Cholesterol is a fatty substance in the body that is used for many different purposes. It is manufactured by the body and also found in animal products, such as red meat and dairy products.
Cholesterol is found in all parts of the human body. It plays an essential role in the production of hormones and other functions. Cholesterol is a key element in the cell membranes of mammals, and it aids in the production of adrenal and sex hormones and vitamin D. Cholesterol comes from the foods you eat, and is also produced by the liver.
Doctors divide cholesterol into high density lipids (HDL), low density lipids (LDL), and triglycerides. Having too much LDL cholesterol in your blood is a risk factor for heart disease and stroke. Having high levels of triglycerides can also put you at risk of heart disease if you have diabetes. Very high levels of triglycerides can increase your risk of pancreatitis. Figure 01. The excess buildup of cholesterol in the blood is referred to as hypercholesterolemia, which simply means "high cholesterol." Atherosclerosis, or hardening of the arteries, occurs when cholesterol collects and hardens on the walls of the arteries, causing them to thicken and narrow. This narrowing prevents adequate blood supply from reaching the heart. Both diet and medication can help control high cholesterol levels, thereby reducing risk factors for heart disease. Elevation of cholesterol and/or triglycerides is also referred to as hyperlipidemia.
Figure 01. A normal artery and an artery with cholesterol buildup (plaque)
Because fat is not soluble in water, the cholesterol needs a carrier to travel through the blood, a liquid that primarily consists of water. Cholesterol must be transported on fat carrying proteins known as lipoproteins.
There are two different kinds of lipoproteins that you may be aware of that have direct relation to the risk of heart disease: Low density lipoprotein (LDL or "bad cholesterol") and high density lipoprotein (HDL or "good cholesterol"). Both vary in the amount of lipid they carry. Low-density lipoproteins (LDL) often referred to as the "bad cholesterol" carrier, carry about 60% of the cholesterol in the bloodstream. High levels of LDLs can ultimately lead to heart disease because they are the major cause of buildup and blockage in the arteries. At every stage of atherosclerosis (plaque formation in the arteries that can lead to heart attack), high LDL cholesterol worsens the condition. On the other hand, high-density lipoprotein (HDL) may prevent oxidation of LDL and helps prevent the LDLs from sticking to the walls of the arteries and thus prevents the buildup of cholesterol plaque. The lipoprotein carries cholesterol away from the arteries to the liver and adrenal glands. Thus, the goal is to keep the LDL cholesterol low and the HDL cholesterol high.
Elevated cholesterol may be due to genetics. In some individuals, elevated LDL cholesterol levels are due to heredity. These genetic disorders are referred to as familial hypercholesterolemia, familial combined hyperlipidemia, familial defective apolipoprotein B, and polygenic hypercholesterolemia. These disorders are linked to a defect in the way your body handles LDL cholesterol, which leads to high LDL levels.
A diet high in animal fat diet is a major cause of elevated blood cholesterol. Dietary cholesterol plays a large part in raising blood cholesterol levels. This is especially true in North America and Europe, where the diet is heavily based on animal foods, such as meat, egg yolks, poultry, seafood, and milk products. Almost all food from plants, however, such as fruits, vegetables, vegetable oils, grains, cereals, and nuts, do not contain cholesterol. Individual persons, however, vary considerably in their response to a diet high in cholesterol. Some respond with marked increases in total cholesterol and LDL-cholesterol. Others do not respond significantly at all. Currently, we do not have a way to determine the underlying cause of such responses other than observing a trial on a low cholesterol, low saturated fat diet. Very high intakes of dietary cholesterol may be harmful even though blood cholesterol levels do not vary much.
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