Fig. 1

Flowchart for this study. The red cross sign means genetic variables not associated with confounding factors and outcomes. Assumption 1 indicates that SNPs are strongly associated with circulating phytosterols levels; Assumption 2 indicates that SNPs are not associated with confounding factors; Assumption 3 indicates that SNPs affect the risk of outcomes via circulating phytosterols levels directly. AD, Alzheimer’s disease; PD, Parkinson’s disease; PD AAO, Parkinson’s disease age at onset; SNP, single nucleotide polymorphism; LD, linkage disequilibrium; IPDGC, International Parkinson Disease Genomics Consortium; TG, triglycerides; HDL-C, high-density lipoprotein cholesterol; UVMR, univariable Mendelian randomization; MVMR, multivariable Mendelian randomization; UKB, UK Biobank; IGAP, International Genomics of Alzheimer’s Project; N, number