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How Ginkgo works
Standardized preparations of Ginkgo biloba are widely used in Europe to treat dementia and other neurodegenerative diseases, and in recent years the extracts of G. biloba have become widespread in North America. Most commercially available Ginkgo preparations are standardized to two bioactive constituents: 24% flavone glycosides, and 6% terpenoids. The flavonoid constituent functions as a strong anti-oxidant and is believed to have a general neuroprotective effect. Animal studies have confirmed that the terpenoid fraction antagonizes platelet activating factor (PAF), facilitating post-stroke recovery through vascular re-perfusion by decreasing thrombosis and nerve cell death associated with cerebral ischemia (Smith 1996). Constituents of Ginkgo may inhibit neurotoxicity and nerve-cell death caused by nitric oxide (Zhao 2002). Other postulated beneficial mechanisms of Ginkgo biloba include vasodilation of small blood vessels in the brain and general anti-inflammatory effects (Blumenthal 2000). EEG changes associated with increased alertness have been found in healthy adults taking Ginkgo preparations (Pidoux 1986). Therapeutic doses range from 40 mg three times daily up to 600mg/day in divided doses. Studies have reported sustained improvement in cognitive functioning following three months of treatment.
Findings of studies on G. biloba in dementia are inconsistent
Systematic reviews and meta-analyses of double blind studies have concluded that standardized preparations of Ginkgo biloba in doses between 120 and 600mg/day taken over durations of several weeks to one year result in consistent modest improvements in memory, general cognitive functioning, and activities of daily living in mild to moderate cases of both Alzheimer’s dementia and multi-infarct dementia that are equivalent to improvements seen with donepezil ™, a conventional cholinesterase inhibitor (Wong 1998; Ernst 1999; Kanowski 1997; Oken 1998; Le Bars 1997). In contrast to these positive findings, another meta-analysis pointed out inconsistent findings of three trials based on more rigorous methodologies and remarked on research design problems in those studies and other earlier trials including the absence of standardized preparations and the use of different dementia rating scales across studies (Birks 2004).
Although most controlled studies fail to support the claim that Ginkgo significantly improves memory in severely demented patients, the findings of one double blind study suggest that the rate of overall cognitive decline may be moderately slowed in this population (Le 2002). Standardized preparations of Ginkgo are also used to treat cognitive impairments due to vascular insufficiency and traumatic brain injury (Gaby 1996). An early systematic review of 40 studies (Kleijnen 1992) concluded that Ginkgo improves many cognitive symptoms associated with cerebral vascular insufficiency, including impaired concentration and memory loss. In contrast to Alzheimer’s patients, greater improvement was reported with Ginkgo in individuals diagnosed with vascular dementia who had severe memory impairment compared to individuals with mild memory impairment.
Combining Ginkgo and Ginseng may improve memory in healthy non-demented individuals
Combining Ginkgo biloba with Ginseng (Panax ginseng) enhances memory performance in non-impaired individuals more than either natural product alone. Randomized placebo-controlled studies have concluded that a compound herbal product containing both Ginkgo biloba (160 or 320mg) and Panax ginseng 400mg significantly improves recall performance in healthy middle-aged adults (Kennedy 2001; Wesnes 2000; Wesnes 1997). Enhanced cognitive functioning appears to reach its peak approximately 6 hours after the herbal preparation is taken. Combining Ginkgo with another traditional Chinese herbal, Dangshen (Codonopsis pilosula), may also have more beneficial effects on learning and memory in healthy adults compared to either herbal alone (Singh 2004).
Safety problems associated with G. biloba
Side effects associated with Ginkgo are infrequent and typically mild, including rash and headache. Mild transient adverse effects include upset stomach, dizziness, and headaches. Ginkgo taken alone does not increase the risk of bleeding, however, the use of Ginkgo preparations should be avoided in individuals taking anti-coagulants. Because of its strong anti-platelet aggregation factor (PAF) profile, G. biloba extract increases the risk of bleeding, and concurrent use should be avoided in patients taking aspirin, warfarin, heparin or other medications that interfere with platelet activity and increase bleeding time. Because of the risk of increased bleeding, G. biloba preparations should be discontinued at least two weeks prior to surgery. G. biloba preparations have been reported to result in the elevation of hepatic enzymes, and there are case reports of possible serotonin syndrome when taken with serotonin-selective reuptake inhibitors (SSRI).
To learn about other non-pharmacologic approaches for treating dementia or mild cognitive impairment, or slowing the rate of memory loss the reader is referred to my e-book "Dementia and Mild Cognitive Impairment: The Integrative Mental Health Solution."
