VDR and vitamin D deficiency: Conversely, elderly individuals face an elevated risk of pathologies stemming from vitamin D deficiency due to factors like diminished skin synthesis of vitamin D (owing to less sun exposure) and metabolic changes, including reduced kidney formation of 1α,25-dihydroxy-vitamin D, or decreased intestinal calcium absorption due to a decline in vitamin D receptor (VDR) intestinal expression (Gallagher 2013).