August 17, 2005
How Garlic Works Its Cardiovascular Magic
Study uncovers mechanism by which the herb does some damage to do some benefit
The way in which garlic inflicts gastric pain may also be the way it confers cardiovascular benefits, a new study suggests.
The finding, reported in this week's issue of the Proceedings of the National Academy of Sciences is preliminary, however, and far from convincing for some experts.
"It's a possible mechanism for cardiovascular benefit from garlic, but they're a long way off from tying the two together," said Joe Vinson, a professor of chemistry at the University of Scranton in Pennsylvania. "They didn't do anything that convinced me that they've discovered the mechanism."
"It's still in the realm of very basic research," added Ruth Kava, director of nutrition at the American Council on Science and Health in New York City. "Whether or not it's going to have any real impact in terms of human health, it's much too early to say."
If the study is confirmed and replicated by other researchers, however, "it may provide a role for future pharmaceuticals," Kava added.
Garlic, along with onion, leek, chives and shallots, belongs to the plant genus Allium, and is known for its pungency and spiciness.
According to the study, these plants have been used for centuries to treat hypertension, high cholesterol and blood clots.
Garlic, in particular, has been tentatively linked to a variety of beneficial health effects, from reducing blood pressure and cholesterol to treating cancer.
"Garlic lowers your blood pressure, sometimes lowers your cholesterol, sometimes relaxes your arteries," Vinson said. "I say sometimes because not every study showed this."
But garlic has darker side effects, namely skin irritation and swelling of the legs.
Study co-author David Julius, a professor of cellular and molecular pharmacology at the University of California, San Francisco, has been interested in this darker side, studying how plants produce pain as a way to figure out how our sensory neurons detect painful stimuli.
For example, capsaicin in chili peppers causes an intense burning pain by activating specific neurons. Julius has discovered that capsaicin acts specifically on a cellular ion channel belonging to the TRP channel family.
Once activated, this channel lets sodium and calcium ions enter cells. This sends distress messages to the spinal cord, and then on to the pain centers of the brain.
Wasabi and mustard oil work in a similar way, generating pain and inflammation via TRPA1, another member of the TRP family.
"It's kind of a shared molecular mechanism where plants have developed all these interesting and, in some cases, potent defenses that probably serve a plant well because they act as anti-predatory mechanisms to tell squirrels and rats and other organisms that haven't learned how to cook with these to 'stay away, you don't want to eat this,'" Julius explained.
And garlic apparently works the same way.
In this study, Julius and his co-authors showed that a molecule in garlic called allicin stimulated sensory pain neurons in rats by activating the TRPA1 channel.
"Allicin was already known to be the main pungent ingredient in garlic," Julius said. "Consistent with this, we showed that allicin is, indeed, an activator of TRPA1."
The neurons released neurotransmitters in the spinal cord to generate pain signals, and released neuropeptides at the site of sensory nerve activation (meaning the skin, lips etc.), which resulted in vasodilation -- a healthy enlargement of blood vessels -- as well as inflammation.
These were test tube experiments only, however, and the work needs to be replicated in animals and humans.
"This is possible good news about garlic, but it's not related directly to the heart," Vinson said. "It's not getting me convinced that I should be taking garlic personally."
For more on garlic and health, visit Garlic Central (www.garlic-central.com ).