CYP1A2 and Parkinson disease: Conversely, moderate/advanced PD patients compared with HS showed significantly lower levels of basal caffeine (1.13 ± 1.11 vs. 2.13 ± 2.14 μg/ml; U = 721, p = 0.009), significantly higher caffeine absorption (0.79 ± 1.48 vs. 0.11 ± 2.14 μg/ml; U = 1348, p = 0.022), and statistically similar CYP1A2 activity (0.26 ± 24 vs. 0.25 ± 0.20; U = 1007, p = 0.83).