Traceable back 300 million years, the ginkgo is the oldest surviving species of tree. Although it died out in Europe during the Ice Age, ginkgo survived in China, Japan, and other parts of East Asia. It has been cultivated extensively for both ceremonial and medical purposes, and some particularly revered trees have been lovingly tended for more than 1,000 years.
In traditional Chinese herbology, tea made from ginkgo seeds has been used for numerous problems, most particularly asthma and other respiratory illnesses. The leaf was not used. But in the 1950s, German researchers started to investigate the medical possibilities of ginkgo leaf extracts rather than remedies using the seeds. Thus, modern ginkgo preparations are not the same as the traditional Chinese herb, and the comparisons often drawn are incorrect.
The standard dosage of ginkgo is 40 mg to 80 mg 3 times daily of a 50:1 extract standardized to contain 24% ginkgo-flavone glycosides. Levels of toxic ginkgolic acid and related alkylphenol constituents should be kept under 5 parts per million.
In an analysis performed in 2006 by the respected testing organization ConsumerLab.com , some tested ginkgo products were found to be contaminated with lead. ^
What Is the Scientific Evidence for Ginkgo?
#Alzheimer’s Disease and Non-Alzheimer’s Dementia
In the past, European physicians believed that the cause of mental deterioration with age (senile dementia) was reduced circulation in the brain due to atherosclerosis. Since ginkgo is thought to improve circulation, ^ ^ they assumed that ginkgo was simply getting more blood to brain cells and thereby making them work better.
However, the contemporary understanding of age-related memory loss and mental impairment no longer considers chronically restricted circulation the primary issue. Ginkgo (and other drugs used for dementia) may instead function by directly stimulating nerve-cell activity and protecting nerve cells from further injury, ^ although improvement in circulatory capacity may also play a role.
Numerous double-blind, placebo-controlled studies have found ginkgo extract effective for dementia; among these, studies rated as “high quality” by accepted scientific norms included a total of more than 2,000 people. ^ For example, one major US trial published in 1997 enrolled more than 300 people with Alzheimer’s disease or non-Alzheimer’s dementia. ^ Participants were given either 40 mg of Ginkgo bilobaextract or placebo 3 times daily for a period of 52 weeks. The results showed significant but not entirely consistent improvements in the treated group.
Another study, published in 2007, followed 400 people for 22 weeks, and used twice the dose of ginkgo. ^ The results of this trial indicated that ginkgo was significantly superior to placebo. (Technically, it was superior in the primary outcome measure, the SKT cognitive test battery, as well as on all secondary outcome measures.) The areas in which ginkgo showed the most marked superiority as compared to placebo included, “apathy/indifference, anxiety, irritability/lability, depression/dysphoria and sleep/nighttime behaviour.”
In addition, a 6-month study found ginkgo equally effective as the drug donepezil (taken at a dose of 5 mg daily). ^ On the other hand, one fairly large study drew headlines for finding ginkgo extract ineffective. ^ This 24-week, double-blind, placebo-controlled study of 214 people with either mild to moderate dementia or ordinary age-associated memory loss found no effect with ginkgo extract at a dose of 240 mg or 160 mg daily. However, this study has been sharply criticized for a number of serious flaws in its design. ^ But in another community-based study among 176 elderly subjects with early-stage dementia, researchers found no beneficial effect for 120 mg of ginkgo extract given daily for six months. ^ The ability of gingko to prevent or delay a decline in cognitive function is less clear. In a placebo-controlled trial of 118 cognitively-intact adults 85 years or older, gingko extract seemed to effectively slow the decline in memory function over 42 months. The researchers also reported a higher incidence of stroke in the group that took gingko, a finding that requires more investigation (see Safety Issues below). ^ In a 2009 review of 36 randomized trials involving 4,423 patients with declining mental function (including dementia), researchers concluded ginkgo appears safe but there is inconsistent evidence regarding whether it works. ^
#Enhancing Mental Function in Healthy People
Ginkgo has shown less consistent promise for enhancing mental function in people who experience the relatively slight decline in cognitive function that typically accompanies increased age.
For example, in a double-blind, placebo-controlled trial, 241 seniors complaining of mildly impaired memory were given either placebo or ginkgo for 24 weeks. ^ The results showed that ginkgo produced modest improvements in certain types of memory.
Another double-blind, placebo-controlled trial examined the effects of ginkgo extract in 40 men and women (ages 55 to 86) who did not suffer from any mental impairment. ^ Over a 6-week period, the results showed improvements in measurements of mental function.
Possible benefits were seen in six other trials as well, involving a total of about 250 people. ^ Set against these positive findings is the 24-week study mentioned above, which found no benefit in ordinary age-related memory loss. ^ The reason for this negative outcome may be flaws in this trial’s design, as noted above. ^ However, three other studies enrolling a total of about 400 seniors also failed to find significant benefit with daily use of ginkgo. ^ Another double-blind, placebo-controlled study used a one-time dose of ginkgo, and again found no benefits. ^ Besides these negative trials, there is another weakness in the evidence: inconsistency even among positive trials. There are numerous measurable aspects of memory and mental function, and studies of ginkgo have examined a great many of these. Unfortunately the exact areas of benefits seen vary widely.
