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So-called “bad cholesterol” is a lipid naturally present in the body which performs a number of important functions. It is officially known as low density lipoprotein (LDL), and together with high density lipoprotein (HDL) and triglycerides, it combines to create blood cholesterol. Levels of blood cholesterol can be determined with a blood test, in which the total value is determined to provide insight into a patient's general health. A high level of cholesterol is generally perceived as a bad thing, because LDL can cause serious health problems.
The body produces cholesterol in the liver, through the conversation of saturated fats and transfatty acids. It is also possible to elevate cholesterol levels by eating a large amount of dietary cholesterol, cholesterol which is found in animal products. The body needs these lipids to perform various functions including the creation of new cells, making it an important part of the complex system which keeps the human body in good working order.
LDL is known as bad cholesterol because it can tend to accumulate in the walls of the arteries, creating a thick plaque by binding with other substances which float in the blood. Over time, the plaque can harden and cause the artery to narrow, leading to a condition known as atherosclerosis. Narrowed arteries are less able to transport blood, and atherosclerosis can lead to heart attacks and other cardiovascular problems.
By contrast, HDL or good cholesterol appears to reduce the risk of heart attacks because it transports excess cholesterol back to the liver so that the liver can break it down and eliminate it. This is why people are encouraged to eat unsaturated fats and other foods which elevate good cholesterol levels, taking care to avoid or reduce the intake of foods which increase bad cholesterol.
Several things appear to contribute to levels of bad cholesterol in the blood. Diet is the biggest factor, since the body's production levels are limited by the amount of raw materials it can access. The role played by dietary cholesterol appears to be a bit unclear, with some studies suggesting that foods which are high in cholesterol will elevate bad cholesterol levels, while others contradict this claim. Genetics may be involved as well, as are exercise levels. The body will convert consumed fats into energy if asked to do so, while someone who lives a sedentary life will not burn these fats for energy, allowing them to reach the liver for conversion into LDL cholesterol.