Stanford, CA - Dashing hopes of a cheap, natural—some would even say delicious—means of lowering cholesterol, a new study has found no evidence that fresh garlic or garlic supplements can reduce cholesterol levels over a six-month period [1].

"We really thought this would work," lead author Dr Christopher D Gardner (Stanford University, CA) told heartwire. "We thought raw garlic would work and that one of these supplements would probably work, maybe both. . . . We are disappointed we couldn't find something that would help people more."

The study from Gardner et al appears in the February 26, 2007 issue of the Archives of Internal Medicine.

The National Institutes of Health-funded, randomized, controlled trial flies in the face of more than a decade of research supporting the lipid-lowering effects of garlic, not to mention the traditional use of medicinal garlic "since antiquity," the authors, note. But while in vitro and animal studies have shown promising effects on lipids, previous clinical-trial results have been inconsistent and plagued by problems of trial design and funding source. Combining these problematic studies in meta-analyses has only fueled the belief that garlic has cholesterol-lowering properties, Gardner noted.

"There have been five meta-analyses in the past couple of decades that pooled all of the trials, and every one of them said that garlic worked; as a result, the labels of the supplements say that garlic lowers cholesterol on the basis of those studies," Gardner said.

You just can't go out and have an Egg McMuffin for breakfast, a Big Mac for lunch, and a clove of garlic later and think you're okay. That's not the way it works.

The study randomized 192 individuals with moderately elevated cholesterol (with LDL concentrations ranging from 130 to 190 mg/dL) to one of four treatment groups: raw garlic, powdered garlic supplement, aged garlic extract supplement, or placebo. According to Gardner, the two supplements were chosen because they have the most robust evidence behind them and their active components were verified in biochemical testing prior to the study.

During a two-week run-in phase, study participants consumed daily sandwiches prepared by the researchers. During the active phase of the study, participants continued to pick up sandwiches as well as tablets from the coordinating center. In the raw-garlic arm of the study, the sandwiches were prepared with garlic in the condiments, but the tablets were placebo. In the other arms of the study, people picked up sandwiches without garlic, but tablets containing one of the two supplements or placebo.

Over the course of the study, staff at the General Clinical Research Center made more than 30 000 "gourmet, heart-healthy sandwiches," Gardner noted. Blood samples were taken from the study participants every month for six months, when the study ended.

By the end of the study, there were absolutely no changes in LDL from baseline in any of the groups. "It's not like there was a small effect that was not statistically significant," Gardner emphasized. "There was no movement across the six months in any of the four groups. That's what was so disappointing."

The authors also saw no differences effects on HDL, triglycerides, or total cholesterol/HDL ratios.

It is garlic's purported lipid-lowering effects that have been trumpeted the loudest, Gardner noted, adding that for the past five or 10 years, garlic has been in the top-five list for herbal/botanical product sales—perhaps driven by the number of people hoping to lower their LDL.

But Gardner was also careful to emphasize that the study did not evaluate other potential cardiovascular effects of garlic or health benefits beyond the heart. "It's still possible that garlic has an anti-inflammatory effect, or a blood-pressure-lowering effect, or an anticancer effect—all of which should be studied rigorously," he said.

In an accompanying editorial, Drs Mary Charlson and Marcus McFerren (Weill Cornell Medical College, New York, NY) point out that there may even be effects of garlic on atherosclerosis specifically that were not picked up in the study [2]. For one, they argue, Gardner et al's study was based on the premise that allicin is the putative active ingredient, and this may have hindered the ability to consider whether multiple, interactive compounds within garlic might have other effects on atherosclerosis progression.

"I think this is a well-designed trial, with many things taken into account in terms of the availability of allicin, but atherosclerosis is a complex phenomenon that includes a number of drivers other than lipid levels," Charlson told heartwire. "This study is predicated on the thought that allicin is the driver of effect, and I think they've shown that if allicin is the driver of effect, it doesn't affect LDL levels. . . . If you have an elevated LDL and you want to bring it down, garlic is not the solution. But does garlic have any role in preventing atherosclerotic disease? I think the jury is still out."

Gardner et al's study also speaks to the value of publicly funded research into supplements—a multimillion-dollar industry, when the bulk of health claims being made by their manufacturers have not been rigorously studied. "The FDA really wants to regulate supplements, but they get beat down by the lobbyists," Gardner explained. "The studies are expensive and there are so many things out there, we can't test them all. But if the FDA could go after some of the more popular things, like garlic, that have the least substantiation, that would serve us well," he said.

Gardner was also careful to say that garlic may still play a role in heart-healthy diets, if indirectly.

"You just can't go out and have an Egg McMuffin for breakfast, a Big Mac for lunch, and a clove of garlic later and think you're okay. That's not the way it works," Gardner told heartwire. "I really hope the take-home message from this is, if you're going to use garlic, use it in humus on whole-wheat bread, or in an Asian stir-fry full of vegetables, all power to you. That's where garlic is really good for you: do that."