Garlic has a long history of use as a medicine. As early as the Middle Ages and as late as World War II, garlic was used to fight infection. Within the last few decades, scientists have taken a close look at the medicinal potential of garlic, especially its possible effect on heart health. A recent article in Nutrition in Clinical Care summarized what scientists know about the potential heart-protecting benefits of garlic.

Some research has shown that garlic significantly lowers blood lipids--total cholesterol, LDL cholesterol, and triglycerides--without lowering "good" HDL cholesterol. The mechanism by which this may occur is not clear. One possibility is that it affects how much cholesterol is produced by the liver. Garlic may also act as a blood thinner, reducing the risk of clots that could lead to a stroke or heart attack, and several studies have demonstrated a modest decrease in blood pressure in people who consume garlic. Scientists are also studying garlic's ability to lower homocysteine levels (elevated homocysteine is associated with an increased risk of heart disease).

In spite of some promising research on the health benefits of garlic, though, there are still many unanswered questions. A clear pattern between doses, forms, and effects has yet to emerge. Must garlic be used fresh, or are garlic supplements just as good? The amounts of garlic--in the form of fresh, powder, or extract--used in research studies varies, from one clove to the equivalent of 28 cloves a day. Cooked or raw? Pressed or whole? Some studies have shown that cooking reduces its ability to lower cholesterol. Other research suggests that crushing or cutting the cloves is necessary to activate allium, the compound that appears to be responsible for its heart health benefits.

What's the bottom line? Research in this area continues, but there is still much that scientists don't know about the relationship between garlic intake and heart health. So if you enjoy garlic, use it, but it is still too early to assume that "a clove a day" will keep heart disease away.

Source

Garlic and cardiovascular disease.
MH. Loy,  et al., Nutrition in Clinical Care, 2000, vol. 3, pp. 145--152