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Ginkgo (Ginkgo biloba)

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by Steven Foster © 2009
Ginkgo

The best-selling phytomedicine on the European market is derived from the leaves of an ancient tree. The tree is ginkgo, Ginkgo biloba, a living fossil. Ginkgo is considered the oldest tree species to survive on earth, with a history dating back over 200 million years. Ginkgo species were once common in North America and Europe. Ginkgo biloba is the only surviving member of the ginkgo family. While its relatives became extinct in other parts of the world Ginkgo biloba survived in China, where it became known to Europeans in the eighteenth century, and subsequently was introduced as a ornamental tree throughout the Western world. Now ginkgo trees are found in virtually every city in the United States. It was first introduced to the U.S. in 1784. The common name Ginkgo is a phonetic pronunciation of a Japanese name for the tree. The species name "biloba" refers to the two distinct lobes, typical of the tree's leaves.

Ginkgos have survived over millions of years because of their genetic tenacity. They are long-lived trees, remarkably resistance to disease, pests, and fires. They also are extremely tolerant of air pollution, and are often planted in harsh city environments where most trees will not survive. The most common tree along Manhattan sidewalks is ginkgo. The trees will get to be over 100 feet tall. In Japan and China trees over a thousand years old are found at ancient temples. Its unique fan-shaped leaves with two lobes make it one of the easiest trees to identify once you become familiar with the unusual leaf shape.

Despite the fact that the tree occurs in China, the leaves are not one of the famous classical herbal drugs of ancient China. The first mention in Chinese herbals of use of the leaves comes relatively late. Ginkgo leaf is first mentioned in Lan Mao's Dian Nan Ben Cao (Pharmaceutical Natural History of Southern Yunnan), published in 1436 during the Ming dynasty. Lan Mao notes external use to treat skin and head sores as well as freckles. Internal use of the leaves is first noted in Liu Wen-Tai's Ben Cao Pin Hui Jing Yao (Essentials of the Pharmacopoeia Ranked According to Nature and Efficacy), an imperial commissioned work recorded in 1505. Liu Wen Tai notes use of the leaves in the treatment of diarrhea. The leaves of ginkgo are known in Chinese medicine as bai-guo-ye. Recent clinical reports in modern China suggest that the leaves lower serum cholesterol levels and have some clinical value in angina pectoris.

In Traditional Chinese Medicine the seeds (with fleshy rind removed) are considered more important than the leaves. The seeds are used as an astringent for the lung, to stop asthma, enuresis, and excessive leucorrhoea. It is thought to benefit ch'i (qi; vital energy), cough, and regulate urinary frequency. Studies have shown that the constituents ginkgoic acid and ginnol inhibit certain bacteria and fungal infections. In large doses the seeds are thought to have some toxic effect, perhaps leading to skin disorders or mucous membrane irritation.

Ginkgo leaves are a Chinese herb that has been used much more in the West than in its homeland. Over three hundred scientific studies on the chemistry, pharmacology and clinical effects of gingko leaf have been conducted by European researchers over the last 20 to 30 years. Unlike most herbs, ginkgo leaf extracts, rather than crude leaf material, are used for clinical purposes. The majority of studies on ginkgo leaf extract have involved a product produced by a German/French consortium, referred to in the scientific literature as EGb761. Ginkgo products are standardized to contain 24% of the bioflavonoids which occur in the leaf, as well as ginkgolides and bilobilides, a complex group of compounds found only in the ginkgo tree. Since virtually all research on ginkgo has involved high standardized extracts calibrated to specific quantities of chemical components, it is not possible to apply information from studies on the standardized extracts to ginkgo leaf itself.

