Fig. 1.

Association of AAO and tobacco use, smoking intensity and smoking duration in iPD. a Scatter plot of AAO of patients with iPD stratified by smoking status. Median values and interquartile ranges (IQR) are depicted. b Correlation between number of cigarettes smoked per day and AAO of patients with iPD. c Correlation between number of years of smoking until AAO and AAO of patients with iPD. p value: exploratory Mann–Whitney U test was performed for pairwise comparisons; non-parametric Spearman’s correlation and simple linear regression analyses were used to assess interactions between variables; p = Spearman’s exploratory p value, r = Spearman’s rank correlation coefficient