The level of 25-HC is also reduced in plasma of AD/PD patients (1.26 ± 0.28 ng/mL, P < 0.05), as it is in patients diagnosed with PBI (1.28 ± 0.21 ng/mL, P < 0.05), compared to CP (1.54 ± 0.42 ng/mL). Here, CP is linked to Parkinson disease.