updated 5/26/2011 11:26:54 AM ET 2011-05-26T15:26:54

The U.S. National Institutes of Health on Thursday halted a major study of high-dose niacin, a type of B vitamin, more than a year ahead of schedule because of the lack of benefit. It was the latest setback in the quest to harness good cholesterol to fight the bad kind.

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LDL cholesterol is the main source of artery clogs. Popular statin drugs — sold under such names as Zocor and Lipitor, plus generic forms — are mainstays in lowering LDL. Yet many statin users still suffer heart attacks, because LDL isn't the whole story. Low levels of HDL, the good kind that helps prevent artery clogs, as well as too many triglycerides, a different fat, also increase heart risk.

So scientists are testing whether adding various drugs to statins would increase HDL enough to protect the heart.

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The newest study tested Abbott Laboratories' Niaspan, an extended-release form of niacin that is a far higher dose than is found in dietary supplements. The drug has been sold for years, and previous studies have shown it does boost HDL levels.

More than 3,400 statin users in the U.S. and Canada — people still at risk of a heart attack because of low HDL levels — were given either Niaspan or a dummy pill to add to their daily medicine.

As expected, the Niaspan users saw their HDL levels rise, and their levels of risky triglycerides drop, more than people who took a statin alone. But the combination treatment didn't reduce heart attacks, strokes or the need for artery-clearing procedures such as angioplasty, the NIH said.

That finding "is unexpected and a striking contrast to the results of previous trials," said Dr. Jeffrey Probstfield of the University of Washington, who helped lead the study.

Also, there was a small increase in strokes in the high-dose niacin users — 28 among those 1,718 people given Niaspan compared with 12 among the 1,696 placebo users. The NIH said it was not clear if that small difference was merely a coincidence, as previous studies have shown no stroke risk from niacin. In fact, some of the strokes occurred after the Niaspan users quit taking that drug. Researchers said patients shouldn't stop taking their Niaspan without talking to a doctor first.

Two other HDL-raising drugs have failed to prevent heart attacks when put to stringent tests, raising questions about this strategy. But the NIH noted that several other large studies testing the HDL-raising drugs, including another international niacin study, are under way.

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