Cholesterol is a white, waxy, fatlike substance. Although we usually think of it as found only in the bloodstream, it is actually present in all tissues in humans and other animals. It is thus present in all foods from animal sources. It it not present in any plants.
Cholesterol is essential to life: among other things, it is used in the outer membranes of cells; as a fatty insulation sheath around nerve fibers; and as a building block for certain hormones.
Despite its importance to life, cholesterol isn’t an essential nutrient—you don’t have to consume any to stay healthy. Most of the cholesterol in your bloodstream is manufactured in your body—primarily by the liver—from the fats, proteins, and carbohydrates you eat.
Just how cholesterol is distributed throughout the body is not entirely clear, but researchers hypothesize that the mechanism works in this way: the liver puts together packages called lipoproteins, made of proteins, cholesterol, and triglycerides (fats either made by the body or derived directly from foods). Low-density lipoprotein, or LDL, carries cholesterol throughout the system, dropping it off where it can be used for cell metabolism. Cholesterol carried by LDL that is not used, broken down by the liver, or excreted is left to circulate in the bloodstream, where it accumulates in the arterial walls. Nodules, called plaques, are eventually formed, decreasing the flow of blood over time—a condition known as atherosclerosis—and favoring the formation of blood clots. This may ultimately cut off the flow of blood; in the coronary arteries, this leads to a heart attack, and in the cerebral arteries, a stroke.
The liver makes another molecular package known as high-density lipoprotein, or HDL. Like the other lipoproteins, HDL is composed of triglycerides, protein, and cholesterol, but HDL carries less cholesterol than LDL. As it circulates through the bloodstream, HDL seems to have the beneficial capacity to pick up cholesterol and bring it back to the liver for reprocessing or excretion.
In simple terms, then, LDL brings cholesterol into the system, so it’s often called “bad” cholesterol, and because HDL clears cholesterol out of the system, it has been dubbed “good” cholesterol. HDL (as well as LDL) is formed only in the body. You can’t eat “good” cholesterol; no type of cholesterol you eat is good for you.
Cholesterol and heart disease
Generally speaking, an elevated total cholesterol level, along with a high LDL level, is associated with an increased risk of heart disease. Low HDL, defined as less than 35 milligrams per deciliter (mg/dl), is also considered a risk factor for heart disease. One study by researchers in Israel and at Case Western Reserve University in Cleveland showed that the risk of dying from heart disease was 38 percent higher in men with HDL under 35, even if their total cholesterol was below 200. Stroke risk in such men was higher, too.
The higher your HDL, the better. An elevated HDL level, defined as 60 mg/dl or more, is considered protective against heart disease. (Female sex hormones tend to raise HDL; this may help explain why women are usually protected against atherosclerosis during their childbearing years, when estrogen production is high.)
Experts believe that to be at low risk for heart disease, adults should reduce their total blood cholesterol levels to less than 200 mg/dl. While there is no magic number—a point at which your blood cholesterol level automatically passes from safe to dangerous—the risk of heart disease rises continually with increasing levels of blood cholesterol, though it doesn’t rise markedly until levels exceed 200 mg/dl. And the rate of coronary heart disease begins to accelerate rapidly above the 220 mg/dl level. Thus, many researchers believe that cholesterol levels should be as low as possible; well below 200 mg/dl is excellent.
Some experts question whether high blood cholesterol levels cause heart disease in everybody, and certainly your cholesterol level needs to be put in perspective within your total risk scenario for heart disease, based on such factors as age, sex, and health habits like exercise levels and whether you smoke. But there is substantial evidence that, in most cases, the connection between high blood cholesterol levels and heart disease is as incontrovertible as the link between smoking and lung cancer. This connection is strongest in men under 50 years of age. For young women and for everybody over 50, the link is weaker but still significant.
The Complete Home Wellness Handbook
John Edward Swartzberg, M.D., F.A.C.P., Sheldon Margen, M.D., and the editors of the UC Berkeley Wellness Letter
Updated by Remedy Health Media