One of the most popular herbs on the market, ginkgo biloba has been prescribed for centuries in Asia as a means of treating dementia and improving memory and concentration.
Researchers from the Oregon Health Sciences University may have found another use for ginkgo: reducing the amount of brain damage caused by a stroke.
"Here we have an agent that's been available for more than 2,000 years that has some of the same effects as drugs being designed to limit free radical damage or act as an anti-platelet agent," said Dr. Wayne Clark, whose research was presented at American Academy of Neurology's recent meeting in San Diego. Clark added that ginkgo "seems to provide protection" for cells that have been damaged by stroke.
Strokes are the third leading cause of death in the United States, killing an estimated 160,000 Americans annually. A stroke occurs when blood flow to the brain is disrupted, killing brain cells by robbing them of oxygen and other nutrients. They are usually caused by the blockage of a blood vessel to the brain, or a ruptured blood vessel that causes bleeding into the brain.
Depending on the portion of the brain that is damaged, stroke victims can suffer a variety of disabilities, including paralysis, slurred speech, memory loss and confusion. Experts believe that of the 570,000 Americans who survive a stroke each year, up to 18% will have another stroke within a year.
In the study, Clark and a team of investigators from the Oregon Stroke Center divided 60 adult mice into three groups. The first group received 50 milligrams of a regulated ginkgo preparation from Germany orally every day for seven days. The second group of mice received 100 milligrams of the same preparation for the same duration. The third group was administered a placebo.
On the seventh day, the scientists artificially induced strokes in the mice with a silicone-coated filament. A day later, they measured the level of neurologic function in each group. They also measured the percentage of damage in each brain hemisphere and the infarct volume (the area of cell damage resulting from stroke) in each brain.
Mice that received the smaller dose of the ginkgo preparation were shown to have a much lower average infarct volume (13 cubic millimeters) compared to the high-dose group (22 cubic millimeters) and the placebo group (20 millimeters). The average percentage of hemisphere damage was also considerably lower in the low-dose group (14%) versus the high-dose and placebo groups (21% and 20%, respectively). In addition, mice fed the lower dose of ginkgo had slightly higher neurological function scores than those that received either the higher dose or placebo.
The authors of the study added that ginkgo may provide additional benefits to people after suffering a stroke. Because it is an antioxidant, ginkgo would play an important role in the neutralizing of free radicals, destructive molecules that damage cells and are caused by injuries to the body -- including stroke.
"Ginkgo seems to provide protection to cells in the brains that have been damaged by the free radicals released during a stroke," said Clark. "In addition to reducing stroke injury, ginkgo may also be useful in improving memory following a stroke."
One important side-effect was noted in the mice that received the higher dose of the ginkgo preparation, however. Ten percent of the mice in that group showed significant intracerebral hemorrhaging within the damaged areas of the brain; no such condition was seen in the low-dose or placebo groups.
Clark speculated that the hemorrhaging might be due to ginkgo's natural properties. "The higher dose, since we know gingko has this anti-platelet effect, may have increased bleeding in their brains," he said.
Mouse Study Does Not a Human Stroke Cure Make
While a low dose of ginkgo was shown to offer some protection against stroke damage, a larger dose had no beneficial effect and, in some cases, appeared to increase the risk of bleeding in certain subjects. Based on that risk, the researchers warned against the use of the supplement in humans at risk for stroke until more thorough studies have been conducted.
"More work is needed to determine the proper dose," said Clark. "In addition, because ginkgo is also a mild blood thinner, it may be risky to use it in patients on blood thinning medications commonly prescribed in people at risk for stroke."
The scientists also noted that the type of ginkgo preparation used in the study was produced in Germany, a country in which supplements are regulated and manufactured to extremely high standards. In countries whose standards are not as high, ginkgo supplements could be made that do not have consistent amounts of antioxidants, blood-thinning compounds and other substances, and thus may not produce the same effects in patients.
Nevertheless, many health experts viewed the Clark study as an important step forward, not only in finding a way to limit the effects of stroke, but in validating the therapeutic qualities of ginkgo biloba.
"I'm happy that Clark has found this, and it certainly bears more investigation," said Dr. Marilyn Rymer, medical director of The Stroke Center at St. Luke's Hospital in Kansas City, Missouri.
"Think about what happens in a stroke," added Charles Fetrow, a clinical pharmacist at St. Francis Medical Center in Pittsburgh. "You get a blood clot lodging in the vessels of the brain. Animal studies have shown that ginkgo enhances blood flow to tissues, and while we are not sure of the mechanism, we know that ginkgo either dilates the blood vessels or changes the blood to make it more slippery.
"I wouldn't suggest everyone run off and buy ginkgo," said Fetrow, "because you have to be careful about extrapolating from mice to humans. But the study looks very interesting."