Sometimes people have the idea that all cholesterol（膽固醇）in the blood is bad. But the body needs this fatty substance to create cells and hormones. The liver produces all the cholesterol we need.

Low-density lipoprotein（脂蛋白）, or L.D.L., carries cholesterol into the blood. L.D.L. that is not used by cells is called "bad" cholesterol. High-density lipoprotein, H.D.L., is considered "good." H.D.L. gathers up the unused cholesterol and moves it back to the liver. The liver then destroys it.

If L.D.L. levels are too high, then the blood has more cholesterol than the H.D.L. can remove. The extra cholesterol sticks to the inside of the arteries（動(dòng)脈）. This can restrict blood flow or cause blockages that result in heart attacks and strokes. For this reason, doctors often place more importance on high levels of H.D.L., the good cholesterol.

But new research questions this way of thinking. Daniel Rader is a professor who does cholesterol research at the University of Pennsylvania School of Medicine. Doctor Rader agrees that high H.D.L. is a good thing. In general, he says, people with higher levels of good cholesterol have less chance of a heart attack.

Yet many doctors see patients with high levels of both good and bad cholesterol. These patients may not receive drugs to lower their bad cholesterol because their H.D.L. level is high. Such drugs are called statins. But Doctor Rader says high H.D.L. alone does not provide enough protection.

Currently doctors are told to treat patients with heart disease or diabetes until their L.D.L. is below a level of one-hundred. But Doctor Radar notes new findings that even this may not be low enough to protect against heart attack or stroke.

Doctors know that lowering bad cholesterol reduces the risk of heart attacks. But the new study shows that lowering it more aggressively lowers that risk even more.

The findings are from a study called PROVE-IT. The study was released at a meeting of the American College of Cardiology. A report will appear in the New England Journal of Medicine.

The risk of heart disease increases in people who smoke tobacco, weigh too much or do not exercise. Other influences are high blood pressure, age and family history.

This Special English Health Report was written by Jerilyn Watson.