Cholesterol

I

Introduction

Cholesterol, a waxy, fatlike compound that is found throughout the body. Cholesterol is notorious for its role in clogging arteries and thus contributing to heart disease and stroke. But cholesterol is essential to the body, too. It is an important component in cell membranes, and the body uses cholesterol in making sex hormones, adrenal hormones, and vitamin D. Chemically, cholesterol is a complex alcohol of a type known as sterols. It is also a lipid, which means that it does not dissolve in water.

II

Effects of Cholesterol

A close relationship exists among levels of blood cholesterol in the body, those of other fats or lipids, and the development of atherosclerosis (Arteriosclerosis). In this disorder, plaques containing cholesterol are deposited on the walls of arteries, particularly arteries of small and medium size, reducing their inside diameter and the flow of blood. Clotting of blood, such as may occur in the coronary arteries to cause a heart attack, is most likely to develop at places where arterial walls are roughened by such plaques.

Although many foods, particularly dairy products and meat fat, contain cholesterol, the body also synthesizes this sterol in the liver from cholesterol-free substances. Nevertheless, investigation indicates that a cholesterol-rich diet causes abnormally high levels of cholesterol and the related fats and lipids in the blood. Evidence strongly indicates that people with such high levels are more likely to develop atherosclerosis and heart attacks than those with lower levels.

Because cholesterol is insoluble in water, it cannot be carried in solution in the blood. Instead, it is ferried through the bloodstream as part of a complex molecule composed of protein and lipid. Scientists have identified three forms of cholesterol-carrying proteins in the blood: high-density lipoproteins (HDL), low-density lipoproteins (LDL), and very low-density lipoproteins (VLDL). LDL and VLDL appear to promote atherosclerosis, and they are often referred to as “bad cholesterol.” By contrast, HDL appears to retard atherosclerosis, earning it the nickname of the “good cholesterol.” In 1984, the United States National Heart, Lung, and Blood Institute reported results of a study indicating that high levels of bad cholesterol also increased the risk of heart attacks and heart disease.

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III

Improving Cholesterol Levels

People who are born with a predisposition to have abnormally high levels of cholesterol—especially LDL and VLDL cholesterol—can reduce their risk of heart attack by lowering their blood cholesterol. This is done by following a diet low in cholesterol and saturated fats, getting sufficient exercise, and using certain drugs. In 1987, lovastatin, one of a class of drugs called statins that inhibit cholesterol synthesis, was approved for sale in the United States. Many similar drugs are now available. See Nutrition, Human.

A low HDL level also increases the risk of heart disease. Researchers believe that HDL cholesterol carries LDL cholesterol to the liver and helps prevent the formation of arterial plaques. Thus, raising levels of HDL, the so-called good cholesterol, may help prevent atherosclerosis and heart attacks. Regular exercise helps some people raise their HDL levels. Studies suggest that the B vitamin niacin can elevate HDL levels. A long-term study to test the effects of a combination of niacin and a statin on plaque formation and heart disease began in 2006.

IV

Cholesterol and Oil Glands

Cholesterol and its derivatives are secreted through the oil glands of the skin to act as a lubricant and protective covering for the hair and skin. Lanolin, a grease extracted from raw sheep wool and composed largely of cholesterol esters, has a variety of commercial uses in lubricants, leather preservatives, ointments, and cosmetics.

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