Circulatory 25(OH)D and 1,25(OH)2D as differential biomarkers between multiple system atrophy and Parkinson's disease patients

•Low serum 1,25(OH)2D and 25(OH)D concentrations in MSA, whereas only low 25(OH)D in PD.•The decrement of serum 1,25(OH)2D concentration is higher in MSA than in PD.•In MSA, 25(OH)D correlate with 1,25(OH)2D, UMSARS and H&Y.•In PD, 25(OH)D correlate with 1,25(OH)2D and H&Y.•25(OH)D and H&Y display the highest diagnostic performance as binary classifier for PD and MSA.