Garlic Tales

Scientists are continuously trying to unvail  the secrets of the garlic, to zero in on what makes the herb so beneficial.

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A herb that is a part of almost every Indian kitchen continues to make news. Garlic, or Allium sativum, one of the oldest medicinal herbs known to human beings, is now in laboratories, while scientists look at what makes it so beneficial.

Indeed, garlic seems to possess near-magical health properties. Yet science has not found it an easy herb to understand. Despite tall claims from practitioners of alternative medicine, no one clearly knows how good garlic is and why it is considered to be so beneficial. But now scientists are rapidly unravelling its secrets.

Over the years, people with varying backgrounds have claimed that the bulb is good for controlling blood pressure and reducing cholesterol. It is supposed to have anti-inflammatory, antimicrobial, antiviral, antioxidant and anticoagulant properties, apart from a few other benefits. There is now good evidence that most of these claims are true. And scientists have recently discovered new properties as well: it can reduce blood sugar levels, and is thus good for controlling diabetes. Yet conventional wisdom is not always right: it may not, after all, reduce cholesterol.

While evidence on the utility mounts, scientists are also beginning to understand why. For example, garlic’s antioxidant properties have been a mystery to scientists. It has been known to be a powerful antioxidant (a compound that destroys damaging free radicals); in fact a bit too powerful for comfort. It has a compound called allicin that is an antioxidant, but its structure could not explain its power. Till now, that is.

Derek Pratt, professor of chemistry at Queen’s University in Canada, has found out why garlic is so powerful.

A compound akin to allicin is found in other plants of the family alliaceae — such as shallots, onions and leeks. However, none of these plants has garlic’s beneficial powers. This is because the allicin found in garlic breaks down into another compound called sulphenic acid, which rapidly cleans up free radicals in its path. Without this breakdown, allicin cannot be so effective an antioxidant.

“This compound is the most powerful antioxidant known to us,” says Pratt, who published his results last week in the journal Angewandte Chemie.

While its efficacy in dealing with free radicals is now beyond doubt, garlic is probably not so effective in reducing bad cholesterol, the Low Density Lipoproteins (LDL). Several studies on its effect on blood cholesterol led to conflicting results, but one in Stanford University more than a year ago was probably the most conclusive. This six-month-long study found no correlation between consumption of garlic and reduction of LDL. “We are convinced now that garlic does not reduce bad cholesterol,” Christopher Gardner, the Stanford professor who led the research, had told Knowhow soon after publishing the results of the study.

But that does not mean it is not useful in treating high cholesterol. Its antioxidant properties are useful in treating cardiovascular diseases in general, and even for treating high cholesterol. This is because garlic suppresses the oxidation of LDL in the blood. LDL is called bad cholesterol because it sticks to the artery walls and clogs the arteries. However, it is not LDL that actually does the damage but oxidised LDL. Several studies have shown that garlic suppresses oxidation of LDL and thus prevents the formation of plaques in the arteries. It makes bad cholesterol not so bad.

“Garlic does reduce LDL oxidation,” stresses Khalid Rahman, reader in the physiological biochemistry at Liverpool University in the UK, who has conducted several lab and clinical studies on the herb.

There is increasing evidence that it can lower blood pressure, particularly when BP is elevated only mildly. A recent meta-analysis (analysis of all published literature) by scientists at the University of Adelaide showed that it does lower blood pressure. However, the scientists also warn that the evidence is not strong enough to use garlic as the only means of therapy.

These results are from clinical studies, which mean that they have been done on people. The results are equally encouraging in pre-clinical studies done in the laboratory. There, the herb has been shown to be anti-inflammatory and anticoagulant. It may be able to help dissolve clots and improve blood circulation. A few months ago, Japanese scientists (at the RIKEN and other institutions) showed that it could lower blood glucose levels in rats.

The list of beneficial properties is actually lengthening every day, but the topic is not without its controversy either.

This is because there are some studies showing that garlic had no effect on lowering blood pressure or reducing cholesterol, while some others showed that it did do so. This variability, fortunately, is not hard to explain. Scientists explain this contradiction through differences in the duration of the trials, and also on the variability in the properties of garlic. “The factors influencing a clinical study with garlic are difficult to control,” says Pratt.

Although we know that it is beneficial, not all kinds of garlic may act in the same manner. “In my view there is a group of people who are non-responders to garlic, like to any other medication,” says Rahman.

However, garlic has caught the attention of hundreds of scientists throughout the world. We will learn more about this wonder herb in the coming years.

Sources: The Telegraph (Kolkata, India)

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