Sex, age at first (i.e., baseline) and last interview were included as covariates. Two additional covariates were also included. First, three principal components, reflecting continuous variation in genetic ancestry were derived from all the GWAS data (details in Supplemental Materials) and included to account for subtle ancestral differences40. Second, the type of genotyping array used for each individual was included as a covariate in order to control for potential differences in genomic content, quality control or imputation (Table S1 for descriptive data).
