Alternative medicine has been touting the health benefits of garlic for centuries, from its anti-bacterial and antifungal properties, to its positive effects on the cardiovascular system.

Now, U.S. researchers say they have figured out precisely why the pungent clove makes such a valuable health tonic: it boosts the body's own production of a compound that relaxes blood vessels, increases blood flow and prevents blood clots and oxidative damage.

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"This will help us standardize over the-counter garlic supplements, and ensure they have the ingredients that produce the key compound,'' said David Kraus, a physiologist in the department of environmental health sciences at the University of Alabama in Birmingham.

Much of the research into the pharmacological benefits of garlic has focused on the organic polysulphides that the clove is rich in, the best known of which is Allicin.

But the new research suggests Allicin and similar biologically active compounds are only a piece of the puzzle, and that it's the chemical messenger that is produced when these compounds are metabolized that is important.