Ginkgo Extract Appears to Slow Alzheimer’s
Scientists may now have one more weapon in their continuing war against Alzheimer’s disease, an herbal medicine called ginkgo biloba, researchers said Tuesday.
Vitamin E, ibuprofen, estrogen and the anti-Parkinson’s drug selegiline have all been shown recently to slow the progression of this devastating disease, which affects more than 4 million Americans.
Now, scientists from the New York Institute for Medical Research report that an extract of ginkgo biloba commonly available in health food stores may be as effective as any of those.
They found that 27% of patients who took the herbal extract for six months or longer showed improvements in mental functioning--including reasoning, memory and ability to learn--compared to only 14% of those who took a placebo. The results were “modest,” in the words of study author Dr. Pierre L. LeBars, and the team has no idea which of the many chemicals present in the extract were responsible for the effect.
The team’s results are published today in the Journal of the American Medical Assn.
Although the study was paid for by the drug’s manufacturer, it reflects the growing interest among some scientists in so-called alternative medicine, which makes greater use of natural products rather than synthetic drugs. Some researchers question the use of such natural products because their composition varies from lot to lot and the complex mixture of components makes it difficult to determine which constituents are effective.
Zaven Khachaturian, research director for the Alzheimer’s Assn., cautioned that Alzheimer’s patients should not rush to medicate themselves with the drug.
“What’s exciting is, it seems to be fairly safe and gives us a new vista to explore” for drugs that will be even more active, he said. “[But] the results are no better than those with some of the other compounds.”
Khachaturian and others also noted that ginkgo extract acts as a blood thinner and could be unsafe for patients who are already taking anticoagulants or other blood-thinning agents. Other potential side effects include nausea, diarrhea and flatulence.
Ginkgo is extracted from the bark, nuts and leaves of the Ginkgo biloba or maidenhair tree, which grows mainly in temperate climates. It is a complex mixture of as many as 300 chemicals that has been used medicinally for more than 5,000 years because of its antioxidant and anti-inflammatory properties and a perceived ability to increase blood flow.
Among the many uses claimed for it by proponents are the treatment of arthritis, asthma, bronchitis, depression and heart disease. Few of these uses have been studied in clinical trials, however, and they are not widely accepted in the medical community.
Psychopharmacologist Dr. Alan J. Cohen of UC San Francisco, however, says he has has demonstrated that it enhances sexual function in patients taking antidepressant drugs. Patients who use it for that purpose also “routinely describe benefits in cognition,” the ability to think, he noted.
Khachaturian, for one, welcomes the new study. “It is very significant that readily available substances may turn out to be effective treatments for Alzheimer’s,” he said. “This may speed the development of treatments, plus reduce the cost, compared with developing new drugs from scratch.”
Dr. Leon J. Thal of UC San Diego said: “We’re not worried about whether or not this is a herbal compound, but about whether it works.” He added: “These results are suggestive, but they are certainly not conclusive.”
Commercial ginkgo preparations can have vastly different compositions, depending upon the technique used to extract active ingredients from leaves and fruit.
The particular form studied in the new report is called EGb 761. It is widely used in Europe for the treatment of cognitive disorders and has been approved by the German equivalent of the U.S. Food and Drug Administration for the treatment of dementia, the impairment of thought processes characteristic of Alzheimer’s. EGb 761 is not generally available in the United States, although many other formulations are.
LeBars and his colleagues initially recruited 309 patients for their study--most with Alzheimer’s, but about 50 with dementia caused by strokes. More than a third dropped out, however, an unusually high number for such a clinical trial. Half the remaining patients received 120 milligrams of EGb 761 per day, while the other half received a placebo.
The mental abilities of the patients were assessed on two different objective scales at the beginning of the test and at regular intervals.
“Compared with the placebo group, the EGb group included twice as many patients whose cognitive performance improved and [only] half as many whose social functioning worsened,” LeBars told a news conference in Washington on Tuesday. “What is the mode of action? We really don’t know. . . . The study is the source of more questions than answers.”
LeBars also cautioned that the study was very small and that the volunteers were not followed for a long enough time to see if the effects persisted. But the results were sufficiently encouraging to justify larger trials, he noted.
In fact, Khachaturian said, a French company is already organizing such a trial to study larger doses and different dosing regimens and will include patients at an earlier stage of the disease.
Two drugs have been approved by the FDA for treating Alzheimer’s: Aricept (donezepil) and Cognex (tacrine), both of which provide some help to some patients. Several other newer drugs are being studied in ongoing clinical trials.
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Ginkgo Extract
Botanical name: Ginkgo biloba
Made from: Ginkgo trees
Reported medical benefits and uses: Relaxation of blood vessels, antioxidant, inhibits platelet aggregation, increases peripheral and cerebral blood flow, used as a cardiovascular tonic and as a brain tonic.
Background: Ginkgo biloba, at 300 million years, is one of the oldest living tree species. Individual trees can live more than 1,000 years. Extracts of the fruit and leaves of the ginkgo tree have been used in China for more than 5,000 years to treat lung ailments such as asthma and bronchitis, and as a remedy for cardiovascular diseases.
Side effects: Ginkgo biloba extracts are considered relatively safe and free of side effects, though taking very large doses may lead to diarrhea, nausea and vomiting, which can be controlled by reducing the amount consumed.
Other drugs that have shown promise for treatment of Alzheimer’s disease: ibuprofen, estrogen, vitamin E, selegiline (a Parkinson’s drug) and two drugs approved by the FDA, Aricept and Cognex (tacrine)
