The sulfur compound allicin, produced by crushing or chewing fresh garlic or by taking powdered garlic products with allicin potential, in turn produces other sulfur compounds: ajoene, allyl sulfides, and vinyldithiins.68 Aged garlic products lack allicin, but may have activity due to the presence of S-allylcysteine.
Many publications have shown that garlic supports the cardiovascular system. While earlier trials suggest it may mildly lower cholesterol and triglyceride levels in the blood,69, 70, 71 more recent trials found garlic to have minimal success in lowering cholesterol and triglycerides.72, 73, 74 Garlic also inhibits platelet stickiness (aggregation) and increases fibrinolysis,75 which results in a slowing of blood coagulation. It is mildly antihypertensive76 and has antioxidant activity.77
Garlic's cardiovascular protective effects were illustrated in a four-year clinical trial on people 50-80 years old with atherosclerosis.78 It was found that consumption of 900 mg of a standardized garlic supplement reduced arterial plaque formation by 5-18%. The benefits were most notable in women.
In test tube studies garlic has been found to have antibacterial, antiviral, and antifungal activity.79 However, these actions are less clear in humans and do not suggest that garlic is a substitute for antibiotics or antifungal medications.
Human population studies suggest that eating garlic regularly reduces the risk of esophageal, stomach, and colon cancer.80, 81 This may be partly due to garlic's ability to reduce the formation of carcinogenic compounds.