Nutrition Action Healthletter
Center for Science in the Public InterestOctober 2000 — U.S. Edition 
Garlic: Case Unclosed

The Bottom Line

 Good studies haven’t consistently shown that garlic lowers cholesterol, blood pressure, or blood sugar, or that it prevents heart attacks, cancer, or blood clots.

 Garlic supplements appear to be safe, but regular users who take prescription blood-thinning medications should let their physicians know.

 Many garlic pills release only small amounts of their active ingredients.

To Garlic Links

Case by Case

Allicin in the Family

Case By Case    “Clinically proven to lower cholesterol.” “Promotes healthy circulation.” “Supports a healthy cardiovascular system.”

   None of these typical claims from garlic supplement labels are backed by good scientific evidence, according to a recent review commissioned by the Agency for Healthcare Research and Quality, part of the U.S. Department of Health and Human Services.

   Gil Ramirez of the San Antonio Evidence-Based Practice Center at the University of Texas was a member of a panel of academic and supplement-industry experts that reviewed 1,800 studies of some of the potential health benefits of garlic. Their conclusions aren’t making garlic-supplement manufacturers smile:

Blood cholesterol. In some studies, garlic supplements lowered high cholesterol levels by about ten percent. But the reduction was seen mainly in studies that lasted three months or less. When Ramirez and his colleagues pooled the results of the eight longer-term studies, they found that people who took garlic supplements for at least six months did not have lower cholesterol levels than people who took look-alike (but garlic-less) placebos.

   Why the contradictory results?

   “We don’t know if garlic just stops working after about three months,” says Ramirez, “or if there was something different about the way the longer-term studies were conducted.”

   The disappointing news about cholesterol shouldn’t have surprised the garlic-supplement industry. While many studies during the 1980s showed that garlic lowered cholesterol, most of the research since then has come up empty...something that many companies have chosen to ignore.

   Take Lichtwer Pharma. It’s the German manufacturer of Kwai, one of the world’s best-selling and most-studied garlic supplements. (The company has sponsored much of the research on garlic and cholesterol.)

   You’ll find the words “Clinically Proven to Lower Cholesterol” on Kwai labels even though five of the company’s six studies since 1995, including both of its U.S. trials, showed that the supplement didn’t lower cholesterol.

   In fact, Lichtwer Pharma continued to tout Kwai’s cholesterol-lowering benefits on labels and in magazine and TV ads while delaying—for three years—publication of its first U.S. study, which flopped.

   Meanwhile, Commission E, the German agency that advises the public and health professionals on herbal medicines, no longer says that garlic lowers cholesterol.

Blood clotting. Many heart attacks or strokes occur when a blood clot gets stuck in a partially clogged artery. In some studies, blood platelets from people who were given garlic supplements took longer to aggregate, or clump together, in a test tube. Aggregation is the first step in forming a blood clot. “But the evidence is too limited to draw firm conclusions about whether garlic prevents blood clots,” says Ramirez.

   A note of caution: “Since garlic might interfere with clotting, people taking blood-thinning medications like Coumadin should let their physicians know if they’re also taking garlic supplements or eating fresh garlic every day,” says Gary Abrams of the University of Alabama at Birmingham.

Heart attacks. “There’s too little evidence to say whether or not garlic prevents heart attacks,” says Ramirez.

Intermittent claudication. Some people feel pain when they walk because the arteries in their legs are clogged. There’s not enough evidence to say whether garlic can help.

Blood pressure. Fourteen of 17 studies found no benefit from garlic. The other three detected small declines of only two to seven percent.

Blood sugar. In 11 of 12 trials, garlic didn’t lower blood sugar levels.

Cancer. When garlic is digested and absorbed, it breaks down into scores of different compounds. Some of them appear to prevent breast, colon, and other tumors if they’re given in large doses to laboratory animals. Does that mean that getting smaller amounts of these compounds from fresh garlic or garlic supplements will do the same for people?

   So far, the evidence isn’t convincing. In a few small studies, patients with laryngeal, stomach, colorectal, or endometrial cancer reported having eaten, years earlier, less garlic than similar people without cancer. But a cancer diagnosis might influence what people eat or remember eating, so these types of “case-control” studies are good only for suggesting possible links between foods or supplements and disease, not for proving cause-and-effect.

   A more reliable but more expensive and time-consuming approach is to monitor healthy people to see if those who eat garlic or take garlic supplements are less likely to get cancer.

   The only completed study to do that looked at 121,000 middle-aged people in the Netherlands. Those who took garlic supplements were just as likely to get breast, colorectal, stomach, or lung cancer over the next three years as those who didn’t.1

   The bottom line: “It’s just too early to say what role garlic may play in helping people avoid cancer,” says Ramirez.

Allicin in the Family

In 1995, when we analyzed nine leading brands of garlic supplements, we found huge differences in the amount of allicin they released. Allicin is the parent of most of the potentially beneficial compounds in garlic. It’s formed when a clove of garlic is crushed or a garlic pill breaks up into pieces in the gastrointestinal tract. Many supplement brands are marketed on the basis of how much allicin they supposedly release. In our 1995 study, one store brand yielded so little allicin that a person would have had to take 44 tablets to get the amount in just one clove of crushed fresh garlic.

   Today, matters may be even worse. A new analysis that simulates what happens to pills in the gastrointestinal tract found that 19 of 23 brands of garlic supplements failed to release more than ten percent of the allicin listed on their labels.

   Larry Lawson, an expert on the chemistry of garlic, found that only one brand—Nature’s Way Garlicin—yielded a substantial amount of allicin. (Lawson, now with a commercial laboratory—Plant Bioactives Research Institute in Orem, Utah—worked for Nature’s Way when he did the study.)

   “Most of the pills were poorly made,” Lawson charges. “They took too long to dissolve, and when they did, they didn’t form much allicin.”

   Another analysis by Lawson discovered that the best-selling Kwai brand yields only one-third as much allicin as it did a decade ago. (The company disputes his results.) According to Lawson, in the mid-1990s the manufacturer changed some of the ingredients in Kwai that may have helped it form allicin.

   “This may explain why, since that time, Kwai has failed to lower cholesterol in published scientific studies,” he says.

   “New clinical trials need to be conducted using well-made garlic supplements that disintegrate properly and release enough allicin to have an effect,” he adds.

   Garlic supplements are available as dried, ground-up powder (like Kwai), as fermented extracts (like Kyolic), or as an oily extract of the fresh cloves.

   “Our review found no convincing evidence that any of these is superior as a source of garlic,” says Ramirez.

1: Carcinogenesis 17: 477, 1996.

David Schardt served on the National Advisory Panel for the recent review of garlic by the Agency for Healthcare Research and Quality.

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