After decades of cajoling Americans to know their cholesterol level and get it down as low as possible, the nation's leading heart specialists are changing course.

Cholesterol is still important. But new guidelines published Tuesday afternoon throw out the notion that a specific blood cholesterol level should automatically trigger treatment with cholesterol-lowering drugs.

Also out the window is any notion of treating patients with drugs until their so-called bad cholesterol hits a specific target – one that for most people is all but impossible to achieve by diet alone.

Instead, the new guidelines groups adults into four categories most likely to benefit from cholesterol-lowering drugs. They include people with heart disease and diabetes, as well as people with high levels of LDL cholesterol, the bad kind.

The guidelines also explicitly tell doctors not to bother with drugs other than statins, saying they're the only ones proven to reduce the risk of heart attacks and strokes.

The effect of the new guidelines would be to double the number of Americans who are candidates for lifelong statin therapy, according to Dr. Sidney Smith of the University of North Carolina, one of the guideline writers.

Nobody knows for sure how many Americans are already taking statin drugs. Under the old guidelines, 15 percent of adults are recommended for treatment, or about 15 million people. A doubling of that would be 30 million. But by some estimates, the number currently taking statins may already approach that number.

"It may be there are a substantial number of patients now on statin therapy where there is not strong evidence of benefit," Smith tells Shots. "The new guidelines will treat better and smarter, focusing on populations most likely to benefit."

Statin drugs marketed in the United States include brand names such as Crestor, and generic versions of Lipitor and Zocor. They cost from $4 to $150 per month.

The new guidelines were developed jointly by the American College of Cardiology and the American Heart Association, at the behest of the National Heart, Lung and Blood Institute, a federal agency. They are based on the most up-to-date research on prevention of heart attacks and strokes.

The new guidelines will pay off, Smith says, in a sizable reduction in Americans suffering and dying from cardiovascular diseases.

"It's clear we need to treat more patients, because we have a big problem and we're not getting there now," Smith says. "At a time when one out of three Americans are dying of heart attacks and strokes, these guidelines offer a way forward to more precisely identify the patients" who need to get statin therapy.

But the new way forward is more complex than the current advice. Under the National Cholesterol Education Program guidelines, people whose bad cholesterol is above 130 milligrams per deciliter of blood should get cholesterol-lowering drugs to lower their levels to below 100.

In recent years, the push has been to go as low as possible with LDL, with targets as low as 60 to 70, a level usually not possible to achieve without statin drugs.

One main reason why the number of Americans on statin treatments could double if the new guidelines were actually followed is that people without known cardiovascular disease or diabetes would now be considered for statin treatment if their 10-year risk of heart attack or stroke is more than 7.5 percent.

One of the previous thresholds for cholesterol-lowering drug therapy was a 10-year risk of 20 percent. "That's a big driver, the changing of the threshold," Smith says.

In addition, the guideline panel has come up with a brand-new way of calculating the 10-year risk, replacing a widely used risk calculator derived from the famous .

The new calculator takes into account the risk of stroke, while the Framingham Risk Calculator doesn't.

Other than healthy people with a 7.5 percent 10-year risk, there are three other groups that ought to be considered for statin treatment under the new guidelines:

For people over 75 who also have risk factors, the guidelines recommends moderate doses of a statin drug. Those at greater risk should get aggressive therapy, but the new guidelines don't specify an LDL target that older patients should achieve.

The guidelines stress the importance of a healthful diet, weight loss, exercise and blood pressure control in addition to statin treatment. But there's no doubt that the overall effect, to the extent the guidelines are followed, will be to put many more people on cholesterol-lowering drugs.

In borderline cases where doctors aren't certain whether to write a statin prescription, the new guidelines say they should take into account a patient's family history of heart disease and stroke and also consider ordering tests that can indicate underlying artery disease.

These tests include a CT scan for coronary artery calcium levels that measures the degree to which the heart's arteries are clogged; a blood protein called CRP that indicates chronic inflammation; and a test for blood flow in the brachial artery of the ankle, which indicates whether leg arteries are narrowed by atherosclerosis.

Around 5 percent of patients taking statin drugs get muscle aches and pains, and a much smaller proportion can have serious muscle damage. Some of these patients have taken alternative cholesterol-lowering drugs that the new guidelines say are ineffective in lowering cardiovascular risk. The hope, specialists say, is that nearly all muscular side effects can be minimized by lowering the statin dose or switching to a different statin.

The new guidelines are clearly more complex, so it's not clear how readily patients and doctors will adopt them.

"This is a tectonic shift in thinking that's hard to explain," says Dr. Steven Nissen of the Cleveland Clinic, a leading cholesterol expert who wasn't involved in writing the new guidelines.

Nissen is generally supportive of the new guidelines, but he predicts they'll be controversial and difficult to understand.

"I worry about this causing confusion, because we've been telling patients for two decades, 'know your numbers' and 'treat to a certain level,' " Nissen tells Shots. "There will be some significant confusion until we educate everybody about what we are asking them to do."

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