The complex extract itself, rather than a single isolated component, is believed to be responsible for Ginkgo's biological activity. However, recently various research groups have focused on the effects of the ginkgolides themselves. They have been found to be very selective antagonists of platelet aggregation induced by platelet-activating factor (PAF), an inflammatory autocoid. Autocoids, synthesized in local tissue sites, mediate tissue response, such as pain perception, blood coagulation, and smooth muscle contraction. PAF is involved in various inflammatory, cardiovascular, and respiratory disorders. The ginkgolides have an anti-PAF action, helping to modulate various enzyme systems and ion pumps. The PAF antagonist effect of ginkgolides helps to explain ginkgo's broad-spectrum biological activity.

Most of the extracts available on the American market are made in Europe. Supplies are also coming from Japan, China, and elsewhere. Most of the ginkgo leaf used to manufacture European products is produced on a farm owned by a German company in South Carolina.

Ginkgo leaf extracts have been shown to have a wide range of biological activities. The most well-known use among American is the perceived ability of the products to improve short term memory. Other important effects include a protective effect on the blood-brain barrier and an anti-radical (antioxidant) effect. The leaf extracts has also been shown to increase vasodilation and peripheral blood flow rate in capillary vessels and end-arteries in various circulatory disorders. Ginkgo leaf helps to maintain integrity and permeability of cell walls by inhibiting lipid peroxidation of membranes. Other studies have shown vascular-tone regulating effects, and help in modulating cerebral energy metabolism.

Ginkgo extracts have been widely used in Europe for a wide variety of clinical conditions including vertigo, tinnitus (ringing in the ear), treatment of poor circulation, heart disease, eye diseases, chronic cerebral insufficiency, accidents involving brain trauma, dementia, and various conditions associated with senility. The standardized extract of the leaves has been shown to be beneficial in a broad range of conditions, including those involved with circulation, blood conditions, metabolism, immune function, varicose conditions, and post-thrombotic syndrome. It has been shown to help with short-term memory improvement (especially in older populations), and cognitive disorders secondary to depression, among other conditions.

New uses for Ginkgo leaf extracts are emerging as more is learned about the extracts usefulness in various clinical situations, especially those involving circulatory problems. For example, a 1991 study published in the Journal of Sex Education and Therapy evaluated the effect of Ginkgo leaf extract in the treatment of erectile dysfunction in fifty patients. The men, diagnosed with arterial erectile impotence, received 240 mg of ginkgo leaf extract daily for a period of nine months. The patients were divided into two groups based on their response to conventional therapies. Twenty of the patients had previously experienced some success with conventional drug therapy, and were placed in the first group. The second group of thirty patients had not experienced erection following conventional therapies.

Following treatment with the ginkgo leaf extract, all patients in the first group (20 men) regained sufficient and spontaneous erections following six months of treatment. Rigidity at both the tip and base of the penis were found to significantly improve after six months. The improvement continued through the nine-month treatment period. Nineteen of the thirty patients in the second group responded positively to the treatment, while eleven remained impotent. No side effects were reported in the study. This is only the second study published on the use of ginkgo leaf extracts in the treatment of impotence.

A Dutch research group has produced a retrospective analysis of ginkgo clinical studies, assessing their quality and reliability based on a number of objective parameters. They look at 40 clinical trials published since 1975 on the use of Ginkgo extracts in cerebral insufficiency. Clinical trials reporting results in healthy volunteers were excluded. The dosage was 120 mg/day of the ginkgo extract (given for at least 4-6 weeks). Of the 40 studies, eight were considered to be well-performed using rigorous scientific standards. The authors of the retrospective stressed the need for additional trials, in which double-blindness is checked, a larger number patients are involved, with better descriptions of randomization procedures, patient characteristics, and more effective measurement of data.

There is no doubt that ginkgo leaf extracts are of clinical benefit for a number of clinical conditions. More research will be published in the next few years that will further confirm ginkgo's utility.

References

  1. Sohn, M. and R. Sikora. 1991. Ginkgo biloba extract in the therapy of erectile dysfunction. J. Se Educ. Ther. 17:53-61.
  2. Kleijnen, J and P. Knipschild. 1992. Ginkgo biloba for cerebral insufficiency. Br. J. Clin. Pharmac. 34:352358.

 

 
       
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