28 Maret, 2009

Garlic & the Heart

Garlic has been used as a medicine for centuries. At first, garlic was used by physicians as a digestive aid. In more recent years, as researchers have isolated and studied individual compounds in garlic, the herb has been touted for its ability to lower cholesterol and blood pressure. Additionally, garlic is sometime promoted as an antibacterial, antiviral and anticancer herb.

Unfortunately, despite several decades of study on garlic and its components, the evidence remains mixed at best. In 2007, the results of one of the best-designed human studies to date were released. This study compared three formulations of garlic in a head-to-head test to see which, if any, was most effective at lowering cholesterol levels. Ultimately, researchers concluded that none of the garlic preparations were effective at lowering cholesterol.

However, these results are contradicted by earlier studies that show garlic can slightly lower cholesterol for the short-term and may have additional heart-healthy benefits, such as slowing the progression of coronary artery disease and perhaps slightly lowering blood pressure. In fact, the benefits of garlic, if any, remain a hotly debated topic, presumably driven by these conflicting study results.

Unfortunately for consumers, there is no scientific consensus on the value of garlic supplements, even while there may be ample anecdotal evidence or a strong tradition of herbal medicine. Fortunately, garlic does not appear to be harmful or have many side effects and can usually be added to the diet without causing hardship. However, it is important that anyone starting a supplementation program first clear it with their physician to make sure there is no risk of interactions with existing prescription drugs or other harmful side effects.

Known side effects of garlic include a pungent odor, upset stomach and possible allergic reactions. Garlic may also act as an anti-platelet and therefore should not be used immediately before surgery or in combination with existing anti-platelet drugs unless under the direct supervision of a physician. Finally, garlic may interact with certain antivirals that are used to treat HIV.

About garlic

Also known as the “stinking rose,” garlic is one of many plants in the allium family, which also includes chives, leeks, onions and scallions. Although grocery stores generally carry only one or two types of raw garlic, there are actually hundreds of sub-varieties that vary in size, shape, color, taste and other qualities. Garlic is also available as garlic powder and garlic salt, both of which are used in many recipes.

While garlic may be an important part of many culinary traditions, millions of people also take garlic preparations for their supposed health benefits. When garlic is pressed or crushed, an enzyme (which facilitates chemical reactions) called alliinase is activated. Alliinase helps to change the inactive compound alliin into the active compound allicin. Although allicin was once given the credit for garlic’s healthy effects, researchers now believe that allicin quickly changes as soon as it is exposed to oxygen in the air. Allicin combines with oxygen (oxidizes) to create new compounds, which results in over 75 active sulfur-containing substances such as S-allylcysteine and ajoene. The presence of these sulfur-containing substances earned garlic its classification as an organosulfur, and they now appear to be responsible for garlic’s health benefits, as well as its distinctive odor.

Traditionally, garlic has been used as a digestive aid and to fight infections. In more recent years, garlic has also been touted for its ability to lower cholesterol and high blood pressure, slow the advance of atherosclerosis, and prevent stomach and colon cancers. Medicinal garlic is usually sold in capsules or tablets that offer extracts of garlic. Some brands of garlic tablets are enteric coated, meaning they pass through the stomach for absorption by the small intestine to avoid any gastrointestinal discomfort.

Garlic's actual health benefits are the subject of wide-ranging research efforts. According to the National Center for Complementary Medicine, garlic may be able to slow the progression of atherosclerosis, and evidence is mixed on its ability to help lower high blood pressure. Garlic is most often mentioned for its ability lower cholesterol. However, in 2007, the results of one of the best-designed human studies to date on garlic and cholesterol were released. This study compared three formulations of garlic in a head-to-head test to see which, if any, was most effective at lowering cholesterol levels. Ultimately, researchers concluded that none of the garlic preparations were effective at lowering cholesterol.

Garlic is sometimes mentioned for its ability to reduce the risk of stomach and colon cancer, a claim that has not been validated by human trials.

Nevertheless, there remains an aggressive effort by supplement companies and some health experts to promote garlic as a healing herb. In many cases, pro-garlic advocates cite scientific studies, which may lead to a sense of confusion over garlic's health properties.

At least some of this confusion must be attributed to the problems with studying any herbal supplements, as well as a thorough understanding of the difference between lab studies and human studies. Supplements such as garlic are hard to study because it is hard to locate standardized extracts that are chemically identical, and because natural garlic contains many chemicals, it is difficult or impossible to know which chemicals may be causing any effect. Additionally, much of the research on garlic has been in lab studies, or studies in which scientists experiment on prepared solutions in test tubes, or animal studies. Garlic compounds that might be effective in the lab or animals may act differently once they are introduced into the human body.

