[Effect of calcium and vitamin D on skeletal muscle]

Patients with vitamin D insufficiency often exhibit muscle weakness and/or atrophy which can be cured by vitamin D and Ca supplementation. However, its molecular mechanism is largely unknown. The direct effects of vitamin D on skeletal muscle cells include induction of transcription factors such as c-myc (genomic action) ;and activation of Ca channels, Src tyrosine kinase and MAP kinase (non-genomic action). Recent studies on VDR gene knockout mice revealed that VDR also regulates expression of the MyoD family of transcription factors in skeletal muscle. Thus, vitamin D and Ca appear to regulate proliferation, maturation and function of skeletal muscle through these complex actions.