Cholesterol

Cholesterol is a fat-like substance that is made by the body and is found naturally in animal foods such as meat, fish, poultry, eggs, and dairy products. Foods high in cholesterol include liver and organ meats, egg yolks, and dairy fats.

Cholesterol is carried in the blood. When cholesterol levels are too high, some of the cholesterol is deposited on the walls of the blood vessels. Over time, the deposits can build up causing the blood vessels to narrow and blood flow to decrease. The cholesterol in food, like saturated fat, tends to raise blood cholesterol, which increases the risk for heart disease. Total blood cholesterol levels above 240 mg/dl are considered high. Levels between 200-239 mg/dl are considered borderline high. Levels under 200 mg/dl are considered desirable. Cholesterol is not a fat, but rather a fat-like substance classified as a lipid. Cholesterol is vital to life and is found in all cell membranes. It is necessary for the production of bile acids and steroid hormones.

Cholesterol is not a life-threatening toxin, but a medium-sized molecule that is really a building block for important parts of the body. In particular it is an essential component of cell membranes. Cholesterol also stabilizes a cell against temperature changes. It is a major part of the membranes of the nervous system, the brain, the spinal cord and the peripheral nerves. In particular it is incorporated into the myelin sheath that insulates the nerves from the surrounding tissue. Cholesterol is also the forerunner of important hormones such as the female sex hormone, oestradiol, and the male sex hormone, testosterone, and of vitamin D, which we need in order to utilize calcium and form bone. Nearly all body tissues are capable of making cholesterol, but the liver and intestines make the most. We require cholesterol to produce the bile we need to digest the fats in our food, and the name itself comes from the Greek words for 'bile solids'.

Cholesterol is so important that together our cells, intestines, and especially our liver make about a gram of it every day. The average adult has 150 grams (5 ounces) in their body, enough to fill a wine glass. Very little of this has come from the cholesterol in their food, and if a person is a vegan vegetarian and eats no animal products, they take in none at all. Their own bodies have to produce all the cholesterol they need. Those who eat meat, fish or dairy products generally consume about half a gram of cholesterol a day, and their body can absorb a little of this. How much depends upon other components of their diet, such as soluble fibre which scavenges cholesterol.

The bloodstream transports cholesterol throughout the body by special carriers called lipoproteins. The two major lipoproteins are low density lipoproteins (LDL) and high density lipoproteins (HDL). LDL is most often referred to as the "bad" cholesterol whereas HDL is knows the "good" cholesterol.

One of the major uses of cholesterol is the synthesis of bile acids. These are synthesized in the liver from cholesterol and are secreted in the bile. They are essential for the absorption of fat from the contents of the intestine. A clue to the importance of cholesterol is that most of the bile acids are not lost in the feces but are reabsorbed from the lower intestine and recycled to the liver. There is some loss, however, and to compensate for this and to meet other needs, the liver synthesizes some 1500-2000 mg of new cholesterol each day. It synthesizes cholesterol from the products of fat metabolism.

There is also an unceasing transport of cholesterol in the blood between the liver and all the other tissues. Most of this cholesterol travels complexed with fatty acids and protein in the form of low density lipoproteins (LDLs). Cells that need cholesterol trap and ingest LDLs by receptor-mediated endocytosis.

Common Names: Cholesterol; Cholesterin
Chemical Name: Cholest-5-en-3ß-ol
Molecular Formula: C27H46O
Molecular Weight: 386.6598