Garlic, used throughout the world as a zesty cooking additive, is also widely recognized for its health benefits. Studies have indicated that regular consumption of garlic (allii sativi bulbus) can lower cholesterol and triglyceride levels, help prevent atherosclerosis and heart disease, and reduce the risk of heart attack or stroke.

Garlic is a root crop related to the onion, with the edible head, or “bulb,” growing underground. The bulbs consist of cloves, which can be easily cut or crushed for cooking purposes or processed into an extract for dietary supplementation.

Background

Garlic has a long history of medicinal use.1 The oldest medical text on record, the Codex Ebers, written in 1550 bc, mentions garlic as a source of endurance and strength. Ancient Romans and Greeks valued garlic’s qualities. Athletes and soldiers consumed it for strength enhancement, and soldiers used poultices of the herb to disinfect and treat wounds. In 77 ad, Pliny the Elder wrote the 10-volume encyclopedia Naturalis Historia, in which he listed garlic as a remedy for some 61 ailments.1 By the 6th century BC, the herb was being used in China and India for therapeutic purposes, and later, Native Americans adopted it for a variety of folk treatments.

It wasn’t until the late 19th century that garlic’s benefits were scientifically scrutinized. In 1858, Louis Pasteur demonstrated garlic’s antibacterial properties, and in World War I, it was used when bandaging wounds.1 Garlic was used in World War II to prevent septic poisoning and gangrene.

Today, scientists are focusing their research on garlic’s cardiovascular (CV) effects. Cholesterol-lowering actions as well as anti-platelet aggregation properties make garlic a modern, popular herbal preparation.2

Efficacy

A meta-analysis performed at University of Oxford in England found a 12% overall reduction in total cholesterol in patients taking 600-900 mg garlic daily vs. those receiving placebo.3 In a German study, 261 patients were given either 800-mg garlic powder tablets or placebo. After 12 weeks, patients taking garlic experienced a 12% and 17% decrease in serum cholesterol and triglyceride levels, respectively, compared with those taking the placebo.4

The American Heart Association (AHA) states that there is clear evidence to support garlic’s potential for “reducing the risk of atherosclerosis.”5 The association also points to a meta-analysis showing that half a clove per day lowers serum cholesterol by approximately 9%.

The Agency for Healthcare Research and Quality conducted a meta-analysis of 70 randomized controlled trials that reviewed garlic and its effects on CV factors and outcomes.6 All trials lasted at least four weeks. Of the trials, 37 showed small but statistically significant reductions in total cholesterol at one month (range: 1.7-17.3 mg/dL) and three months (12.4-25.4).6 Reductions were also seen in LDL and triglycerides.6 It is unclear if these results are sustainable beyond three months. Data are insufficient to draw any conclusions on garlic’s effect on claudication and MI.

Mechanism of action

The Allium family includes naturally occurring sulfur-containing compounds. Alliin, the primary chemical ingredient of garlic, is structurally similar to cysteine, an amino acid containing sulfur.7 Though garlic contains a number of active compounds, the ones felt to be most responsible for therapeutic action are diallyl disulfide and its mono S oxide (allicim).5 Theory holds that this chemical may promote hypocholesterolemia by inhibiting cholesterol synthesis.5 The mechanism of the mild platelet aggregation inhibition is not clear but may be due to the significant antioxidant action of garlic.

Side effects

The main concern of most patients is the herb’s strong odor, which is not only notable on the breath of anyone consuming garlic but in their perspiration as well. “Deodorized” supplements are available, but their efficacy is considered to be reduced.1 Consistent use of oral supplements can cause GI irritation, nausea, diarrhea, diaphoresis, bleeding disorders, and allergic reaction.2 Garlic supplementation should be discontinued one to two weeks before any surgery. It should not be used in children or in pregnant or lactating women.2 Large quantities may cause anemia.

Drug interactions

Patients on anticoagulant therapy (warfarin, clopidogrel [Plavix], aspirin) should not use garlic supplementation because of possible potentiation of the anticoagulation and subsequent bleeding disorders. There is some concern that the effectiveness of oral contraceptives might be inhibited, so concomitant use with garlic is not recommended. Finally, concomitant garlic consumption has been shown to decrease serum concentrations of cyclosporine and saquinavir.2

Dosage

Garlic is commonly consumed in capsule form. The recommended dose with meals is 1-3 g of 1.3% alliin per day.2 This is equivalent to one-half to one clove of fresh garlic. Enteric-coated formulations are available to help reduce GI irritation.

Cost

Cost depends largely on the formulation but typically ranges between $8 and $12 per month for capsules. Supplements are widely available.

Summary

Garlic is a safe, mildly effective therapy for dyslipidemia. Small but significant LDL and triglyceride reductions can be expected. However, in light of the ever-growing list of benefits gleaned from the “statin” family of anticholesterol drugs, garlic should not be relied on as the sole method of cholesterol and atherosclerotic control. It is appropriate for adjunct lipid control.

References

1. Herb Society of America. Garlic: An Herb Society of America guide. Medicinal uses and ethnobotany. Available at www.herbsociety/org/garlic/gmeduse.php. Accessed July 10, 2006.

2. Dvorkin L. Introduction to herbal supplements for pharmacists and other health care professionals. Available at www.mcphs.edu/rc/ccap/herbs/garlic_properties.htm. Accessed July 10, 2006.

3. Silagy CS, Neil A. Garlic as a lipid-lowering agent: a meta-analysis. J Roy Coll Physicians Lond. 1994;28:39-45.

4. Garlic and cholesterol. Available at www.garlic.mistral.co.uk /cholest.htm. Accessed July 10, 2006.

5. Howard BV, Kritchevsky D. Phytochemicals and cardiovascular disease. A statement for healthcare professionals from the American Heart Association. Circulation. 1997;95:2591-2593.

6. Agency for Healthcare Research and Quality. Garlic: Effects on Cardiovascular Risks and Disease, Protective Effects Against Cancer, and Clinical Adverse Effects. AHRQ Publication No. 01-E022, October 2000. Available at www.ahrq.gov/clinic/epcsums/garlicsum.htm. Accessed July 10, 2006.

7. Garlic. Available at www.naturalherbsguide.com/garlic.html. Accessed July 10, 2006.