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Ginkgo biloba extracts appear to be effective in modulating reactions to inflammatory and oxidative stress and in regulating neurotransmission, with preliminary evidence of beneficial effects in disorders of attention, learning and memory, including age-associated memory impairment, AD/HD, and Alzheimer’s disease. The precise mechanism of action is unclear, but evidence suggests a capacity to avert free radical-induced damage through inhibition of membrane breakdown, protection against age-related hippocampal degeneration, and effects on monoamine transmission. The antioxidant potential of ginkgo constituents is demonstrated by their ability to down-regulate mediators of free radical-induced damage, such as superoxide dismutase, lipid peroxide products, and phospholipids;2 inhibit products of hypoxia-induced membrane breakdown, including choline-containing phospholipids;3 antagonize the anticoagulant effects of platelet activating factor;4 and improve vascular relaxation, through inhibition of nitric oxide.5,6 Together, these effects work to improve cerebral blood flow. Few controlled studies on the cognitive-enhancing effects of ginkgo have been performed in humans, despite its popularity. A randomized, double-blind, placebo-controlled study in mildly to severely demented patients with Alzheimer’s disease or multi-infarct dementia showed stabilization or improvement of cognitive performance and social functioning after six to 12 months of treatment with EGb 761 ginkgo extract (120 mg/d). In subjects with age-associated memory impairment, automatic information processing was improved after both acute and chronic (57 days) ginkgo biloba extract administration.12 Assessment of memory processing was based on reaction time in electrophysiologic testing (P300 evoked potential).
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