A Randomized Study on the Effect of Vitamin D₃Supplementation on Skeletal Muscle Morphology and Vitamin D Receptor Concentration in Older Women

Vitamin D₃ supplementation increased intramyonuclear VDR concentration by 30% and increased muscle fiber size by 10% in older, mobility-limited, vitamin D-insufficient women. Further work is needed to determine whether the observed effect of vitamin D on fiber size is mediated by the VDR and to identify which signaling pathways are involved.