The researchers tested raw garlic and two different garlic supplements on nearly 200 adults with moderately high levels of LDL ("bad") cholesterol. After six months, the patients showed no improvements in their average cholesterol or other blood fats (lipids), no matter what kind of garlic they had consumed.
"Garlic supplements or dietary garlic in reasonable doses are unlikely to produce lipid benefits" in people with moderately high LDL cholesterol levels, write the researchers. But "the jury is still out" about whether garlic prevents heart disease, states an editorial published with the study in the Archives of Internal Medicine.
Poor cholesterol levels are among the risk factors for heart disease.
Cholesterol is measured in milligrams per deciliter (mg/dL). Here are the
optimal levels of cholesterol, according to the National Heart, Lung, and Blood Institute:
The 192 people who took part in the garlic study had less-than-ideal
cholesterol profiles: Their LDL levels ranged from 130-190. Average total cholesterol: about 227.
None had heart disease or diabetes. They didn't smoke and weren't taking any
drugs to treat cholesterol or blood pressure.
Don't know your cholesterol level? A simple blood test can show you where
you rank. Diet, exercise, and medications can help control cholesterol.
The researchers included Stanford University's Christopher Gardner, Ph.D. They gave participants sandwiches to eat and pills to take six days per week for six months.
Participants were split into four groups. One group got sandwiches that included four to six cloves of crushed raw garlic. They took sham supplements containing no garlic or other active ingredients (placebo pills).
Another group got garlic-free sandwiches and took Garlicin, a powdered garlic supplement. The third group got garlic-free sandwiches and took Kyolic, an aged garlic supplement. The fourth group got garlic-free sandwiches and placebo pills.
Extensive tests show that all three forms of garlic contained comparable amounts of allicin, a compound studied for possible anticholesterol effects. Participants had their cholesterol checked monthly throughout the six-month study.
None of the three forms of garlic affected participants' total cholesterol, LDL ("bad") cholesterol, HDL ("good") cholesterol, triglycerides, or other blood fats, the study shows.
"The lack of effect was compelling and clear," Gardner says in a Stanford news release. "The numbers just didn't move. There was no effect with any of these three products, even though fairly high doses were used."
He says the study was large enough and long enough to have detected any cholesterol changes. "We even looked separately at the participants with the highest vs. the lowest LDL cholesterol levels at the start of the study, and the results were identical," Gardner says.
However, the researchers don't rule out the possibility that garlic has health benefits for other groups of people (such as those with higher LDL cholesterol levels) or requires higher doses.
The study's results "do not demonstrate that garlic has no usefulness in the prevention of cardiovascular disease," write the editorialists. They included Marcus McFerren, M.D., Ph.D., of the Center for Complementary and Integrative Medicine at New York's Weill Cornell Medical College.
Many factors affect heart disease, and allicin may not be the only compound in garlic that affects cholesterol, the editorialists suggest.
Garlic supplements are probably safe (no side effects were seen in the study), write McFerren and colleagues. "Do they prevent cardiovascular disease? The jury is still out," the editorialists write.
Gardner's team didn't set out to see if garlic prevented heart disease. The study only tracked cholesterol and other lipid levels.
WebMD contacted the makers of Garlicin and Kyolic for their comments.
"I don't know the exact research protocol for this study," Haru Amagase, Ph.D., director of research and development of Wakunaga of America, which makes Kyolic, tells WebMD.
Amagase says his company's studies show that Kyolic "does not have any influence" on people with normal cholesterol levels, "but if you have a higher cholesterol level, then you might have some reduction" in cholesterol. He also notes that another Kyolic study shows that "our garlic supplement was effective to slow down the plaque formation in a coronary artery," which he says is "much closer" to heart disease.
"Multiple risk factors are deeply involved in cardiovascular disease," Amagase says. "Of course cholesterol is one of the risk factors, but it's not the single risk factor. So we believe that even though it may not have significant cholesterol reduction — I believe it should have moderate cholesterol reduction — but I think other risk factors [are] also important."
Garlicin's maker did not respond in time for publication.
By Miranda Hitti
Reviewed by Louise Chang, M.D.
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