For example, in one positive study, ginkgo may speed the ability to memorize letters but not expand the number of letters that can be retained; while in another positive study, the reverse may be true. This type of inconsistency tends to decrease the confidence one can place in these apparently positive studies, because if ginkgo were really working, one would expect its effects to be more reproducible.
A total of about 15 controlled trials have examined the effects of ginkgo on memory and mental function in younger people. ^ However, again, results are inconsistent, with many negative results, and the positive ones failing to indicate a consistent pattern of benefit. ^ Several small double-blind, placebo-controlled studies have evaluated combined treatment with ginseng or vinpocetine for enhancing mental function in young people. ^ The results, overall, are unconvincing. Weak evidence suggests that combining phosphatidylserine with ginkgo might increase its efficacy. ^ In two studies, ginkgo combined with the Ayurvedic herb brahmi failed to improve mental function. ^ The bottom line: It’s not clear whether ginkgo actually enhances memory and mental function in healthy seniors or healthy younger people. Benefits, if they do exist, are probably slight.
In intermittent claudication , impaired circulation can cause a severe, cramp-like pain in one's legs after walking only a short distance. According to 9 double-blind, placebo-controlled trials, ginkgo can significantly increase pain-free walking distance. ^ One double-blind study enrolled 111 people for 24 weeks. ^ Subjects were measured for pain-free walking distance by walking up a 12% slope on a treadmill at 3 kilometers per hour (about 2 miles per hour). At the beginning of treatment, both the placebo and ginkgo (120 mg daily) groups were able to walk about 350 feet without pain. By the end of the trial, both groups had improved, although the ginkgo group improved significantly more. Participants taking ginkgo showed about a 40% increase in pain-free walking distance as compared to only a 20% improvement in the placebo group.
Similar improvements were also seen in a double-blind, placebo-controlled trial of 60 people who had achieved maximum benefit from physical therapy. ^ A 24-week, double-blind, placebo-controlled study of 74 people with intermittent claudication found that ginkgo at a dose of 240 mg per day was more effective than at 120 mg per day. ^ A 2009 review of 11 trials with 477 subjects suggested that those who took ginkgo biloba were able to walk further than control patients, although the results were limited by differences among the trials. ^ However, not all studies have been positive. In a randomized trail involving 62 individuals (averaging 70 years of age), 300 mg of ginkgo per day was no better than placebo at improving pain-free walking distance over 4 months of treatment. ^
One double-blind, placebo-controlled study evaluated the benefits of ginkgo extract for women with PMS symptoms. ^ This trial enrolled 143 women, 18 to 45 years of age, and followed them for two menstrual cycles. Each woman received either the ginkgo extract (80 mg twice daily) or placebo beginning on day 16 of the first cycle. Treatment was continued until day 5 of the next cycle, and resumed again on day 16 of that cycle. As compared to placebo, ginkgo significantly relieved major symptoms of PMS, especially breast pain and emotional disturbance. In another similarly designed trial involving 85 university students, Ginkgo biloba L.significantly reduced PMS symptom severity compared to placebo. ^
In a double-blind, placebo-controlled study of 107 people with various forms of anxiety (specifically, generalized anxiety disorder or adjustment disorder with anxious mood), ginkgo extract taken at a dose of 240 mg or 480 mg daily proved significantly more effective than placebo. ^
Macular degeneration , one of the most common causes of vision loss in seniors, may respond to ginkgo.
In a 6-month, double-blind, placebo-controlled study of 20 people with macular degeneration, use of ginkgo at a dose of 160 mg daily resulted in improved visual acuity. ^ A 24-week, double-blind study of 99 people with macular degeneration compared ginkgo extract at a dose of 240 mg per day with ginkgo at a dose of 60 mg daily. ^ The results showed that vision improved in both groups, but to a greater extent with the higher dose.
A 3-month, double-blind trial of 70 people with a variety of vertigo conditions found that ginkgo extract given at a dose of 160 mg twice daily produced results superior to placebo ^ By the end of the trial, 47% of the people given ginkgo had significantly recovered versus only 18% in the placebo group.
A small double-blind, placebo-controlled trial found that use of ginkgo extract at a dose of 120 mg daily for 8 weeks significantly improved the visual field in people with glaucoma . ^
Studies of Ginkgo bilobaextract for treating tinnitus have yielded conflicting results. ^ While some small studies found benefit, the largest and best-designed of these trials failed to find ginkgo effective. In a 12-week, double-blind trial, 1,121 people with tinnitus were given either placebo or standardized ginkgo at a dose of 50 mg 3 times daily. ^ The results showed no difference between the treated and the placebo groups.