THURSDAY, Feb. 26, 2015 (HealthDay News) -- Twenty percent of people with heart disease don't respond to cholesterol-lowering statins and may have dangerously clogged arteries, researchers have found.

A new study found these people experienced little or no reduction in the "bad" cholesterol that contributes to artery-blocking plaque, making heart attack or stroke more likely.

The finding has important implications for statin guidelines, said lead researcher Dr. Stephen Nicholls, deputy director of the South Australian Health & Medical Research Institute in Adelaide.

"Cholesterol levels should continue to be monitored to ensure we are moving in the right direction," said Nicholls. "It is simply not good enough to prescribe [a statin] and move on."

The analysis also underscores the need for new medications to target plaque buildup in statin nonresponders, the study said.

Nicholls said many patients -- responders and nonresponders alike -- take low doses of statins, which is not supported by the guidelines. Treating high cholesterol more aggressively is essential to lowering the risk of heart attacks and strokes, he said.

Low-density lipoprotein (LDL) cholesterol -- the bad kind -- leads to thick, hard deposits of plaque that can narrow arteries and make them less flexible.

"Statin therapy has been demonstrated to slow or even reverse progression of plaque along with preventing heart attacks and strokes," said Dr. Gregg Fonarow, a professor of cardiology at the University of California, Los Angeles. "However, response to statins may vary among individuals."

Prior studies have shown that clinical benefits of statin therapy are in direct proportion to how much LDL is reduced, said Fonarow, who was not involved with the study.

He agreed that the findings of this study "suggest it may be important for evaluating clinical response to monitor LDL reduction during statin therapy."

For people who don't respond to statins, there may be hope on the horizon. Fonarow said new drugs to lower LDL cholesterol are being tested in large clinical trials.

For the study -- published Feb. 26 online in the journal Arteriosclerosis, Thrombosis and Vascular Biology -- Nicholls' team analyzed seven studies involving a total of 647 patients with heart disease taking statins. Ultrasound was used to compare the patients' arteries before and after statin therapy. Patients were followed for 18 to 24 months.

Most patients saw significant decreases in LDL cholesterol. However, for 20 percent of the patients, LDL cholesterol levels either decreased only a little, remained the same or increased.

Moreover, these nonresponders had faster plaque buildup in their arteries than patients who responded to statin therapy, the researchers found.

Exactly why so many had a poor response isn't clear, they said.

Guidelines from the American Heart Association recommend statin therapy for:

• People without heart disease, 40 to 75 years old, with some risk for having a heart attack or stroke within 10 years.
• People with a history of heart attack, stroke, angina, artery disease, ministroke, or those who've had angioplasty.
• People 21 and older who have LDL cholesterol of 190 mg/dL or more.
• People 40 to 75 with type 1 or type 2 diabetes.

Others might also benefit from taking statins, but that decision should be made by their doctor.

More information

For more on cholesterol, visit the American Heart Association.