Cholesterol is one of the soft, waxy lipids found in the bloodstream, which is produced in the tissues of all mammalian organisms. An essential lipid, it is also the basis for a wide variety of hormones, as well as other fatty tissue. Although the liver produces all of the cholesterol that the body needs, there are many foods that, when included in the diet, are an additional source. Cholesterol-rich foods include meat, fish, poultry, seafood, egg yolks, as well as a variety of dairy products.
As a hydrophobic, fatty substance, cholesterol cannot transport itself through the bloodstream, so it relies on carriers such as High density lipoproteins, or (HDL), which typically carries approximately one third to a quarter of the body's cholesterol content away from arteries, back to the liver, and finally out of the body. Low density lipoprotein, or LDL, the other major carrier, transports cholesterol to body tissues. In excessive amounts, LDL can block arteries, leading to heart disease.
Several factors contribute to the levels of LDL and HDL in the body. For instance, aerobic exercise, which has long been considered to be an important tool for maintaining cardiovascular health, has been shown to actually increase levels of HDL within the body. Conversely, smoking is said to increase the body's levels of LDL, thereby increasing the risk of heart disease.
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