Cholesterol is a small molecule which is essential to life. It has also been responsible for 17 Nobel Prizes, countless pages of reports in scientific journals and the popular press, and mounting anxiety on the part of health-conscious people. Why? The human body contains about 100 g of cholesterol. It is present in cell walls or membranes everywhere in the body, including the brain, nerves, muscle, skin, liver, intestines, and heart. It is only when cholesterol levels exceed unhealthy amounts that we need to be concerned about lowering cholesterol.
Cholesterol in the blood is controlled in the liver (where cholesterol is produced) and the intestine (where cholesterol is absorbed). Lipids from our diet (cholesterol and triglycerides) are absorbed through the intestines and then are delivered through the bloodstream to the liver, where they are processed. The liver produces and also removes cholesterol from the blood. One of the main jobs of the liver is to make sure all the tissues of the body receive the cholesterol and triglycerides they need to function. Whenever possible (for about 8 hours after a meal), the liver takes up cholesterol from our diet and triglycerides from the bloodstream. During times when dietary lipids are not available, the liver produces cholesterol and triglycerides itself. The liver then packages the cholesterol and triglycerides, along with special proteins, into tiny particles (HDL and LDL) which transports them to and from our body cells. The HDL and LDL are released into the circulation and are delivered to the cells of the body. If the liver produces more cholesterol than the intestines absorb, there will be excess cholesterol in the blood.
Cholesterol is the starting ingredient for the synthesis of the steroid hormones such as progesterone, estrogens, testosterone, cortisol, and aldosterone. The body uses cholesterol to produce many hormones and vitamin D. Cholesterol is also the precursor from which the body synthesizes vitamin D. 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 breakdown.However, the presence of excessive amounts of cholesterol in our bloodstream can lead to atherosclerosis, a condition in which fat and cholesterol are deposited in the walls of the arteries in many parts of the body, including the coronary arteries feeding the heart. In time, narrowing of the coronary arteries by atherosclerosis can produce the signs and symptoms of heart disease, including angina and heart attack. The major culprit seems to be levels of LDLs that are in excess of the body's needs.
Cholesterol in the bile can crystallize to form gall stones that may block the bile ducts. Some foods rich in cholesterol which we should be aware of include liver, kidney, brain, intestine and other organ meat. Crabs, shrimps, lobsters and other shell fish should also be noted. The same applies to the yolk of eggs, butter, corned beef and processed meats. Eating a diet high in plant foods and vegetables and fruits with regular exercises is important in maintaining a healthy lifestyle. We should develop the habits of having a medical check up no matter our state of health at least once a year or once in 2 years.
