LDL is often referred to as bad cholesterol, although technically LDL is a lipoprotein. Proteins combine with particles of cholesterol forming lipoproteins, which carry the cholesterol through your bloodstream. LDL is responsible for transporting about 75% of your body’s cholesterol to your cells.

The problem with LDL is that it tends to collect on the arterial walls. These LDL deposits may then undergo a process called oxidation. Oxidation is harmful because it makes it easier for LDL cholesterol to penetrate and inflame the arterial walls. In turn, the body’s immune system releases chemicals, called immune factors, to protect the damaged walls of the artery. These immune factors can actually add to the inflammation caused by the LDL, causing even more damage to the arterial walls.

White blood cells and other particles are drawn to the inflammation, causing the build up of plaque in the artery. Eventually the layers of cells that line the blood vessels are injured, and that causes the body to release more immune factors. Unfortunately, the immune factors released in response to the damaged blood vessels increase the risk of blood clots.

The oxidized LDL also reduces the natural production of a substance that’s important for relaxing blood vessels, called nitric oxide. This is harmful, because narrowed vessels limit blood flow and can elevate your blood pressure.

Finally, as the plaques grow, the blood vessels become less elastic and narrower, reducing blood flow to vital organs.

Like LDL, high levels of VLDL, or very low-density lipoprotein, are often considered unhealthy. VLDL can build up in the walls of arteries, contributing to plaque formation. VLDL is comprised mostly of triglycerides, with little protein content. Its primary purpose is to carry triglycerides for storage in fat cells.