A member of the lily family, garlic has been prized for its healing properties since at least 2600 b.c. Anthropologists have found prescriptions for the herb chiseled onto ancient Sumerian clay tablets. Cultures around the world have embraced garlic as a cure for everything from colds to cancer. Prior to the discovery of penicillin, garlic was the treatment of choice for infections, such as pneumonia, bronchitis, tuberculosis and dysentery.
Scientists believe that it is the same sulfur compounds that imbue garlic with its characteristic odor and flavor that are responsible for the herb’s health benefits. Most of the research has focused on the sulfur compound allicin, which has antimicrobial properties. Allicin is created when alliin, a sulfur-containing amino acid in garlic, comes into contact with another garlic compound, the enzyme allinase. This enzymatic reaction takes place when garlic is chopped, crushed or chewed, but it is destroyed during cooking.
A 2001 clinical trial supports the use of garlic for preventing and treating colds. In the study, researchers randomly assigned 146 volunteers to two groups. One group received a garlic supplement containing allicin. The other group was given a placebo. Over a 12-week period between November and February, the volunteers kept a daily diary in which they recorded cold symptoms. At the end of the study, researchers found that the group given the garlic supplement reported that only 24 participants had colds, in contrast to the placebo group, in which 65 participants suffered from colds. The researchers also discovered that the study participants taking garlic who did get sick recovered more quickly.
Because raw garlic can cause gastrointestinal upset if taken on an empty stomach, it’s best to consume it with meals. If you’re adding garlic to a cooked dish, such as pasta or soup, add it at the end of cooking to prevent destruction of the antimicrobial compounds.
If you’re taking prescription anticoagulant drugs, consult your doctor before taking large amounts of garlic because of the herb’s blood-thinning properties. For the same reason, discontinue garlic supplements seven to 10 days before surgery, and tell doctors you are taking garlic before any unplanned medical procedure.
A great deal of controversy exists over the best form of garlic and the proper dosage. According to the Herb Research Foundation, a typical dosage of garlic is 600 to 900 mg a day of powdered garlic in capsules or tablets (standardized for alliin content), 4 ml a day of aged garlic liquid extract, 10 mg a day of garlic oil capsules, or one medium-sized clove of fresh garlic.