Q: Why is garlic used to treat cold or fever? A: Garlic ( Allium sativum L.), a member of the onion genus, is known only from cultivation (that is, it does not grow wild). In addition to its culinary virtues, it has been used for millennia to treat infections and to benefit the arteries (in modern terms, to reduce blood pressure and cholesterol). The use of garlic to treat respiratory symptoms was mentioned nearly 2000 years ago by the Greek physician Dioscorides. In later European tradition, even tying garlic around the neck was believed to ward off illness.
When raw garlic is crushed, an enzymatic reaction transforms the sulfur-containing compound alliin into allicin, an unstable compound that is responsible for the odor of fresh garlic. Allicin has been shown to have antiviral, antibacterial, antifungal, and antiprotozoal activity. However, it is not the only active ingredient: others of the over 30 sulfur compounds found in garlic products have similar activities. The beneficial effects of these compounds probably motivated garlic's use to treat respiratory infections, including pneumonia and tuberculosis, as well as colds and flu.
Many placebo-controlled clinical trials of garlic have explored its cardiovascular benefits, but only one has studied its use for colds. That study found that subjects who took garlic daily over three winter months had less than half as many colds as subjects who took placebos. Garlic users also recovered much faster from their colds (on average 1.5 days of symptoms versus 5 days for the nonusers). No single study can be conclusive, but the scientific evidence to date clearly favors garlic's traditional use to treat colds.
Both cooking and stomach acid destroy alliinase, the enzyme that makes allicin, so garlic is most potent when minced, allowed to sit for several minutes, then eaten raw. Consumption of 2 to 4 grams (one to two cloves) three times daily has been recommended for treatment of acute illnesses. However, many people find raw garlic to be irritating and unpleasant. A more palatable alternative may be an equivalent dosage of a dietary supplement that supplies allicin. Enteric-coated supplements, which dissolve after they have passed through the stomach, preserve potency and minimize "garlic breath."
Related Websites: Garlic Central
References: Dioscorides et al., Dioscorides: De Materia Medica—English, IBIDIS, Johannesburg, 2000; E/S/C/O/P Monographs: The Scientific Foundation for Herbal Medicinal Products, 2d. ed., ESCOP, Exeter, and Thieme, Stuttgart and New York, 2003; J.C. Harris et al., Antimicrobial properties of Allium sativum (garlic), Appl. Microbiol. Biotechnol. 57:282-286, 2001; P. Josling, Preventing the common cold with a garlic supplement: A double-blind, placebo-controlled survey, Advances Ther., 18:189-193, 2001; Y. Tsai et al., Antiviral properties of garlic: in vitro effects on influenza B, Herpes simplex and Coxsackie viruses, Planta Medica, 51:460-461, 1985. Wendy L. Applequist, Ph.D. Assistant Curator William L. Brown Center for Plant Genetic Resources Missouri Botanical Garden