VDR and Parkinson disease: The presence of VDR and 1-alpha-hydroxylase, the enzyme that converts 25(OH)D to its active form 1,25-dihydroxyvitamin D (1,25(OH)D), in substantia nigra underlines the role of vitamin D in PD suggesting that vitamin D hydroxylation and activation is also completed in central nervous system (CNS), and therefore the deficit of vitamin D concentration causes dopaminergic neurons death [62,66].