Abstract Cardiovascular disease (CVD), including coronary heart disease (CHD) and stroke, is the leading cause of mortality and morbidity in both men and women in the US. Well-established risk factors for CVD include modifiable lifestyle and non-modifiable host/biological variables, such as smoking, diet, BMI, age, sex, and race/ethnicity, as well as quantitative cardiovascular traits, such as total cholesterol, triglyceride, high- density/low-density lipoprotein cholesterol, blood pressure, and fasting glucose. However, it is not yet clear through which molecular mechanisms these lifestyle/host risk factors influence the cardiovascular traits and CVD risk. Large-scale multiplatform omics data, including whole-genome sequencing, DNA methylation, and gene expression data, have been recently generated in tens of thousands of well-phenotyped individuals in the NHLBI Trans-Omics for Precision Medicine (TOPMed) program. These large-scale multi-omics and phenotype data resources provide an unprecedented opportunity to investigate the relationships among environmental/lifestyle risk factors and cardiovascular traits, and how molecular phenotypes work as intermediate factors between them. However, it remains a significant analytical challenge to delineate those complex relationships in the presence of multiple types of high-dimensional omics data. The objective of this research is to capitalize on the multi-omics and phenotype data in the TOPMed program and our recently developed statistical methods for high-dimensional mediation analysis to quantify the extent to which DNA methylation and gene expression mediate the effects of environmental/lifestyle risk factors on (Aim 1) quantitative cardiovascular traits and (Aim 2) the risk of incident CVD. We will identify mediating markers based on high-dimensional variable selection methods and estimate the total mediation effects of DNA methylation and gene expression, each alone and jointly, using 6,000 individuals in the Framingham Heart Study (FHS) study as the discovery cohort and over 2,000 and 1,000 individuals, respectively, in the Women’s Health Initiative (WHI) and Multi-Ethnic Study of Atherosclerosis (MESA) as validation cohorts. This study will provide deep insights into molecular phenotypes and biological pathways that mediate the effect of lifestyle/host risk factors on cardiovascular traits and CVD risk. Our findings may contribute to the discovery of novel biomarkers and therapeutic targets for CVD, and biomarker-based precision prevention for this devastating disease. The multi-omics-based mediation analysis pipeline established and refined through this proposed research will also be applicable to other heart, lung and blood diseases in the TOPMed program.