Anti-sarcopenic effects of active vitamin D through modulation of anabolic and catabolic signaling pathways in human skeletal muscle: A randomized controlled trial

Background: The muscle-building and strengthening effects of the active form of vitamin D in humans remain unclear. Methods: In this ancillary study of the Diabetes Prevention with active Vitamin D trial, we examined clinical and experimental aspects to investigate the effects and mechanisms of eldecalcitol, an active form of vitamin D, in preventing sarcopenia. We examined changes in molecules involved in muscle synthesis and degradation pathways in muscle samples from 32 participants before and after 1 year of eldecalcitol or placebo treatment. The protein levels of molecules involved in muscle synthesis and degradation pathways were examined using western blotting. Additionally, the skeletal muscle and body fat volumes were measured using bioelectrical impedance analysis with a body composition analyzer. Results: We found that eldecalcitol treatment for 1 year resulted in higher phosphorylation levels of mTOR and FOXO1 signaling pathways, which are associated with increased muscle mass and strength than those with placebo treatment. Body composition measurements at 1 year showed that the eldecalcitol group had significantly higher skeletal muscle mass (1.9 % vs. -3.4 %, p = 3.26E-9) and muscle strength (4.1 % vs. -0.7 %, p = 2.57E-17), and lower fat mass (-3.2 % vs. 1.8 %, p = 1.73E-12) than those in the placebo group. Conclusion: This study suggested that the active form of vitamin D regulates the protein synthesis and degradation pathways in human skeletal muscle and may help prevent sarcopenia. This study was registered at UMIN clinical trials registry, UMIN 000005394.