indicated: *P < 0.05, ***P < 0.005 by Student's t‐test between each two cohort, n = 18 per group. C,D) Volume of dissected thymuses C) and photographs of spleens D) from female mice in the four groups, the thymuses and spleens were obtained at day 21 after 4 Gy TBI. Mean ± SD. Significant differences are indicated: *P < 0.05, ***P < 0.005 by Student's t‐test between each two cohort, n = 18 per group. E,F) The levels of IL‐6 in PB of male E) and female F) were examined. Significant differences are indicated: *P < 0.05, **P < 0.01 by Student's t‐test between each two cohort, n = 18 per group. G,H) The levels of MDA in PB of male G) and female H) were examined. Significant differences are indicated: *P < 0.05, **P < 0.01, ***P < 0.005 by Student's t‐test between each two cohort, n = 18 per group.