Cholesterol is a naturally occurring substance belonging to a class of compounds known as lipids, which also includes fat, and a number of other, less common substances. Cholesterol is closely associated with fat, but from a physiological and dietary standpoint is quite different and needs to be considered separately.
      The primary role of cholesterol is in the building and maintenance of cell membranes and, in particular, cell tissue in the central nervous system. Additionally, cholesterol is involved in the synthesis of steroid hormones required for metabolic regulation throughout the body.

      The human liver synthesizes from 80~100 percent of the cholesterol the body needs for normal function, the remainder coming from the diet. Dietary cholesterol comes from animal sources alone and, for the most part, includes meats, liver, egg yolks and other dairy products.

      The U.S. Food and Drug Administration (FDA) recommends that average adults should limit their dietary cholesterol to no more than 300 mg per day. Limiting your intake to something less than this figure would be good advice for most adults. Following the recommended intake for fat will assist considerably in accomplishing this goal.

      Cholesterol circulates in the bloodstream bound to larger molecules composed of fat and protein, known as lipoproteins. The two most important forms, in relation to cholesterol, are high-density lipoproteins (HDL) and low-density lipoproteins (LDL). A third form, very low-density lipoproteins (VLDL), is involved primarily with triglycerides.
      The composition of HDL and LDL characterize the effect that cholesterol has on the body. HDL is made up primarily of protein and, in contrast, LDL mostly of cholesterol. The importance of LDL is that it provides the transport mechanism required to deposit cholesterol in the tissues where it performs its normal function. On the down-side, however, excess cholesterol in the LDL fraction alternatively causes these small fatty particles to be deposited on the interior of artery walls. These so-called "plaques" build up over time, eventually blocking the arteries restricting the critical flow of blood. Lack of adequate blood flow to the brain can cause stroke, and if to the heart, heart attacks. This cardiovascular condition, known as atherosclerosis, can be largely prevented by monitoring the level of LDL in the system.
      Occasionally you will hear the terms “good” cholesterol and “bad” cholesterol, referring to the HDL and LDL fractions, respectively. Obviously the bad cholesterol is bad because it contains a far greater amount of circulating cholesterol which is potentially damaging to artery walls. The good, or HDL cholesterol, actually assists to some degree by removing excess fatty deposits from the arteries.

      With the exception of special cases or advice from your health care provider, it is generally agreed that a safe upper limit for blood cholesterol for most adult individuals is 200 mg/dl* (not to be confused with dietary intake of cholesterol). This number alone, however, does not represent the entire picture.
      When measured cholesterol approaches the 200 mg/dl level and, more important, begins to rise above it, the ratio of LDL to HDL that make up that total becomes very important. The U.S. National Institute of Health’s (NIH) National Heart, Lung, and Blood Institute recommends an approximate LDL:HDL ratio of less than 3.5:1 as being desirable. Measured in absolute values, this would be a LDL less than 130.0 mg/dl, and a HDL greater than 35.0 mg/dl. Remember, these are average figures for most adult individuals.

      Maintaining a safe level of cholesterol in the body and, more important, a moderate level of low-density lipoprotein (LDL), can contribute significantly to reduction of risk of cardiovascular disease. While diet is a significant factor in this maintenance, there are other factors to consider. Please see our section on Cholesterol Management for more information.

*  The only way to measure your cholesterol level is by a blood test requested by your health care provider.