The leading cause of heart disease is atherosclerosis, a gradual buildup of fatty deposits, calcium, and other substances inside the walls of your arteries. This process narrows the blood vessels that supply your heart, reducing blood flow and eventually triggering heart attacks. Heart disease killed over 919,000 Americans in 2023, accounting for roughly 1 in every 3 cardiovascular deaths, and coronary heart disease (the type driven by atherosclerosis) is the most common form.
But atherosclerosis doesn’t happen on its own. It’s driven by a handful of modifiable risk factors, with high cholesterol, high blood pressure, smoking, and chronic inflammation doing the most damage. Researchers estimate that 50 to 90 percent of cardiovascular events could be prevented through lifestyle changes alone, which means the “leading cause” is less a single villain and more a chain reaction you have real power to interrupt.
How Atherosclerosis Develops
Atherosclerosis starts with damage to the inner lining of an artery. This lining, called the endothelium, is a single layer of cells that acts as a barrier between your blood and the artery wall. When that barrier is irritated or weakened by high blood pressure, tobacco chemicals, high blood sugar, or other insults, it becomes permeable. Cholesterol particles in your blood, particularly the LDL (“bad”) type, slip through the damaged lining and lodge in the artery wall.
Once LDL accumulates there, your immune system treats it as a threat. White blood cells rush to the area, swallow the cholesterol, and become bloated “foam cells” that form the core of a fatty streak. Over years or decades, more cholesterol, immune cells, fibrous tissue, and calcium pile on, creating a hardened plaque that narrows the artery. Blood flow to the heart muscle drops, which can cause chest pain during exertion. If a plaque ruptures and a blood clot forms on top of it, the artery can seal shut entirely. That’s a heart attack.
Areas where arteries branch or curve are especially vulnerable. Blood flow at these points becomes turbulent rather than smooth, which weakens the endothelium and gives cholesterol particles more time to infiltrate the wall. This is why plaque tends to form in predictable locations, including the coronary arteries that feed the heart.
High Cholesterol: The Central Driver
Without excess LDL cholesterol in your bloodstream, atherosclerosis struggles to take hold. LDL is the raw material that feeds plaque growth, and lowering it consistently slows or even reverses the process. The American Heart Association considers an LDL level at or below 100 mg/dL optimal for healthy adults. People who maintain that level have significantly lower rates of heart disease and stroke.
For people who already have a history of heart attack or stroke, the target is more aggressive: 70 mg/dL or lower, typically achieved with cholesterol-lowering medication aimed at cutting LDL by at least 50 percent from its starting point. The relationship between LDL and heart disease is dose-dependent. The higher your levels and the longer they stay elevated, the more plaque accumulates.
The Role of Inflammation
Cholesterol buildup is only half the story. Chronic, low-grade inflammation throughout the body accelerates every stage of atherosclerosis, from the initial endothelial damage to the final plaque rupture that causes a heart attack. Inflammation makes plaques less stable by thinning their protective outer cap, increasing the chance they’ll crack open.
Doctors sometimes measure a blood marker called high-sensitivity CRP to gauge vascular inflammation. Studies show that CRP levels reliably predict future cardiovascular events, and that when inflammation drops, plaque volume can actually shrink over time. This is why conditions that fuel systemic inflammation, such as obesity, poorly controlled diabetes, gum disease, and autoimmune disorders, all independently raise heart disease risk.
Other Major Risk Factors
High Blood Pressure
Every heartbeat pushes blood against your artery walls. When that pressure stays elevated, it physically damages the endothelium, creating entry points for LDL. High blood pressure also forces the heart to work harder, causing it to thicken and stiffen over time. It is the single most common coexisting condition in people who develop heart disease.
Smoking
Cigarette smoke contains thousands of chemicals, and research points to free radicals in the smoke as especially destructive to artery linings. These reactive molecules cause both structural and functional damage to endothelial cells, accelerating plaque formation. Nicotine and carbon monoxide contribute too, but the free radical load appears to do the heaviest damage. Quitting smoking begins to reverse vascular injury within weeks.
Metabolic Syndrome and Diabetes
Metabolic syndrome, a cluster of conditions including abdominal obesity, high triglycerides, low HDL cholesterol, high blood pressure, and elevated blood sugar, roughly doubles to triples the risk of ischemic heart disease. In large population studies, men with metabolic syndrome had about 2.4 times the risk and women about 2.3 times the risk compared to those without it. High blood sugar damages blood vessels directly and promotes the kind of chronic inflammation that destabilizes plaques.
How Much Is Preventable
Genetics play a real role. Family history of early heart disease, inherited cholesterol disorders, and certain gene variants all raise baseline risk. But the data consistently shows that lifestyle factors dominate. An estimated 50 to 90 percent of cardiovascular events are preventable through changes in how you eat, move, and manage key health numbers.
The American Heart Association identifies eight core metrics for cardiovascular health:
- Diet quality: emphasizing whole foods, fruits, vegetables, and limiting processed food
- Physical activity: at least 150 minutes of moderate exercise per week
- Tobacco use: not smoking or vaping
- Sleep: consistently getting 7 to 9 hours per night
- Body weight: maintaining a BMI in the healthy range
- Cholesterol: keeping LDL at or below 100 mg/dL
- Blood sugar: maintaining normal fasting glucose levels
- Blood pressure: staying below 120/80 mmHg
Each of these factors acts on the atherosclerosis chain at a different point. Exercise and diet lower LDL and reduce inflammation. Not smoking protects the artery lining. Managing blood pressure reduces the mechanical stress that starts the damage cycle. Sleep deprivation raises blood pressure and inflammation. None of these factors works in isolation, and none is a magic fix on its own, but together they account for the vast majority of preventable risk.
The Global Picture
Cardiovascular disease is the leading cause of death not just in the United States but worldwide. The World Health Organization estimates that 19.8 million people died from cardiovascular disease in 2022, representing about 32 percent of all deaths globally. Of those, 85 percent were caused by heart attacks and strokes, both driven primarily by the same underlying process of atherosclerosis. The pattern holds across high-income and low-income countries alike, though access to prevention and treatment varies enormously.