A controversial clinical trial has revealed that chelation therapy slightly reduced the risk of heart attacks and other heart problems. The results of the trial were presented at the annual meeting of the American Heart Association in Los Angeles, California.
Leading researchers questioned the US$31 million study’s findings because, they say, many enrolled patients dropped out of the trial and factors besides the chelation treatment could explain why some patients appeared to benefit.
Moreover, critics contend that there is no scientific rationale behind chelation therapy — which involves repeated infusion of a salt solution intended to sop up metal ions — and ample evidence that the treatment is dangerous. The US National Institutes of Health, the sponsor, suspended the trial in 2008 over safety and other concerns, and it later cancelled another trial testing whether chelation benefited patients with autism (see Agency drops disputed chelation study).
“All of the prior information that we have about chelation therapy suggests that it doesn’t work,” says Kimball Atwood, an anaesthesiologist at Tufts University School of Medicine in Boston, Massachusetts and a vociferous critic of the Trial to Assess Chelation Therpay (TACT). “For both basic science reasons and for the reasons based on whatever clinical trials that have been done before this clinical trial, there was no reason to think that disodium EDTA [the chelating agent used in the trial] had a favourable effect on arthrosclerotic disease.”
Around 100,000 Americans receive chelation therapy for heart disease each year, paying thousands of dollars for the unproven treatment. Proponents say that the treatments reduce the build-up of calcium in atherosclerotic plaques or, alternatively, that they sop up heavy metals that create inflammation-causing free radicals. But Kimball says there is no data to back up either mechanism.
TACT enrolled 1708 patients who had previously suffered a heart attack, short of the nearly 2400 the trial hoped to enroll. About half the patients received an infusion of disodium ethylene diamine tetra acetic acid (disodium EDTA), once a week for 30 weeks, followed by at least ten more infusions every two to eight weeks. The other half received a placebo that also contained sugar. 26% of patients who received chelation therapy went on to suffer cardiac events, including heart attacks, strokes, and death, compared to 30% of the patients on placebo infusions, a difference that was statistically significant.
In a blog post and an interview with Nature, Kimball raised questions about those findings. The beneficial effect of chelation occurred only among patients with diabetes and was more likely to be a statistical fluke because of the low numbers of these patients. He also notes that 79 patients dropped out of the trial, also potentially skewing the validity of the results.
Steve Nissen, a cardiologist at the Cleveland Clinic in Ohio, told that New York Times that the study was “fatally flawed,” and that many of the doctors involved in the trial were on the fringes of medicine.
“We have to look carefully at these unexpected results,” said the study’s principal investigator Gervasio Lamas, of Mount Sinai Medical Center in Miami Beach, Florida, in a press release. “Although not approved by the Food and Drug Administration for treating heart disease, chelation therapy has been used for over 50 years and has generally been believed by conventional medical practitioners and cardiologists to be without value. A definitive answer on chelation therapy will take much additional research…We need to understand whether the signal is true or whether it occurred by chance.”
Lamas declined to comment further when contacted by Nature, pending publication of the trial in a peer-reviewed journal.
Atwood questioned the need for any follow-up work. “It will just be more quackery, mainly a waste of money and time for patients.”