Cholesterol is a naturally occurring fatty steroid that is found in cell mebranes and blood plasma in all mammals.  It is used to regulate the permiability and fluidity of cell membranes, to form the acidic part of bile, to form some of the other steroid hormones produced by the glands and to help with the use of fat soluble vitamins.  However, if a person's cholesterol levels are too high, atherosclerosis, a type of vasculitis characterised by the deposit of fatty plaque on the body's primary arteries can result. 

Cholesterol is found in many foods, such as cheese, egg yolks, beef, pork, poultry and shrimp.  It is a major component of breast milk and is found in most dairy products, most notably butter.  However, the total intake of all types of fat have more of an impact on the body's level of cholesterol than just the amount of cholesterol alone.  Cholesterol can be synthesized in the liver.  In addition, the body can recycle about half of its cholesterol requirements through the digestion of bile in the intestines.  As such, a shortage of cholesterol in a patient is a rarity. 

Cholesterol is often the main component of gallstones

On House M.D. Edit

In Que Será Será, Lisa Cuddy notes that the patient, George, who is morbidly obese, still has a lower cholesterol level than she does.

In Instant Karma, Robert Chase and Eric Foreman have to come up with an explanation why President Dibala's cholesterol level in his later blood samples were much lower than those in his initial blood samples (the result of Chase actually testing someone else's blood and passing it off as Dibala's).  Gregory House finds out about the deception and finds that Dibala's doctor had prescribed him cholesterol medication which could explain away the results.

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