High blood cholesterol has been well established as a major risk factor for heart disease--but medical researchers are now recognizing that this is only part of the story. Focusing attention only on high blood cholesterol ignores 50 to 80 percent of the people who will develop heart disease. Half of the nation's 1.5 million heart attacks each year strike people with normal levels of cholesterol.

The full story also involves abnormalities in blood lipids or fats that are more common and more dangerous than high cholesterol. Although elevated cholesterol reflects a high risk of heart disease, normal cholesterol levels do not necessarily reflect low risk.

Understanding Cholesterol

Cholesterol is an important fat necessary for good health and is a crucial building block in the formation of cell membranes, sex hormones and other useful substances. The problem for heart health is when there is too much cholesterol, or more frequently, when the cholesterol is transported in the blood stream by dangerous types of cholesterol-carrying spheres called lipoproteins.

There are many variations in these cholesterol-carrying lipoproteins--variations distinguished by how heavy, or dense, they are. It is the low-density lipoproteins (LDL) that supply cholesterol manufactured by the liver throughout the body. By contrast, high-density lipoproteins (HDL) carry excess cholesterol back from the arteries to the liver for recycling or disposal.

An abundance of LDL cholesterol ("bad cholesterol") contributes to blocked heart arteries while an abundance of HDL cholesterol ("good cholesterol") reduces heart disease risk by removing cholesterol from the arteries. It has long been accepted that elevated LDL and/or low HDL increases heart disease risk and requires appropriate medical treatment.

What's New in the Science of Blood Chemistry

Blood fat assessment of heart attack risk now requires more than just the standard blood cholesterol measurements. Recent studies have shown that it is not just the number of cholesterol particles that determines risk for heart disease, but also the size of these particles. Small, dense LDL are the bad guys that squeeze into the lining of arteries, damage blood vessel walls, lead to the buildup of plaque, and create the possibility of blood clot formation.

Individuals with an abundance of small LDL have 300 percent more heart disease risk than people with large LDL and we now know that certain LDL sub-types (those named LDL IlIa, Illb, and IVb) are most linked to risk at any given LDL level. This helps explain approximately 50 percent of people who suffer a heart attack yet have "normal" blood LDL levels. Similarly, there are five HDL sub-types and one of these (HDL Ilb) appears to be the best-of-the-best and high levels are associated with a lower risk of heart disease.

In addition to density and size, there are other blood fat factors that, when accurately measured, allow physicians to predict with greater accuracy your risk of developing heart disease.

For example, lipoprotein (A), a hairlike projection attached to some LDL particles, seems to foster the formation of blood clots after plaque ruptures from the artery walls. Someone with a low LDL value that previously would have been considered at low risk for developing heart disease, we now know carries a very high risk if there is the presence of lipoprotein A.

Hormone replacement therapy in postmenopausal women with elevated levels of lipoprotein (A) has been shown to reduce these levels and, thereby, reduce the incidence of heart attacks.

What You Can Do

First, consult with your physician. Each individual has a unique set of risk factors and treatment must be matched to individual characteristics. The same treatment is not appropriate for all people.

Lipid disorders are inherited traits that run in families and are often passed from parents to children. Review of a family pedigree can identify individuals who may be at increased risk, allowing the application of preventive cardiology long before the clinical appearance of heart disease. Family members can start preventive steps-including lifestyle changes related to diet, physical activity, weight management and smoking--early in life to prevent or delay the emergence of cardiovascular disease.

The abundance of small LDL and reduced HDL Ilb are part of a heart disease risk profile called the Atherogenic Lipoprotein Profile (or ALP). 'Atherogenic" refers to the tendency of these fat particles to adhere to the walls of your arteries. There is no doubt that elevated LDL cholesterol increases heart attack risk and lowering elevated LDL will be of benefit. There is also no doubt that low HDL cholesterol increases heart attack risk and there is mounting evidence that increasing HDL will reduce this risk.

Lifestyle changes are the foundation of LDL cholesterol reduction and HDL cholesterol increase. In general, exercise and loss of excess body fat are powerful tools to control this disorder. Moderately low fat diets are essential to reducing LDL. Exercise and loss of excess body fat can go a long way in increasing HDL.

Interestingly, a recent finding that appears counterintuitive is that low fat diets may exacerbate ALP. This is not because there is not enough fat in the diet but because when people move to a reduced fat diet, they frequently replace the fat calories with sugars and the modern American diet is awash in sugars.

When diet and exercise prove insufficient, there are numerous medications available to reduce LDL and raise HDL. Consult your physician to determine which are most appropriate for you.