VDR and chronic obstructive pulmonary disease: First, the high levels of parathyroid hormone as observed in patients with COPD (Jackson et al. 2013) may enhance the risk of sarcopenia (Visser et al. 2003) and accentuate an age-related reduction in VDR expression (Bischoff-Ferrari et al. 2004a) and muscle strength (Bischoff-Ferrari et al. 2004b).