Garlic

Clinical Summary

Derived from the bulb or clove of the plant. Garlic is used as a spice and to treat hyperlipidemia, hypertension, atherosclerosis, cancer, and infections. Processing can have a substantial effect on the chemical content in garlic; the volatile oil components are sensitive to heat and certain enzymes are acid-labile. Several oral garlic formulations are available, and clinical studies have addressed a variety of the proposed claims. Placebo-controlled trials repeatedly show a reduction in total cholesterol, LDL-C, and triglycerides at 4-12 weeks with aged or dried garlic preparations. However, sustained response has not been found. Studies evaluating the antithrombotic effects repeatedly have shown modest reduction in platelet aggregation, but varying levels of fibrinolytic activity.

Research shows mixed effects with regard to reductions in blood glucose, blood pressure, or risk of cardiovascular disease. Frequently reported adverse events include bad breath, headache, fatigue, GI upset, diarrhea, sweating, and possible hypoglycemia. Because garlic is known to decrease platelet aggregation and potentially elevate the INR, it should not be used with anticoagulants or in patients with platelet dysfunction. Garlic appears to induce cytochrome p450 3A4 and may enhance metabolism of many medications (e.g. cyclosporine and saquinavir).

 Purported uses

• Atherosclerosis
• Cancer prevention
• Cancer treatment
• Cardiovascular disease
• Circulatory disorders
• High cholesterol
• Hypertension
• Microbial infection
• Skin infections

Mechanism of action

The intact cells of garlic contain an odorless, sulfur-containing amino acid derivative known as alliin. When the cells are crushed, alliin comes into contact with the enzyme alliinase located in neighboring cells and is converted to allicin. Allicin is a potent antibiotic, but it is highly odoriferous and unstable. The ajoenes are apparently responsible for the antithrombotic properties of garlic. Allicin is described as possessing antiplatelet, antibiotic, and antihyperlipidemic activity. Most authorities agree that the best measure of the total activity of garlic is its ability to produce allicin, which, in turn, results in the formation of other active principles. In hyperlipidemia patients, garlic might lower cholesterol levels by acting as an HMG-CoA reductase inhibitor.

For atherosclerosis, garlic is believed to reduce oxidative stress and low-density lipoprotein oxidation and have antithrombotic effects. For hypertension, it is thought to reduce blood pressure by causing smooth muscle relaxation and vasodilatation by activating the production of endothelium-derived relaxation factor. Garlic might stimulate both humoral and cellular immunity, causing T-cell proliferation, restoring suppressed antibody responses , and stimulating macrophage cytotoxicity on tumor cells. Garlic might increase selenium absorption with possible protection against tumororigenesis.