Ginkgo biloba is one of the oldest living tree species known. Alsocalled ‘‘maidenhair tree,” “Kew tree,” “fossil tree,” and “Japanese silver apricot,” ginkgo is unique, with no known close living relatives. Often misspelled “gingko,” this tree is native to China but has been successfully cultivated in other parts of the world.1
Ginkgos are medium-sized deciduous trees, usually growing to 70-110 feet in height and possessing an angular crown and long erratic branches. The characteristic fan-shaped leaves turn bright yellow in the fall. Some ginkgo trees have beenestimated to reach 2,500-3,000 years of age; this longevity is attributed to their inherent disease resistance and ability to form prodigious roots and sprouts.2
Background
Ginkgo biloba has been used in China for medicinal purposes for thousands of years. In recent times, ginkgo has been intensely studied for the treatment of vascular diseases and memory enhancement, particularly in Alzheimer’s dementia.3 One of the 10 best-selling herbal supplements in America, ginkgo has been the subject of more than 120 published clinical trials, mostly conducted in Europe. In a 2003 review article, a source claimed that during the previous 20 years, more than 2 billion daily doses of ginkgo had been sold in the United States alone.4
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Alzheimer’s and other types of vascular dementia are some of the most baffling and costly health problems clinicians face, and the aging of the baby-boom generation greatly increases its burden on the rest of society. The current annual price tag of Alzheimer’s is already well over $60 billion.5 With good reason, health-care consumers eagerly gravitate to any and all methods that offer the potential to delay or possibly prevent these conditions, and ginkgo resides at the top of the list of attractive options.
Technical information
Ginkgo contains two types of chemicals believed to be active. The flavonoids and terpenoids are thought to function as neuroprotective agents, antioxidants, free-radical scavengers, membrane stabilizers, and platelet-activating factor inhibitors.
These benefits, along with certain key inhibitory actions of age-related loss of muscarinergic cholinoceptors and the simultaneous stimulation of choline uptake in the hippocampus of the brain, are possible keys to ginkgo’s efficacy in memory enhancement. The effect of ginkgo is not immediate but rather accumulates over a period of at least 6-12 weeks.1
In addition to these chemoprotective mechanisms, ginkgo also improves capillary-level arterial blood flow by promoting endothelium relaxation factor.4 This quality is being studied in such conditions as peripheral vascular disease and intermittent claudication.
A meta-analysis of 33 trials showed ginkgo biloba to be safe and offered promising evidence for memory enhancement and cognition improvement in trial participants. These trials all earned an evidence level grade of “A.” Most striking was a meta-analysis of 50 articles examining the effect of ginkgo, specifically on cognitive measures in diagnosed Alzheimer’s patients. In four of these trials with a total of 212 patients, a significant positive effect noted in the ginkgo group equaled that of the prescription drug donepezil (Aricept).4
These trials, which were also given an “A” rating, used the efficacy measure of the Alzheimer’s Disease Assessment Scale-Cognitive Subscale as a standardization of outcomes.
Currently, the National Center for Complementary and Alternative Medicine (NCCAM), a division of NIH, is conducting a large clinical trial exploring ginkgo’s potential in preventing the onset or progression of Alzheimer’s dementia. This multicenter randomized clinical trial is slated to end in July 2009.6
Safety, drug interactions, and contraindications
As with use of any plant product, contact dermatitis and other atopic reactions are always possible. Persons with known allergic histories should spot-test ginkgo on skin or try a small oral test dose to watch for reaction before continuing. The most commonly listed side effects are usually mild and include nausea, diarrhea, flatulence, and vomiting. Ginkgo seeds are not the medicinal part of the tree and should never be consumed raw because of toxicity, even though in parts of China, cooked or processed seeds are eaten without adverse reactions.7
Because of ginkgo’s inhibitory action on platelet-activating factor, there is a mild potentiation of any anticoagulation, so concomitant use with warfarin or other blood-thinning agents should be monitored.4
Dose, how supplied
Internationally, the standardized form of ginkgo is known as EGb 761. In the United States, since numerous formulations and brands are available, the standard is for the product to contain 24% ginkgo flavonoids, 6% terpene lactones, and no more than five parts per million of ginkgolic acids.4 Ginkgo leaf extract is primarily available in capsule form, and recommended amounts range from 120-240 mg per day in two or three divided doses. It is also available in dried leaf form for making tea.
Cost
Depending on the brand and source, a typical month’s supply of ginkgo will cost between $15 and $20.
Summary
In light of its comparatively mild side effects and promising efficacy, ginkgo biloba appears to be a safe additive to any clinician’s arsenal in the fight against age-related dementias and vascular diseases. It is reasonable in cost, readily available, and shows very little drug-drug interaction with prescription medications. The health-care community awaits the publication of the NCCAM trial data to provide more information on this interesting neutraceutical.
References
1. Skidmore RL. Mosby’s Handbook of Herbs & Natural Supplements. 3rd ed. St. Louis, Mo.: Elsevier Mosby; 2006:488.
2. Wikipedia. Ginkgo. Available at http://en.wikipedia.org/wiki. Accessed August 1, 2007.
3. University of Maryland Medical Center. Ginkgo biloba. Available at www.umm.edu/altmed/articles. Accessed August 2, 2007.
4. Sierpina VS, Wollschlaeger B, Blumenthal M. Ginkgo biloba. Am Fam Physician. 2003;68:923-926. Available at www.aafp.org/afp/20030901. Accessed August 2, 2007.
5. Cummings JL, Frank JC, Cherry D, et al. Guidelines for managing Alzheimer’s disease: part I. Assessment. Am Fam Physician. 2002;65:2263-2272. Available at www.aafp.org/afp/20020601. Accessed August 2, 2007.
6. National Center for Complementary and Alternative Medicine. Ginkgo. Available at http://nccam.nih.gov/health. Accessed August 2, 2007.
7. Fetrow CW, Avila JR. Professional’s Handbook of Complementary & Alternative Medicines. Springhouse, Pa.: Springhouse Corp; 1999:279.
