3 May 2000
Ginkgo May Protect Brain Against Stroke Damage
by Kate Melville
Many drugs have been tried in an attempt to protect the brain from stroke damage, but all have been unsuccessful in humans. A new approach inspired by cancer and dementia research, is to try to limit the damage caused by destructive molecules called free radicals that follows a stroke. Antioxidants in ginkgo, compounds that counteract free radicals, make ginkgo an obvious candidate.
Researchers induced strokes in mice who had been receiving oral doses of ginkgo for one week. While a low dose appeared to offer protection against stroke -- reducing the area of the brain affected by 30 percent -- another, larger dose had no beneficial effect. This result prompted the researchers to warn that it is too early to recommend the use of gingko in humans at risk for stroke.
"More work is needed to determine the proper dose," said Wayne Clark, MD, director of the Oregon Stroke Center at Oregon Health Sciences University and lead author of the report. "In addition, because ginkgo is also a mild blood thinner, it may be risky to use it in patients already on blood thinning medications commonly prescribed in people at risk for stroke."
A stroke occurs when blood flow to brain tissues is disrupted, killing brain cells by robbing them of oxygen and nutrients. The most likely cause is blockage of an artery in the neck or head. When a portion of the brain is damaged, termed a focal infarction, patients are often left with some disability, such as paralysis, loss of speech or memory lapses.
Ginkgo has been used medicinally for centuries in Asia and in recent years has become one of the most prescribed medicines in Germany and France. The extract is derived from the nuts and large, fan-shaped leaves of the Ginkgo biloba, typically grown as a shade tree.
Ginkgo extract contains a number of pharmacologically active compounds. However, the relative concentrations of these can vary widely in the unregulated ginkgo sold in health food stores in the United States.
The researchers used a ginkgo preparation from Germany, where the extract is regulated and manufactured to have consistent concentrations of antioxidants, blood-thinning compounds and other compounds.
The authors add that some of these may bring along bonus benefits to people at risk for stroke. "In addition to reducing stroke injury, ginkgo may also be useful in improving memory following a stroke," Clark said.