Ginkgo biloba extract is made from the leaves of the maidenhair tree. (Photo by inoc)
The leaves of the maidenhair tree, Ginkgo biloba, are used in traditional medicine to treat various disorders. In recent years, the extract made from the leaves has also gained reputation as a possible memory and learning booster, as well as a natural treatment for Alzheimer's disease. But does it really work?
Unlike some other traditional medicines, Ginkgo biloba has actually been studied quite a bit. However, the results regarding its effects on brain function are inconclusive, which is why in this post, we'll take a closer look at what the current understanding of the matter is.
Ginkgo biloba and brain aging
Possibly the most interesting property of Ginkgo is its suggested ability to prevent or slow down brain aging, especially Alzheimer's disease. Unfortunately, many of the studies show rather disappointing results. A standard dose (120 mg) of Ginkgo biloba given for 6 months had no effect on cognitive functioning in patients with early stage dementia (link). Furthermore, in a study with over 3,000 participants, the same dose given for 6 years did not reduce dementia progression and Alzheimer's disease (AD) incidence compared to placebo (link).
However, a recent analysis found that a dose of 240 mg per day increased cognitive test scores in patients with AD and probable vascular dementia (link), suggesting that higher doses may be needed to see results. The timing of administration may also be important. In rats, Ginkgo had a positive effect on spatial memory tasks when given before the task, but no effect on memory when given after the task (link).
Degradation of amyloid precursor protein (APP) generates amyloid beta, which is the primary component of amyloid plaques found in the brains of Alzheimer's disease patients. In aged but not young mice, long-term treatment with high amounts of Ginkgo biloba extract have been shown to reduce APP levels in the cortex (link), which may partly explain the neuroprotective effect seen in some studies. In addition, Ginkgo seems to stimulate neurogenesis (link) and increase synaptic plasticity (link, link).
Combining Ginkgo with other compounds may increase its effectiveness. In one study, a composition of ginseng and Ginkgo extracts showed an improvement in hippocampal neurotransmitter status in APP transgenic mice (link). A combination of Ginkgo biloba, vitamin E, phosphatidylserine and pyridoxine had a long lasting positive effect on cognitive functioning in aged dogs (link).
Overall, the data on Ginkgo biloba's effect on brain aging is mixed. One review found that out of 34 placebo-controlled clinical trials, 21 showed significant benefits, 8 showed modest benefits, 4 showed a trend in favor of Ginkgo, and 2 found no advantage (link). Another recent review concluded that the evidence supporting the use of Ginkgo for dementia or cognitive impairment is inconsistent and unreliable (link).
Ginkgo biloba, stress and anxiety
Besides aging, cognitive impairment can also result from stress. In rats, Ginkgo biloba has been shown prevent learning and memory impairment and neuronal loss resulting from chronic stress (link, link) and to improve fear conditioning (link).
Though many studies have shown a cognitive benefit only in old animals, in one study, Ginkgo reduced anxiety also in younger human patients in a dose-dependent manner (link). Another one found a calming effect in healthy patients (link), which may be linked to Ginkgo's potential ability to reduce blood pressure during stress (link). In subjects between 50 and 65, depression, fatigue and anger were reduced with a daily dose of 240 mg (link).
On the other hand, a combination of Ginkgo biloba and Panax ginseng had no effect on mood, somatic anxiety, menopausal symptoms, sleepiness and cognition in post-menopausal women (link). Interestingly, however, one study found that both extracts had an effect on brain wave activity (link).
Ginkgo biloba in healthy people
Since Ginkgo is also sold as nootropic, a review of the studies on healthy people is in order. One study found an improvement from 120 mg Ginkgo in longer-term memory in old patients but no effect in young patients (link). An older study with middle-aged patients found that a dose of 240 mg resulted in increases in self-estimated mental health and quality of life and also an increase in motor performance compared to placebo (link).
A very large study including 3,500 volunteers aged between 35 and 80 years found no association between moderate doses of Ginkgo or ginseng and performance on learning and memory (link). A combination of Ginkgo and Bacopa monniera was also ineffective in healthy subjects (link). However, higher doses of Ginkgo (360 mg) and Panax ginseng (400 mg) may be needed to see cognitive benefits (link).
A reanalysis of three studies concluded that 120 mg of Ginkgo biloba modestly improves memory performance but may have a detrimental effect on the speed of attention task (link). However, a review of 15 randomized clinical trials suggests that several of the studies had methodological flaws, and that neither acute nor long-term administration has been shown to improve cognitive function in healthy young people (link).
Many studies have been done, but the evidence supporting Ginkgo biloba as a cognition enhancer remains inconclusive. Some studies have found a benefit while others show no effect. Based on the animal data, Ginkgo biloba has a neuroprotective effect and may help prevent cognitive decline resulting from aging and chronic stress. In humans, the case is less clear, especially when it comes to healthy, young people.
For more information on cognition and aging, see these posts:
L-Carnitine, Acetyl-L-Carnitine and Cognitive Function in Humans
Increasing Intelligence by Playing a Memory Game – Experiment Update
Caloric Restriction Improves Memory in the Elderly
Intermittent Fasting Reduces Mitochondrial Damage and Lymphoma Incidence in Aged Mice