Cholesterol

Dr. Terry Murphy

ED Medical Director

Samaritan Hospital

Cholesterol is a waxy fat-like substance that is an essential component of all the cells of the body. Cholesterol is used to make the walls of every cell, to make hormones such as testosterone and estrogen, to produce vitamin D, to make digestive enzymes, and to “line” nerve cells – sort of like insulation. Without cholesterol the body cannot function properly – so cholesterol is a necessary component of good health. It is only a problem when there is too much cholesterol present in the blood.

Cholesterol gets into our blood in two ways – it is made by the liver, and it is absorbed from the food we eat. The problem is seldom that our liver makes too much cholesterol; rather, too high of a blood cholesterol is almost exclusively from too much dietary intake.

Since cholesterol is a fat (oil) and blood is mainly water; and since oil cannot dissolve in water, the body has developed a unique system to get cholesterol (and all fats) to dissolve in blood. That process involves wrapping the cholesterol in a coat of protein. The combined protein/cholesterol material – called a lipoprotein, dissolves in the blood and can be transported in that form throughout the body.

As it turns out cholesterol can be combined with two types of proteins – one type structurally allows for a lot of cholesterol to “fit” inside the protein shell (high density); while the other does not allow for as many cholesterol molecules to be “packed” into the protein shell (low density). The high density cholesterol lipoprotein (HDL) primarily functions to remove excess cholesterol from the blood, while the low density lipoprotein (LDL) delivers cholesterol to cells for use in making hormones, enzymes or new cells. The net effect is that HDL actively removes cholesterol from the blood – keeping the blood cholesterol level lower; something we consider a good thing. Therefore, we refer to the HDL lipoprotein as “good cholesterol”. Whereas we think of the LDL lipoprotein as “bad” because we know that when LDL is present in excess levels in the blood stream, it tends to “build” up in the inside of arteries causing them to narrow in diameter. This narrowing of the arteries reduces the amount of blood flow through the artery, robbing the surrounding tissues of necessary oxygen. This disease process, known as atherosclerosis, causes injury to the heart, brain, kidneys and other vital organs over time; and can cause strokes, heart attacks, renal and other organ failure.

So when we discuss blood cholesterol, we are actually referring to cholesterol lipoproteins – high density (HDL) and low density (LDL), and their total. Desirable levels of total, HDL, and LDL cholesterol in the blood have been recommended by a number of professional organizations over the years; and with more experience, these recommendations are revised from time to time. Currently these recommendations are for the blood levels to be less than 200 for total cholesterol; below 130 for LDL and above 40 for HDL. If someone has significant risk factors for stroke or heart attack – then we strive for an LDL level less than 100, and greater than 60 for HDL.

A third type of lipoprotein that is discussed occasionally is VLDL – or very low density lipoprotein. This lipoprotein is actually not a cholesterol lipoprotein, but the combination of another type of fat called triglyceride, and protein. While triglycerides are an important form of fat to our body, and must also be “wrapped” in a protein to be soluble in blood; VLDL does not transport cholesterol, and while important as a health measure in a different manner, does not have an effect on blood cholesterol.

Keeping cholesterol levels within the recommended ranges can usually be accomplished with a judicious diet and regular exercise; but sometimes requires medication.

As previously indicated, the main reason for an elevated blood cholesterol level is too much dietary cholesterol intake/absorption, rather than overproduction by the liver. Since cholesterol is present in meat, eggs and hydrogenated fats (trans fats); a diet low in these foods and high in fats from vegetable sources is the mainstay of dietary recommendations. The biggest influence on blood cholesterol levels is the mix of fats in your diet – not the amount of cholesterol you eat. Removing trans fats from the diet and switching to non hydrogenated vegetable oils, is far and away the most important step in managing an elevated blood cholesterol.

Trans fats are made by heating liquid vegetable oils while “bubbling” hydrogen gas through them. This process is called hydrogenization. The subsequent hydrogenated trans fat is converted to a solid, looks more like traditional lard, and can withstand heating better – making it ideal for frying foods.

The average American eats about 6 grams of trans fats per day, whereas a better number would be less than 2 grams, or ideally, 0 grams per day. In fact, it is estimated that for every two percent of calories per day from trans fats (about one order of fast food French fries), coronary atherosclerosis risk increases 23 percent. Further it is estimated that the number of heart attacks per year in the U.S. could be reduced from 6 to 19 percent if trans fats were completely eliminated from our diets.

Additionally, a regular exercise regimen of 30 to 60 minutes several times per week; not only lowers total and LDL cholesterol, it also raises HDL cholesterol levels.

Lastly, there are several well known, well advertised, medications to lower blood cholesterol levels. These can be divided into several types by their mechanisms of action. One group of medications is designed to block absorption of cholesterol by the intestine, causing more cholesterol to pass through without absorption (e.g. Questran, Zetia). Another group is the statin medications (e.g. Lipitor, Mevacor, Pravachol, Crestor and others) which reduce total cholesterol and LDL while raising HDL levels. Lastly, nicotinic acid (Niacin) is most effective at elevating HDL. All three classes of medication can have unpleasant to serious side effects, (flushing, burning skin with Niacin; diarrhea with medications decreasing absorption; and muscle pain or liver disease with statins).

This article is intended to provide useful information, not medical advice. This information cannot, and is not meant to, replace consultation with your physician regarding your individual circumstances.