Over the last 40 years, heart specialists have learned a lot about the way cholesterol behaves in the body, much to the benefit of Americans destined to suffer heart attacks or strokes - at least half of the population.

As knowledge has grown, the goals of treatment have changed, with lifesaving effects. And now they are changing again.

At first, pioneers bent on preventing cardiovascular disease focused only on a person's total blood cholesterol level. A level of 240 milligrams per deciliter of blood serum was considered "normal" just a few decades ago. Then research showed that at least half of heart attack victims had cholesterol levels of 240 or below.

Today, the goal for total cholesterol is 200 or less, preferably 180 if you want to remain heart-healthy.

As the chemistry and physiology of cholesterol became better understood through the work of scientists like Dr. Michael S. Brown and Dr. Joseph L. Goldstein, who shared a Nobel Prize in medicine in 1985, attention shifted to low-density lipoprotein cholesterol, or LDL, the so-called bad cholesterol. When LDL is oxidized, it becomes glued to the lining of arteries that feed the heart, brain, and tissues throughout the body, setting the stage for a heart attack or stroke.

Based on current recommendations, people otherwise at low risk for heart disease should have an LDL level of less than 130. For someone known to be at high risk or who already has heart disease, the desirable level of LDL is much lower, well below 100.

The statin drugs have revolutionized the treatment of elevated LDL.

But the statins don't do much for the newest, and perhaps more important, focus of concern about cholesterol. It is the level of high-density lipoproteins, or HDL, a reverse carrier of cholesterol. HDL, often referred to as the good cholesterol, acts like an arterial Roto-Rooter, clearing cholesterol from blood vessels and routing it to the liver for elimination from the body.

Unlike LDL, which should be as low as possible, the higher the blood level of HDL, the better, even if it means raising your total cholesterol level above 200. Low levels of HDL - below about 40 milligrams for men and 50 for women - are associated with an increased risk of cardiovascular disease. People with "longevity syndrome," who live into their 90s without evidence of heart disease, typically have very high levels of HDL.