Health benefits and concerns

Atherosclerosis

Many actions associated with garlic supplements may help prevent or potentially alleviate atherosclerosis. Garlic has been shown to prevent atherosclerosis in a four-year double-blind trial. The preparation used provided 900 mg of garlic powder per day, standardized to contain 0.6% allicin. The people in this trial were 50 to 80 years old, and the benefits were most notable in women. This trial points to the long-term benefits of garlic to both prevent and possibly slow the progression of atherosclerosis in people at risk.

Garlic also decreases excessive blood coagulation. It has been shown in double-blind and other controlled trials to decrease the overactive coagulation of blood that may contribute to atherosclerosis.

Athlete’s foot

The compound known as ajoene, found in garlic, is an antifungal agent. In a group of 34 people using a 0.4% ajoene cream applied once per day, 79% of them saw complete clearing of athlete’s foot after one week. The rest saw complete clearing within two weeks. All participants remained cured three months later. One trial found a 1% ajoene cream to be more effective than the standard topical drug terbinafine for treating athlete’s foot. Ajoene cream is not yet available commercially, but topical application of crushed, raw garlic may be a potential alternative application.

Chronic candidiasis

Garlic has demonstrated significant activity against the common yeast germ (Candida albicans) in animal studies. Greater anti-candida activity has resulted from exposing candida to garlic than to nystatin, the most common prescription drug used to fight candida. No clinical studies of garlic in the treatment of candidiasis have yet been conducted. However, some doctors suggest an intake equal to approximately one clove (4 grams) of fresh garlic per day. This would equivalent to consumption of a garlic tablet that provides a total allicin potential of 4,000 to 5,000 mcg.

Colon cancer

Garlic belongs to the group of plants known as Allium. Preliminary studies have investigated the association between eating Allium herbs and the incidence of cancer. The most consistent data come from research focusing on the protective effects of Allium consumption against cancers of the gastrointestinal tract. Several preliminary studies have found that people who consume more Allium vegetables appear to have a reduced risk of colon cancer and precancerous colon polyps. Constituents in garlic prevent the conversion of nitrates (compounds found in vegetables and, to a lesser extent, in water) to cancer-causing nitrites and nitrosamines.

Common cold

Herbs, such as garlic, that stimulate the immune system to fight infections are used at the onset of the common cold. In a double-blind trial, participants took one capsule per day of a placebo or a garlic supplement that contained stabilized allicin (the amount of garlic per capsule was not specified) for 12 weeks between November and February. During that time, the garlic group had 63% fewer colds and 70% fewer days ill than did the placebo group.

Ear infections (recurrent)

Ear drops with mullein, St. John’s wort, and garlic in an oil or glycerin base are traditional remedies used to alleviate symptoms, particularly pain, during acute ear infections. No clinical trials have investigated the effects of these herbs in people with ear infections. Moreover, oil preparations may obscure a physician’s view of the ear drum and should only be used with a healthcare professional’s directions.

High blood pressure

Garlic has a mild blood pressure-lowering effect, according to an analysis of ten double-blind trials. All of these trials administered garlic for at least four weeks, typically using 600 to 900 mg of garlic extract per day.

High cholesterol

Eating garlic has helped to lower cholesterol in some research, though several double-blind trials have not found garlic supplements to be effective in this way. Although some of the negative reports have been criticized, the relationship between garlic and cholesterol lowering remains unproven. However, garlic is known to act as a blood thinner and may reduce other risk factors for heart disease.

An analysis of many double-blind garlic trials performed through 1998 suggested that cholesterol was lowered by an average of 9 to 12% over a one- to four-month period. Most of these trials used 600 to 900 mg per day of garlic supplements. More recently, however, several double-blind trials have found garlic to have minimal success in lowering cholesterol. One negative trial has been criticized for using a steam-distilled garlic “oil” that has no track record for this purpose, while the others used the same standardized garlic products as the previous positive trials. Based on these findings, the use of garlic should not be considered a primary approach to lowering high cholesterol.

Part of the confusion may result from differing effects from dissimilar garlic products. In most but not all trials, aged garlic extracts and garlic oil (both containing no allicin) have not lowered cholesterol levels in humans. Therefore, neither of these supplements can be recommended at this time for cholesterol lowering. Odor-controlled, enteric-coated tablets standardized for allicin content are available and, in some trials, appear more promising. Doctors typically recommend 900 mg per day (providing 5,000 to 6,000 mcg of allicin), divided into two or three administrations.

High triglycerides

Omega-3 fatty acids from fish oil and cod liver oil have been reported to affect blood in many ways that might lower the risk of heart disease. However, these supplements sometimes increase LDL cholesterol—the bad form of cholesterol. Research shows that when 900 mg per day of garlic extract is added to fish oil, the combination dramatically lowers triglyceride (TG) levels but no longer increases LDL cholesterol. Taking garlic supplements may be a way to avoid the increase in LDL cholesterol sometimes associated with taking fish oil. A doctor can check to see if fish oil has this effect on an individual.

An analysis of many clinical trials of garlic performed until 1998 suggested that triglycerides were lowered by an average of 8 to 27% over a one- to four-month period. Most of these trials used 600 to 900 mg per day of a garlic supplement standardized to alliin content and allicin potential. More recently, however, three double-blind clinical trials have found garlic to have minimal success in lowering triglycerides One negative trial has been criticized for using a steam distilled garlic “oil” that has no track record for this purpose, while the others used the same standardized garlic products as the previous positive clinical trials. Based on these findings, the use of garlic should not be considered a primary approach to lowering high triglycerides. However, odor-controlled, enteric-coated garlic tablets standardized for allicin content can be taken in the amount of 900 mg per day (providing 5,000 to 6,000 mcg of allicin), divided into two or three daily portions.

HIV support

Garlic may assist in combating opportunistic infections. In one trial, administration of an aged garlic extract reduced the number of infections and relieved diarrhea in a group of patients with AIDS. Garlic’s active constituents have also been shown to kill HIV in the test tube, though these results have not been confirmed in human trials.

Infection

Garlic is considered to be an antimicrobial herb, one that directly attacks various microorganisms.

Intermittent claudication

A standardized extract of garlic has been tested as a treatment for intermittent claudication. In a double-blind trial, the increase in walking distance was significantly greater in people receiving garlic powder extract (400 mg twice per day for 12 weeks) than in those given a placebo.

Parasites

Garlic has been demonstrated to kill parasites, including amoeba and hookworm, in test tubes and in animals. Older studies in humans support the use of garlic to treat roundworm, pinworm, and hookworm. However, due to a lack of clinical trials, the amount of garlic needed to treat intestinal parasites in humans is not known.

Sickle cell anemia

In a preliminary trial, 20 patients with sickle cell anemia were given either 1 mg of folic acid per day or folic acid plus 6 grams of aged garlic extract, 6 grams of vitamin C, and 1,200 mg of vitamin E daily for six months. Patients taking the combination had a significant improvement in their hematocrit (an index of anemia) and less painful crises than did those taking just folic acid. Additional research is needed to determine what role, if any, garlic played in that improvement.

Health benefits and concerns for vegetables
Many health benefits and concerns associated with this food are applicable to other vegetables. Read about health benefits and concerns for vegetables for a full description.