LDL cholesterol causes artery plaque when LDL particles carry cholesterol from the blood into the inner walls of arteries, where some become trapped. The body responds with inflammation, and immune cells take up the cholesterol and turn into foam cells. Over time, cholesterol, cells, and scar-like tissue build up into plaque. Plaque can narrow an artery or trigger a blood clot if its surface breaks.
What Is LDL Cholesterol, and Why Does It Matter?
Cholesterol is a waxy, fat-like substance that the body needs to build cells and produce certain hormones. Because cholesterol cannot travel freely through the bloodstream, it is carried inside tiny particles called lipoproteins. Low-density lipoprotein (LDL) carries cholesterol to tissues throughout the body, where it can be used by cells.
LDL is often called "bad" cholesterol because higher levels increase the amount of cholesterol carried through the bloodstream and raise the likelihood of plaque forming in artery walls. As MedlinePlus explains, LDL and high-density lipoprotein (HDL) are different types of lipoproteins that help transport cholesterol in the blood. The key issue is not that cholesterol is unnecessary, but that excess LDL can contribute to its buildup in the wrong place.
How Does LDL Cholesterol Turn Into Artery Plaque?
Artery plaque develops through a series of connected events involving cholesterol, the artery wall, and the immune system. This process is called atherosclerosis. It generally progresses over many years, although the rate varies with LDL exposure and other cardiovascular risk factors.
1. LDL particles enter the artery wall
Arteries have a thin inner lining called the endothelium. Beneath it lies a layer of tissue known as the intima. LDL particles circulating in the blood can pass into this inner layer. Some particles become retained in the artery wall instead of returning to the bloodstream. The longer this retention and accumulation continue, the more opportunity there is for plaque to develop.
A consensus statement from the European Atherosclerosis Society identifies the retention of LDL in the artery wall as a central initiating event in atherosclerosis. This helps explain why persistently elevated LDL is important: it increases exposure to the particles that can become trapped in artery tissue.
2. Trapped LDL changes and attracts immune cells
Once retained, LDL particles can undergo chemical changes, including oxidation. These altered particles can activate an inflammatory response in the artery wall. Cells lining the artery release signals that help attract white blood cells, including monocytes, from the bloodstream into the affected area. Once inside the artery wall, monocytes can develop into immune cells called macrophages.
Inflammation is part of the body's normal defense system. In atherosclerosis, however, the continuing presence of retained and modified LDL can keep this response active. The resulting inflammation helps drive the accumulation of cholesterol and other material that contributes to plaque growth.
3. Macrophages absorb cholesterol and become foam cells
Macrophages take up cholesterol-rich particles in an attempt to clear material from the artery wall. When they absorb more lipid than they can effectively manage, they become filled with fat droplets and are called foam cells. These cells are an important feature of early atherosclerotic lesions.
Clusters of foam cells and accumulated lipid can form an early deposit known as a fatty streak. Such deposits are an early stage of atherosclerosis, but not every early lesion will progress at the same rate. When LDL continues to enter and remain in the artery wall, additional cholesterol accumulation and inflammation can contribute to further growth.
4. Cholesterol, cell debris, and connective tissue form a larger plaque
As the process continues, some foam cells die and release their contents. Cholesterol, cell debris, inflammatory cells, and other material can accumulate, forming a lipid-rich core inside the developing plaque. Smooth muscle cells in the artery wall may also move toward the affected area and produce collagen and other structural material. This material can form a fibrous cap over the plaque's core.
Plaque may also accumulate calcium as it develops. According to the National Heart, Lung, and Blood Institute (NHLBI), plaque contains cholesterol, fat, blood cells, and other substances. As it grows, it can narrow the artery and reduce the supply of oxygen-rich blood reaching the tissues beyond it.
How Does Plaque Affect Blood Flow?
Artery plaque affects circulation in two main ways. First, a growing deposit takes up space inside the artery and can reduce the opening through which blood flows. When an artery cannot deliver enough oxygen-rich blood to the tissues it supplies, problems may develop. For example, plaque in the coronary arteries can limit blood flow to the heart muscle, while plaque in arteries supplying the brain or legs can affect those areas.
Second, a plaque can cause a sudden problem even when it has not severely narrowed the artery beforehand. If its surface ruptures or becomes disrupted, blood components involved in clotting can react to the exposed material and form a clot. A large clot can partially or completely block blood flow. The Mayo Clinic explains that plaque buildup can narrow arteries and that a rupture can lead to a blood clot. Depending on the artery involved, this process may result in a heart attack or stroke.
Why Are Some Artery Plaques More Dangerous Than Others?
Not all plaques behave in the same way. Some have a relatively thick fibrous cap that separates the plaque's inner material from the blood. Others have features associated with greater vulnerability, such as a large lipid-rich core, ongoing inflammation, and a thinner cap. These differences matter because a plaque that becomes disrupted can trigger clot formation and abruptly reduce blood flow.
The amount of narrowing alone does not always tell the whole story. A plaque that does not severely restrict blood flow may still cause an acute event if it ruptures and a clot forms. Conversely, a stable plaque may gradually limit circulation without causing a sudden blockage. This is one reason clinicians consider overall cardiovascular risk rather than judging risk from a single feature alone.
What Other Factors Can Increase Plaque Formation?
LDL plays a direct role in atherosclerosis, but other factors can affect the artery wall, inflammation, and a person's overall cardiovascular risk. These factors can contribute to plaque formation or make existing cardiovascular disease more likely to cause complications.
- High blood pressure: Places additional stress on artery walls.
- Smoking and tobacco use: Can damage blood vessels and contribute to cardiovascular risk.
- Diabetes: Is associated with an increased risk of atherosclerotic cardiovascular disease.
- Elevated triglycerides and other abnormal blood lipids: Can contribute to an unhealthy blood lipid profile.
- Inherited factors and family history: Can influence cholesterol levels and the likelihood of developing cardiovascular disease.
- Age and chronic inflammatory conditions: Can also affect a person's risk.
These factors often overlap. For example, a person with elevated LDL and diabetes may have a different overall cardiovascular risk from someone with the same LDL level but no other major risk factors. The relevance of each factor depends on the person's medical history and overall health.
Can Lowering LDL Help Prevent Artery Plaque?
Lowering LDL reduces the amount of cholesterol carried by LDL particles in the bloodstream and can reduce the ongoing contribution of LDL to plaque formation. Managing LDL is therefore an important part of reducing the risk of atherosclerotic cardiovascular disease. The American Heart Association explains that high cholesterol contributes to plaque deposits and that lifestyle changes and, when needed, medicines can help lower cholesterol.
Measures that may help include eating a heart-healthy diet, staying physically active, avoiding tobacco, and managing blood pressure and blood sugar. Some people also need cholesterol-lowering medication, depending on their LDL level, cardiovascular history, and overall risk. A healthcare professional can help determine appropriate LDL goals and whether treatment is needed.
Lowering LDL does not guarantee that existing plaque will disappear. It can, however, reduce ongoing exposure to LDL and help lower cardiovascular risk. The benefit depends on the treatment used, the person's starting risk, and other health factors. A cholesterol blood test measures cholesterol levels in the blood; it does not directly show the amount, location, or stability of plaque inside the arteries.
The Key Takeaway
LDL contributes to artery plaque when cholesterol-carrying particles enter and become trapped in the artery wall. The particles can change, trigger inflammation, and be absorbed by immune cells that become foam cells. As cholesterol, cell debris, and connective tissue accumulate, plaque develops and may grow over time. Plaque can narrow arteries or trigger a clot if its surface is disrupted. Keeping LDL under control helps reduce the risk associated with this process.