The Lowdown on Cholesterol

Learn the differences between 'good' and 'bad' cholesterol. 

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You may wonder why, if cholesterol is so bad for you, it is present in your body in the first place. The answer is that cholesterol is not all bad and is, in fact, necessary for life. Your liver manufactures cholesterol for a reason: It is essential for the production of cell membranes and sex hormones, such as estrogen and testosterone. Cholesterol is even added to infant formula because it's necessary for normal growth and development. We also obtain cholesterol from animal food sources, such as dairy and meat. (Plant foods like 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 connection between 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 (the lipo is short for lipid, which means fat). 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.
How Much Cholesterol Is Too Much?
The Standard Lipid Profile, the heart disease screening lab test used by most doctors, measures your total cholesterol, HDL ("good") cholesterol, LDL ("bad") cholesterol, and triglycerides. In the mid-1980s, the federal government and the American Heart Association joined forces to create the National Cholesterol Education Program (NCEP) to educate the public about the importance of maintaining normal cholesterol. Based on the NCEP guidelines, total cholesterol should be 200 mg/dL or less for everyone. What follows are the NCEP guidelines for LDL, HDL, and triglycerides.
                                                     Posted By:-R.N.A
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