Figure 2.

Hours per week of recent indoor secondhand tobacco smoke (SHS) exposure and cg05575921 methylation in nonsmokers. (A) Scatterplot of cg05575921 methylation in CD14+ monocyte samples (y-axis: converted to beta-values) versus hours per week of recent indoor SHS exposure (x-axis). (B) Boxplot of cg05575921 methylation (y-axis, beta-value) by categories of recent SHS exposure per week (none: 0 hours, low–moderate: 1–9 hours, heavy: ≥10 hours), in all nonsmokers (overall), and stratified by smoking status (never-smokers and former smokers having quit for at least 15 years). Covariates included age, sex, race/ethnicity, education level, smoking status, pack-years, time since quitting smoking (former smokers only), site of data collection, and estimates of residual sample contamination with non-monocyte cell types; significance indicated as follows: **p < .01; *.01 ≤ p < .05.