Cholesterol-lowering statin medications like Lipitor and Crestor have been the most prescribed class of drugs in the U.S. for years.

It's not surprising that statins are so popular. Cardiovascular disease (CVD) is the biggest killer of Americans, and "bad" LDL cholesterol is one of the bad guys in this national tragedy, clogging arteries and triggering heart attacks and strokes.

Taking an LDL-lowering statin is a science-proven strategy for people with diagnosed heart disease or other blood vessel blockages. You're on that list if you have angina or you've had a heart attack, coronary bypass surgery or an artery-widening angioplasty, or a stroke, or you have peripheral arterial disease (clogging of the arteries in the legs).

And possibly if you have diabetes, which damages blood vessels and doubles the risk of heart attack and stroke.

In other words, if you already have CVD, an LDL-lowering statin might save your life through what medical experts call secondary prevention.

But most people who take statins haven't been diagnosed with CVD. A blood test simply showed they had high cholesterol, and their doctor prescribed a statin to prevent a heart attack or stroke — a use medical experts call primary prevention.

Shockingly, a new scientific review of 14 studies shows that statins are virtually useless for primary prevention.

The study was a meta-analysis of scientific literature on primary prevention using statins. A team of UK researchers analyzed data from 14 earlier studies that involved more than 34,000 people. The meta-analysis was published by The Cochrane Collaboration, the most respected scientific review in the world.

Before telling you about the final conclusion of the meta-analysis, it's important to note that the UK researchers faulted the studies in several areas. There was evidence, they said, of "selective reporting of outcomes" — statin-positive results were emphasized, while statin-negative results were ignored (an unfortunately common practice in drug studies).

There was a "failure to report adverse events" — if statins produced side effects, the study authors didn't mention them (another sadly routine feature of pharmaceutical research). And there was "an inclusion of people with cardiovascular disease" in the studies — a sneaky strategy designed to produce positive results, since statins are proven to work in folks with CVD.

Remember, these were studies on primary prevention for people without CVD, not secondary prevention for people with CVD.

The Cochrane scientists then reported the overall results of the 14 studies on statins and primary prevention. The results were not exactly overwhelming.

"Only limited evidence showed that primary prevention with statins may be cost effective and improve patient quality of life," they concluded. "Caution should be taken in prescribing statins for primary prevention among people at low cardiovascular risk."

To put it a little less politely: the millions of people taking statins for primary prevention are taking a drug they don't need!

The downside of statins for primary prevention isn't only that they cost you $1,000 a year and probably don't do you any good. They can also do you a lot of harm.