Many people in the United States are still not being screened for high levels of so-called bad cholesterol, and when they are found to have it, are often never treated, U.S. researchers said on Tuesday.

They found one in five people in the United States have high levels of LDL or low-density lipoprotein, the bad kind of cholesterol that can build up in the arteries and cause heart attacks and strokes.

And while common medications known as statins, such as AstraZeneca's Crestor or Pfizer Inc's Lipitor, can lower LDL cholesterol and reduce the risk of heart attacks and strokes, nearly two thirds of people in the study with high LDL were never offered these drugs.

We found 60 percent of people with high levels of LDL cholesterol didn't know about these conditions, said Dr. Elena Kuklina of the U.S. Centers for Disease Control and Prevention, whose study appears in the Journal of the American Medical Association.

Kuklina and colleagues studied rates of LDL cholesterol in more than 7,000 adults between 1999-2000 and 2005-2006 who offered cholesterol testing. They also asked participants if they had ever been tested before, and each time, only about 70 percent said they had.

When they looked at the two study periods, they found fewer people had high cholesterol in 2006 -- 21 percent compared to 31.5 percent in 2000. During the same time, statin use rose to 13.4 percent of those studied, from 8 percent in the 1999-2000 period.

That means many people with high LDL were still not being prescribed statins.

I find these results alarming, said Dr. Douglas Weaver of Henry Ford Health System in Detroit and past president of the American College of Cardiology.

Although we are making great strides in cholesterol management in patients with known heart disease, this study shows that many patients who could benefit from lipid-lowering medications and changes in their lifestyle and diet are still going unrecognized, and untreated, Weaver said in a statement.

He said people over 20 need to take it upon themselves to ask for cholesterol screening, and doctors need to be more aggressive about both testing, and treating patients with high levels of LDL cholesterol.