It is unlikely these issues will be solved in the near future, at least in part because of the government's stance toward herbal and dietary supplements. These products are not under the control of the Food and Drug Administration, and while there are laws covering what supplement manufacturers are allowed to say in their advertising, there are no laws governing the purity, strength and production of garlic supplements. Unlike pharmaceutical products, so-called nutraceuticals are not required to undergo rigorous clinical testing in human beings to verify their health benefits. Fortunately, it appears there are few side effects to garlic supplements, so under the supervision of a physician, they can probably be safely added to most people's daily routine. The largest exception may be people who are taking anti-platelet drugs or who are scheduled for surgery, because garlic also has anti-platelet effects.

Potential benefits of garlic

The exact process by which garlic may be helping the body is not yet understood. Some of the substances found in garlic, such as sulfur-containing compounds, have been associated with specific health benefits and include the following:

* Adenosine. May help to prevent blood clots.

* Ajoene (Spanish for garlic). May help to prevent blood clots and lower cholesterol.

* Organic sulfide compounds (e.g., methyl allyl sulfide). May help to lower cholesterol and prevent cancer.

* Sulfur-containing amino acids (e.g., S–allylcysteine). May help to lower cholesterol.

Researchers continue to look for the specific sulfur–containing compounds that are responsible for reported health benefits.

In the context of heart health, garlic is often touted for the following benefits:

* Had similar effects to antioxidant vitamins (perhaps because it contains the antioxidants vitamin A, vitamin C and selenium). These effects included a reduction in plaque and prevention of further plaque buildup, which reduced the risk of atherosclerosis (hardening of the arteries).

* Improved circulation.

* Lowered blood pressure.

* Lowered levels of both cholesterol and blood fats (triglycerides), even when a very high-fat diet was consumed in short-term studies (1 to 3 months).

* Maintained elasticity (flexibility) of the major artery that pumps blood from the heart to the rest of the body (the aorta).

* Reduced the blood’s viscosity (stickiness), so it was less likely to clot.

While these results are impressive, they are contradicted by large analyses of previous studies, as well as at least one well-designed human study showing that there is insufficient data to draw any firm conclusions about garlic's effect on heart health. Most researchers agree that additional studies are necessary to determine if specific compounds in garlic can have beneficial health effects. Even though garlic may not significantly reduce cholesterol or blood pressure, it can be part of a healthy diet as it provides many heart-healthy antioxidants.

Preparation tips for garlic

Garlic appears to offer the greatest health benefits (if they exist) when it has been allowed to sit for 10 to 15 minutes after being pressed or crushed. During this time, sulfur-containing compounds are produced. Ideally, garlic is then consumed as a raw flavoring on food. Some experts even recommend that garlic cloves be chewed raw for maximum effect.

However, other experts warn that eating too much raw garlic can cause stomach upset or heartburn. Therefore, lightly cooking the garlic after it has sat for a while may be the best strategy. Too much heat should be avoided, because it can destroy one of garlic’s most important ingredients: allicin. This may help to explain why raw and cooked garlic have such different effects on health, and may explain why research results have been so different from one another.

Recommended daily amounts for garlic

The U.S. Food and Drug Administration (FDA) has not recommended a daily allowance of garlic, and people are encouraged to talk to their physician before taking any herbal supplements. Those who choose to take garlic supplements should be sure that the supplements are well coated (enteric coated), so that the garlic is not broken down within the stomach before it can pass into the small intestine and be absorbed. Also, herbal supplements should be taken only as prescribed. Experts generally recommend eating between 0.5 and 2 cloves of garlic per day. It should be noted that eating even small amounts of garlic often leads to both bad breath and body odor, as the sulfur is both breathed and sweated out of the body. Some people may also experience heartburn and/or gas.

Unless otherwise instructed by their physician, people should refrain from eating large amounts of garlic or taking garlic supplements if they:

* Are about to have surgery within the week

* Are breast-feeding

* Are pregnant

* Are children

* Have a bleeding or blood-clotting disorder

* Take blood clot-preventing medication (anticoagulant)

* Have an allergic reaction to garlic (which may include hives, swelling of the lips/tongue, trouble breathing or upset stomach)

* Have diabetes

* Take nonsteroidal anti-inflammatory drugs (NSAIDs), such as aspirin

* Take over-the-counter products such as antacids, ginkgo biloba, laxatives or supplements with high doses of vitamin C

In conclusion, garlic may have some benefits for heart health, as well as other medicinal properties. However, like all vitamin, mineral and herbal supplements, it should only be taken responsibly after talking with a physician.

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