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Cholesterol is fatty substance that is a by-product of normal liver metabolism. While many people become alarmed at the mere mention of the word, cholesterol is actually necessary for a number of biological processes. For instance, the body requires cholesterol in order to manufacture vitamin D. It is also needed to produce bile acid to promote proper digestion and to manufacture androgenic hormones. However, there is a key difference between good cholesterol and bad cholesterol.
Since various cells utilize cholesterol, it must be transported through the bloodstream to get where it is needed. This is especially true since cholesterol is insoluble in blood. The vehicle comes in a type of lipid called a lipoprotein. Lipoproteins are designated as being either low-density or high-density. Good cholesterol is also known as HDL cholesterol because its mode of transportation comes from high-density lipoproteins. In contrast, bad cholesterol, or LDL cholesterol, is moved through the blood steam via low-density lipoproteins.
In addition to the mode of transport, there is a difference in destination between good cholesterol and bad cholesterol. LDL cholesterol is considered "bad" because it generally never makes it out of the bloodstream. In fact, it tends to just keep circulating there. This allows cholesterol to collect in arterial walls and eventually form deposits of a hard substance known as plaque. Since the arteries supply blood to the brain and heart, a blockage or narrowing of these routes can significantly increase the risk of a heart attack or stroke.
Good cholesterol, on the other hand, is termed as such because it is carried by high-density lipoproteins. This is meaningful because HDL lipids tend to transport cholesterol out of the arteries and return it to the liver where it is eventually eliminated as waste. In addition, LDL cholesterol left circulating in the bloodstream is often caught up in the process before it has a chance to accumulate and form plaque in the arteries. This is why having a greater serum concentration of good cholesterol is considered beneficial to reducing the risk of heart disease and other complications.
Cholesterol levels in the blood are checked by the measurement of three values: LDL (bad cholesterol), HDL (good cholesterol), and triglycerides, another kind of fat made from unused calories that is also transported via low-density lipoproteins. This blood test may require several hours of fasting first, or else it may not be possible to determine LDL cholesterol and triglycerides levels accurately. Whether or when to have your cholesterol checked depends on a variety of factors, including diet, lifestyle, family history, and age. In addition, high risk factors for heart disease, such as smoking, excessive alcohol consumption, or high blood pressure, may necessitate initial cholesterol testing at an earlier age and with greater frequency after that.
The way I remember which type of cholesterol is which is by looking at the initials. LDL becomes "lousy" in my mind. HDL becomes "healthy".