Garlic is a key part of the Mediterranean diet and many cuisines around the world. But do supplements really lower cholesterol, fight cancer, reduce arthritis, and have other health benefits, as touted?
There have been thousands of studies on garlic, but its health effects remain something of a mystery. Garlic contains interesting compounds that have been linked to many proposed health benefits. One is allicin, a sulfur compound formed in raw garlic after a clove is cut or crushed. Allicin is a major source of garlic’s taste and smell. But not all scientists agree that allicin is the key ingredient, since it breaks down quickly into other compounds. And the enzyme that forms allicin can be destroyed if the whole clove is cooked before being cut (that’s why cooked cloves taste less garlicky). In fact, no one knows which, if any, component is most important.
Lab and animal studies suggest that garlic (or compounds from it) has a range of benefits. For example, it keeps blood platelets from sticking together, which reduces the risk of clots, and may have anti-cancer, anti-inflammatory, and cholesterol-lowering effects. But what happens in people is unclear. Nearly all human studies have been small, short, and/or poorly designed. Plus, they have used different garlic preparations and doses, making comparison difficult.
Garlic news:
• Cholesterol. While some studies have found that garlic reduces LDL (“bad”) cholesterol somewhat, others have shown little or no effect. A well-designed 2007 study from Stanford University found no benefit when it tested raw garlic and two popular supplements (one containing powdered garlic, the other an aged-garlic extract) for six months in people with high LDL. More recently, two analyses concluded that clinical trials have not shown consistent or significant improvements, while a 2012 review of 26 studies by Chinese researchers found garlic lowered triglycerides slightly (but not LDL cholesterol or other measures). Regardless of its effect on cholesterol, there’s no evidence that garlic prevents heart attacks (unlike statins).
• Blood pressure. Small, short-term studies have found that garlic can lower blood pressure slightly in people with hypertension. But various garlic preparations may have different effects.
• Cancer. The evidence is mixed, at best. Some (not all) population studies have found that people who eat a lot of garlic have a lower risk of certain cancers, notably stomach, colon, and prostate. But there have been few large, long-term randomized trials, which are needed to prove that it’s really garlic, and not something else about garlic eaters, that affects cancer risk. Two such studies, done in China a few years ago, reached opposite conclusions about the effect of garlic pills on the risk of stomach cancer.
• Other claims. For other conditions, such as upper respiratory infections, diabetes, and arthritis, there’s no good evidence of benefit.
Bottom line: There’s no harm in eating more garlic in your food if you like it and if it agrees with you (raw garlic may cause heartburn, stomach upset, bad breath, and body odor). But don’t take garlic supplements. Even if they do lower blood cholesterol or blood pressure or thin the blood, which is uncertain, the effect is small, so the supplements can’t replace medication. In any case, no one knows what form or dose would be best and they may interact with some medications.
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