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Here's what Wikipedia says about cholesterol. Anyone can find this in one second on the Web.
Cholesterol is a lipidic, waxy steroid found in the cell membranes and transported in the blood plasma of all animals. It is an essential component of mammalian cell membranes, where it is required to establish proper membrane permeability and fluidity. In addition, cholesterol is an important precursor molecule for the biosynthesis of bile acids, steroid hormones, and several fat-soluble vitamins. Cholesterol is the principal sterol synthesized by animals, but small quantities are synthesized in other eukaryotes, such as plants and fungi. It is almost completely absent among prokaryotes, which include bacteria.
The name cholesterol originates from the Greek chole- (bile) and stereos (solid), and the chemical suffix -ol for an alcohol, as François Poulletier de la Salle first identified cholesterol in solid form in gallstones, in 1769. However, it was only in 1815 that chemist Eugène Chevreul named the compound "cholesterine".
Since cholesterol is essential for all animal life, it is primarily synthesized from simpler substances within the body. However, high levels in blood circulation, depending on how it is transported within lipoproteins, are strongly associated with progression of atherosclerosis. For a person of about 68 kg (150 pounds), typical total body cholesterol synthesis is about 1 g (1,000 mg) per day, and total body content is about 35 g. Typical daily additional dietary intake, in the United States and societies with similar dietary patterns, is 200–300 mg. The body compensates for cholesterol intake by reducing the amount synthesized.
Cholesterol is recycled. It is excreted by the liver via the bile into the digestive tract. Typically about 50% of the excreted cholesterol is reabsorbed by the small bowel back into the bloodstream. Intestinal tract absorption is highly selective for cholesterol, excreting plant stanols and sterols (which promote atherosclerosis progression more than cholesterol), back into the intestinal lumen for elimination.
The Big Question
My own serum cholesterol is extremely high (9.5 mmol/L or 366.7 mg/dL) yet I do not have any of the problems supposedly associated with this "condition". Why not? I was tortured for eight years and then almost killed when they lowered my cholesterol. Of course no one wants to know about this.
Winston Churchill: 'Men occasionally stumble over the truth, but most of them pick themselves up and hurry off as if nothing had happened.' To this, I would add that those who learn something are written off as cranks.