Details of DNA extraction and methylation profiling are described elsewhere.23 Background correction of the raw intensity data and generation of the methylation beta values were done with the R minfi package. Quality-control (QC) steps included the removal of probes with a low (<95%) detection rate at p < 0.01. Array control probes were inspected manually, and low-quality samples (e.g., samples with inadequate hybridization, bisulfite conversion, nucleotide extension, or staining signal) were removed. Samples with a low call rate according to the Illumina-based threshold (samples with <450,000 probes detected at p < 0.01) were removed. LBC samples had been genotyped with the Illumina 610-Quadv1 genotyping platform. Genotype information from the 65 SNP control CpG probes on the methylation chip were cross-validated with those from the genotyping chip with the R wateRmelon package. Where there was low correspondence, samples were excluded (n = 9). We also excluded eight participants whose reported sex did not match their predicted sex according to methylation levels for probes on the X and Y chromosomes.