National Garlic Day promotes the many uses of garlic, an edible bulb from a plant in the lily family. Garlic has been used medicinally for thousands of years. It is believed to ward off evil spirits, lower cholesterol and prevent heart attacks and blood clots. The phytochemicals in garlic are believed to be protective against stomach cancer and colorectal cancers.

Garlic is one of the top-selling herbal supplements. Unfortunately, research to date doesn’t prove its worth.

A study published in the Archives of Internal Medicine was the result of work using raw garlic at Stanford University’s Prevention Research Center. One hundred and ninety two adults with moderately high cholesterol were divided into four groups with treatment with raw garlic, powdered garlic supplement, aged garlic extract supplement or a placebo.

The volunteers took the equivalent of one medium-size clove of garlic six days a week for six months. The results: there were no significant effects on LDL cholesterol concentrations or on triglyceride levels, another risk factor for heart disease.

Some research has shown garlic supplements lowered high cholesterol levels by about 10 percent, but the effect only lasted about three months. When the subjects were checked after six months they did not have lower cholesterol levels than people who took the placebo.

One of the most studied garlic supplements is Kwai, made by a German manufacturer. Kwai labels contain the words “clinically proven to lower cholesterol” even though five of the company’s six studies since 1995 showed that the supplement didn’t lower cholesterol. Commission E, the German agency that advises health professionals and the general public on herbal medicines, no longer says that garlic lowers cholesterol.

As far as blood clotting, to date the evidence is too limited to draw firm conclusions as to whether garlic prevents clots. Since garlic might interfere with blood clotting, people taking blood-thinning medications such as Coumadin (warfarin) should let their primary care physician know of their daily garlic consumption.

Fourteen of 17 studies reviewed found no benefit of garlic in lowering blood pressure. The other three studies found small declines of about two to seven percent. To date there is insufficient evidence to say whether garlic prevents heart attacks. Eleven of the 12 studies looking at the impact of garlic on blood sugar found that garlic didn’t lower blood sugar levels at all.

What about garlic’s impact on preventing cancer? When garlic is digested and absorbed into our system it breaks down into many compounds. When given to laboratory rats some of these compounds appear to prevent breast, colon and other tumors, if given in large doses. As for humans, there isn’t convincing evidence that small amounts of these same compounds from fresh garlic or from garlic supplements will do the same.

Crushed garlic contains allicin, which is the parent of most of the potentially beneficial compounds found in garlic. Supplements are often marketed on the basis of how much allicin is released when they are consumed. Testing on many garlic supplements found than 19 of 23 brands tested released less than 10 percent of the allicin listed on their labels. Most of the pills were cited as poorly made, took too long to dissolve and, when they dissolved in a reasonable time, not much allicin was formed.

Researchers advise that to date there is no convincing evidence that any supplements are superior as a source of garlic. The World Health Organization’s guidelines for general health promotion for adults is a daily dose of 2-5 grams of fresh garlic (approximately one clove), 0.4-1.2 grams of dried garlic powder, 2-5 milligrams of garlic oil or other formulations that are equal to 2-5 mgs of allicin per day.

Bottom line: Enjoy garlic in cooking, but don’t rely on it for health benefits. As for warding off evil spirits, the jury is still out.

Georgia Clark-Albert is a registered dietitian and adjunct nutrition instructor at Eastern Maine Community College who lives in Athens. Read more of her columns and post questions at or email her at