What is the benefit of ginkgo biloba supplements?
Continued interest in a traditional herbal remedy
The benefit of ginkgo biloba, the maidenhair tree, has long been recognized by traditional Chinese medicine with respect to a number of health disorders. In the West, the main interest centers on the benefit of ginkgo biloba supplements in preventing dementia and cognitive loss and improving memory. The benefit of this herb in relieving claudication (leg pain due to blocked arteries) has been supported by scientific studies. Results of studies on other benefits are inconsistent, although there is much anecdotal evidence from users claiming to have experienced the benefit of ginkgo supplements in a variety of conditions and diseases.
According to an overview by the University of Maryland Medical Center, Ginkgo biloba extract has been shown to improve circulation and thus could have an effect in conditions caused by decreased blood flow to the brain or other organs.
In addition, the flavonoids and terpenoids contained in the plant are potent antioxidants. Antioxidants act against the damaging effects of free radicals found in the environment or generated in the body. Free radicals cause tissue damage and also have a role in the development of cancer. Flavonoids have a protective effect on the cardiovascular system, nerves, and retina. Terpenoids dilate blood vessels and reduce platelet “stickiness” thus improving blood circulation.
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Relative benefits in various conditions
The MedlinePlus record for Ginkgo biloba lists the conditions in which supplements have been investigated in scientific studies and indicates the grade of scientific evidence for each use (classification runs from strongly positive (A), through good (B), unclear (C) to fairly negative (D)). The conditions include claudication (leg pain from blocked arteries, A), dementia (A), cerebral insufficiency (B), acute hemorrhoidal attacks (C), memory impairment (C), altitude sickness (C), asthma (C), cardiovascular disease (C), side effects of chemotherapy (C), chronic venous insufficiency (C), cocaine dependence (C), cochlear deafness (C), depression and seasonal affective disorder (SAD) (C), diabetic neuropathy (C), dyslexia (C), gastric cancer (C), glaucoma (C), Graves' disease (C), macular degeneration (C), memory enhancement (C),mood and cognition in post-menopausal women (C), multiple sclerosis (C), premenstrual syndrome (C), pulmonary interstitial fibrosis (C), quality of life (C), Raynaud's disease (C), diabetic retinopathy (C), tinnitus (C), schizophrenia (C), sexual dysfunction (C), stroke (C), vertigo (C), vitiligo (C), mental performance after eating (D). Side effects, safe dosage and potential interactions with other medications are also covered.
Cognitive benefit is a matter of controversy
Recent studies have raised some doubts about the benefit of Ginkgo supplements in the treatment of cognitive decline and dementia. These are summarized below as well as the limitations of the studies leading to such statements.
An updated Cochrane review, published in 2009, assessed the safety and benefit of Ginkgo biloba in the treatment of existing cognitive impairment and dementia. The review was based on an analysis of 36 randomized, double-blind, placebo-controlled studies identified from the medical literature and other sources.
It was found to be a safe treatment, with no differences in side effects noted between participants given supplements and subjects given placebo. The authors of the review criticised some of the earlier studies for having very small groups of subjects and for their unsatisfactory methodology. Results from more recent trials were inconsistent. Three out of the four most recent studies found no difference between Ginkgo and placebo, while one found very large differences in favor of the herb. The authors of the review concluded: “The evidence that Ginkgo biloba has predictable and clinically significant benefit for people with dementia or cognitive impairment is inconsistent and unreliable.”
Also in 2009, Snitz and colleagues reported further results from the Ginkgo Evaluation of Memory (GEM) study, the largest single clinical study so far conducted on the effects of this herbal remedy in preventing cognitive decline and dementia. The study included 3069 subjects aged 72-96 years and was conducted in 6 US academic medical centers between 2000 and 2008. Subjects were followed-up for a median period of 6.1 years. The subjects received 120 mg of Ginkgo biloba extract or placebo twice daily.
The study did not find any decrease in the incidence of dementia, due either to Alzheimer disease or to other causes, in subjects given supplements. Furthermore, no effects were observed on overall age-associated changes in cognition, nor on changes in memory, attention, language or other specific cognitive parameters.
The authors themselves admit that the study had certain limitations. The most important of these is that the results of three neuropsychological tests were better in the placebo group right at the very outset of the study. This potentially could have masked some subtle differences between the group given placebo and the group given supplements. However, the authors claim that the differences in test results were small and not clinically significant.
Herbal company defends cognitive benefits
The results from the GEM study have been hotly disputed in a statement released by Dr. Willmar Schwabe GmbH & Co. KG, a herbal medicines company based in Karlsruhe, Germany, which manufactures ginkgo biloba supplements. The company director, Professor Michael Habs stated: “The current paper, describing secondary analyses of data from a previously published study, is methodologically so weak that it is of limited relevance.” The main criticism concerns the fact that cognitive decline was very slight, even in the placebo group. Dr Guenter Meng, Head of R&D at Schwabe, considers that the study would need to have continued for another ten years at least to obtain a level of cognitive decline that would enable any conclusions to be made. Another criticism is that 40% of study participants had actually stopped taking the supplements or placebo by the time of the secondary analyses.
In addition, positive results reported from earlier studies cannot be disregarded. It is clear from the MedlinePlus information given above that more gingko biloba research is required before the benefit of supplements can be truly assessed,
Safety and side effects of gingko biloba
As of now, these supplements continue to be widely prescribed and herbal tea prepared from this plant is generally considered to be a safe remedy. The main concerns are that it may cause allergic reactions in individuals who are allergic to poison ivy. It also increases the risk of bleeding and therefore should be avoided by people with bleeding disorders or immediately before surgery.
Ginkgo biloba seeds are potentially deadly and should not be consumed under any circumstance.
Like other herbal remedies, gingko biloba can interact with medicines to cause potentially dangerous side effects.
Persons who do not have the risk factors listed above may safely take the supplements for the conditions listed under categories A to C in Medline Plus. Ginkgo biloba supplements are widely available at moderate prices, both online and locally.