A government-funded study questioning the heart-health benefits of niacin has been criticized by a doctor at the American Heart Association's annual meeting.

Niacin, aka vitamin B3, has long been known to raise levels of "good" HDL cholesterol and lower triglyceride levels. Millions of Americans take niacin believing it reduces the risk of heart attacks and strokes.

The recent study has called into question the benefit of increasing HDL. The 3,400 participants, half of whom had a heart attack prior to the trial, were given Zocor to raise HDL levels, and some were also given Zetia to keep LDL levels low.

The National Heart, Lung and Blood Institute said it stopped the trial early because there was no proven benefit to niacin and an increased risk of stroke. An independent panel reviewed the data collected to that point and concluded niacin offered no heart benefits beyond statins, despite its ability to raise HDL and lower triglyceride levels.

"This trial disturbs me greatly," said Dr. Philip Barter of the Heart Research Institute in Sydney, Australia. The study was not designed to test the benefits of niacin, he said. Any conclusions about niacin should wait until next year, after a larger, 25,000-patient study of a Merck & Co. drug including niacin is completed.

"If that trial doesn't show a positive effect, niacin is finished," Barter added.