(USA TODAY) -- A heart disease study presented Sunday is being called a $32 million waste of time -- and even a danger to public health -- by some of the country's leading health experts.

The study tested whether a controversial alternative therapy, called chelation, could reduce heart attacks and other cardiovascular problems in people who already had survived a heart attack.

Chelation therapy, which can remove metals from the blood, is a risky procedure approved to treat rare, life-threatening cases of heavy metal poisoning. Tens of thousands of patients a year have the procedure "off-label," however, paying about $5,000 out-of-pocket, based on the claims of doctors who say it can cure everything from Alzheimer's to autism.

In a presentation Sunday, doctors said the National Institutes of Health-funded trial found a small overall benefit to chelation, mainly because it prevented heart problems in people with diabetes.

Elliott Antman, chairman of the American Heart Association's Scientific Sessions program committee, praises NIH for doing the study.

"Kudos for funding a trial that says, 'OK, if people are lining up to have this done, let's let it undergo rigorous clinical trials,'" Antman says.

Yet some doctors say the study was so badly run that its marginally positive results are meaningless.

Cardiologist Steven Nissen of the Cleveland Clinic says he's concerned the study will encourage more patients to get off-label chelation instead of following advice proven to reduce heart disease.

"This study has the potential to be extremely dangerous," Nissen says, calling it "a poor use of taxpayer dollars."

At least 30 patients have died from chelation therapy since the 1970s, including an autistic 5-year-old Pennsylvania boy, according to a 2008 report in The Medscape Journal of Medicine.

Even the study's lead author says the research is not definitive and should not be used to recommend the practice.

"The most exciting part of this study is that there may be an unexpected signal of benefit," Gervasio Lamas, chief of the Columbia University division of cardiology at Mount Sinai Medical Center in Miami Beach, said in a statement. "We need to understand whether the signal is true, or whether it occurred by chance."

The trial, known as the Trial to Assess Chelation Therapy, or TACT, has been dogged by accusations of safety and ethical problems.

The study was temporarily halted in 2008 because of concerns over ethics and patient safety. An investigation by the federal Office for Human Research Subject Protections found that patients may not have been properly informed of chelation's risks.

In response to such concerns, researchers revised their consent forms, which had failed to mention the procedure's risk of death. Federal officials also ordered researchers to notify patients that the drug they were receiving had not been approved for lead poisoning, as the form suggested, and that the Food and Drug Administration had taken the study drug off its list of approved medications.

About 17% of patients withdrew their consent for the study, so their data cannot be included in the final results, says Stephen Kopecky, a Mayo Clinic cardiologist who participated in the trial. That could seriously skew the results, he says.

Slightly more than 26% of patients given chelation went on to have a cardiovascular problem, compared with 30% of those on placebo. That barely passed a standard test for statistical significance, Kopecky says, and could be explained by the fact that the chelation group began the study with better cholesterol levels.

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