Objective: The identification of new causal risk factors has the potential to improve cardiovascular disease (CVD) risk prediction and the development of new treatments to reduce CVD deaths. In the general population, we sought to determine whether cortisol is a causal risk factor for CVD and coronary heart disease (CHD). Design and methods: Three approaches were adopted to investigate the association b etween cortisol and CVD/CHD. First, we used multivariable regression in two prospective nest ed case-control studies (total 798 participants, 313 incident CVD/CHD with complete data). Second, a random-effects meta-analysis of these data and previously published prospective associations was performed (total 6680 controls, 69 6 incident CVD/CHD). Finally, one- and two-sample Mendelian randomization analyses were performed (122,737 CHD ca ses, 547,261 controls for two-sample analyses). Results: In the two prospective nested case-control studies, logistic r egression adjusting for sex, age, BMI, smoking and time of sampling, demonstrated a positive association between m orning plasma cortisol and incident CVD (OR: 1.28 per 1 SD higher cortisol, 95% CI: 1.06-1.54). In the meta-analy sis of prospective studies, the equivalent result was OR: 1.18, 95% CI: 1.06-1.31. Results from the two-sample Mendelian randomization were consistent with these positive associations: OR: 1.06, 95% CI: 0.98-1.15. Conclusions: All three approaches demonstrated a positive association between morning plasma cortisol and incident CVD. Together, these findings suggest that elevated morning cort isol is a causal risk factor for CVD. The current data suggest strategies targeted at lowering cortisol action should be evaluated for their effects on CVD. [ABSTRACT FROM AUTHOR]