Why do our bodies need cholesterol (what does it do)? What happens when our bodies make or intake too much cholesterol? What is the job of lipoproteins? What is LDL cholesterol and what happens if we have too much of it? What does HDL cholesterol do?
fruits, vegetables, and legumes contain no cholesterol.) Although cholesterol is essential to life, we don't need very much of it to keep our bodies running well. Our cells take whatever cholesterol is necessary for maintenance and cell repair and store the excess for future use. The problem is that many of us eat a
diet that is too high in saturated fat and trans fats, and this can stimulate the liver to produce more cholesterol than the body needs.
The connectionbetween high total cholesterol and heart
disease was made in 1961 by the Framingham study. Back then, we didn't have the technology to distinguish between different types of cholesterol particles. That gradually changed, and by 1977 the Framingham study had established a link between an increased risk of heart attack and elevated levels of LDL cholesterol. It was also at this time that we began to
confuse the public with measures of different cholesterol particles and terms like "good" and "bad" cholesterol.
During a discussion with a patient recently, she asked me, "What's the difference between good and bad cholesterol? Isn't it all the same when it's building up in my arteries?" The answer is that it's not the cholesterol itself that is good or bad, but the particles that carry it. These particles are called lipoproteins (thelipo is short for lipid, which meansfat). High-density lipoprotein (HDL) and low-density lipoprotein (LDL) are two of them. It's the protein part of the lipoprotein particle that
acts like a shuttle bus, transporting the cholesterol (and other fats like triglycerides) through your bloodstream to where they are used, stored, or excreted by the body. Lipoproteins are necessary for transporting fats because fat is not soluble in water or in blood.
As it turns out, it's LDL, the so-called "bad" cholesterol, that is doing a lot of the shuttle bus driving. You'd think that this job would make LDL "good." But what makes LDL "bad" is that in excess it can cause us trouble. All cells have special receptors, or binders, that latch onto LDL, pulling it into the cells, where it is used as needed. When these cells have had their fill of
cholesterol, they stop making receptors, which allows the rest of the LDL to stay in the bloodstream. Some of this excess LDL deposits its cholesterol "baggage" in our artery walls —including those of the heart — resulting in the formation of soft atherosclerotic plaques.
The job of clearing the blood vessels of this excess LDL falls to the HDL particles, which is why HDL is often referred to as "good" cholesterol. The makeup of the cholesterol itself in both LDL and HDL particles is the same; it is the direction in which the lipoprotein shuttle bus is driving that determines whether the particle is considered good or bad. HDL is good because it serves as a scavenger, removing LDL cholesterol from the cells and plaques and carrying it back to the liver for excretion in the bile, which empties into the intestine so it can be flushed out of our bodies in our stool. This is called reverse cholesterol transport.