It is difficult to name a single “worst” factor, but from a clinical risk perspective smoking, uncontrolled hypertension, high LDL cholesterol, diabetes, and physical inactivity are among the most powerful drivers. Smoking injures the vessel wall and increases clotting tendency. Hypertension strains the heart muscle over years. High LDL accelerates plaque formation within arteries. Diabetes and insulin resistance damage vascular function and amplify risk. On the nutrition side, ultra-processed foods, trans fats, and high salt–high sugar patterns feed these risk pathways. Chronic stress and poor sleep can also harm indirectly by degrading behavior, recovery, and hormonal balance. The most strategic approach is not to hunt for one enemy, but to manage cumulative risk: regular monitoring, disciplined lifestyle upgrades, and, when indicated, medical therapy working together. That combination is where real prevention lives.