Garlic (Allium sativum) originated in Central Asia, but is cultivated all over the world. The Bible mentions garlic, and garlic has been a common spice in Europe since the days of the Roman Empire.
Garlic contains sulphur compounds, the most important of which is allicin, which is created when garlic cloves are cut into or crushed. Allicin is deactivated within hours because it begins to react with garlic's other components as soon as the clove is crushed. Allicin's biological function is to repel herbivorous animals. But it also reacts with sulfhydryl groups in two groups of enzymes, cysteine proteinases and alcohol dehydrogenases, which typically play an important role in the metabolism of a wide variety of infectious organisms. The antifungal properties of garlic have long been used in folk medicine. (The fungi that cause Valley Fever are sensitive to garlic extracts.) Some evidence also suggests that allicin has anti-viral properties.
Sulfhydryl groups are also crucial components of some enzymes that participate in the synthesis of cholesterol. It has also been suggested allicin acts as an antioxidant. A review of the published and unpublished data from around the world reported that garlic produces a 12% reduction in total cholesterol after only 4 weeks of treatment (J Royal Coll Physicians 1994; 28:39). More research and large scale clinical studies will be necessary to establish what role allicin might play in preventing the development of heart disease.