Contrary to the widespread belief that garlic pills are nature's very own cholesterol buster, an unusually rigorous clinical study made public today found that the supplements did not lower blood cholesterol levels at all.
The research, published in the Journal of the American Medical Assn., undercuts the prime reason that garlic appears to be the nation's most popular herbal or botanical supplement. Americans spent $71 million on medicinal garlic preparations in 1997, up 11% from the year before.
That growing appetite is largely based on several previous clinical studies suggesting that whole garlic or garlic pills can lower moderately elevated blood cholesterol levels 10% to 15% or more.
Seizing on those results, everyone from supplement makers to cookbook authors have promoted the herb as a sure-fire alternative to pharmaceutical drugs. "Garlic is a powerful cholesterol-lowering substance," declares the 1998 book Prescription Alternatives.
Many medical researchers have also taken garlic's prowess for granted. Indeed, the new study, involving 25 people in Germany who alternately took a commercial garlic supplement and a dummy pill for three months, was intended to study how it lowered cholesterol levels, not whether it did so.
"We were surprised that the overall effect of the garlic drug on cholesterol was zero," said the study's lead author, Dr. Heiner Berthold, a clinical pharmacologist at the University of Bonn. The garlic pills tested had active ingredients equivalent to four to five grams of fresh garlic, or a few medium-sized cloves.
"It looks like an extremely good study," said Dr. Frank Sacks, a medical nutritionist and cholesterol expert at the Harvard School of Public Health. Most significant, he said, the study was so rigorously designed that it would have detected even a slight effect of the garlic pills on blood cholesterol.
A Lesson for the Public
This garlicky turnaround highlights the difficulty that physicians and lay people alike have in translating modest clinical findings into sound advice to live by. "It's an object lesson for consumers to use caution when dealing with unsubstantiated treatments," Sacks said.
Representatives of supplement makers interviewed by The Times disputed the study's broad significance, saying that it pertained only to the garlic oil formulation tested. Other, dried garlic preparations, not to mention whole fresh garlic, may contain ingredients that are crucial to the herb's reported benefits, they said.
But Berthold said that the product tested, a pill containing oils purified by a steam distillation process, was loaded with the same basic active ingredients found in powdered garlic preparations, including allicin, which serves as the standard of nearly all garlic supplements.
Moreover, another new study of 28 people who took a commercial brand of dried garlic pills for three months at the recommended dosage also found that the supplement did not lower blood cholesterol, a type of lipid.
"This study does not support the use of garlic tablets for lowering plasma lipid levels," concluded the researchers, who were led by Dr. Jonathan Isaacsohn, now at the Metabolic and Atherosclerosis Research Center in Cincinnati.
That study, published last week in the Archives of Internal Medicine, an AMA journal, involved a popular dried garlic supplement, Kwai, and was paid for by the supplement's maker, Lichtwer Pharma of Germany.
The technical manager of the company's United Kingdom unit said in an interview that he was not aware of the negative findings. Neither was the research director of Nature's Way, a Springville, Utah, company that makes the powdered garlic supplement Garlicin.
To be sure, the new studies do not address other properties of garlic associated with cardiovascular health. There is some evidence that it can lower blood pressure slightly and thin the blood in a way that might reduce the risk of clogged arteries. It is also said to kill germs, and may slow the growth of cancer cells.
Still, consumers embraced garlic primarily for its effects on blood cholesterol, which is associated with increased risk of heart disease when extremely elevated.
"I can't help but think that garlic has some positive effects when mixed into a healthy diet," said Dr. David Heber, head of UCLA's Center for Human Nutrition. Although he recommends garlic supplements to improve blood cholesterol levels in his 1998 book, "Natural Remedies for a Healthy Heart," he said in an interview that he never thought garlic pills alone should be used to treat cholesterol problems.
What makes the new German study significant, experts said, was its scrupulous design. The 25 subjects had moderate to high cholesterol levels, ranging from 240 to 348 milligrams per deciliter. They received a placebo for three months and a garlic supplement for three months, with a one month "wash out" period in between when they again took just the placebo. Blood samples were repeatedly taken for cholesterol measurements.
During the main treatment periods, the subjects and the researchers were "blinded" to whether a placebo or supplement was being administered.
After six months, there was no difference in cholesterol levels between the two groups.
Supplements may have had an undeserved positive reputation, Berthold said, because industry-supported researchers may have been disinclined to publish negative results. As a result, summaries of the evidence may appear more positive than the totality of evidence would indicate.
"Taking garlic preparations can give people a false sense of security that they are doing something beneficial for themselves when perhaps they should be taking an effective pharmaceutical drug," Berthold said.