MYOD1 and sarcopenia: In summary, the results of this study indicate that deficiency of active vitamin D down-regulates Sirt1 and Myod1 through reduced VDR-mediated gene transcription, increases p53 and p65 acetylation levels, inhibits the proliferation and differentiation of skeletal muscle precursor cells and skeletal muscle cell regeneration, and increases skeletal muscle cell senescence and SASP, thereby accelerating the occurrence of sarcopenia, while the overexpression of Sirt1 in MSCs can prevent the occurrence of sarcopenia caused by active vitamin D deficiency.