Ginkgo Biloba - Scientific Background
Extracts prepared from ginkgo leaves affect the circulatory system and functions of the brain and nervous system (Smith et al 1996; Itil and Martorano 1995).
Ginkgo may alleviate some symptoms of brain deterioration (dementia).
Most well-designed clinical studies show that ginkgo improves symptoms in patients who are suffering from the kind of dementia that is due to impaired blood supply to the brain (Kleijnen and Knipschild 1992; Hopfenmüller 1994).
In the largest recent clinical trials among patients with dementia of the Alzheimer's type or dementia that is due to multiple areas of cell death in the brain (multi-infarct type), the extract of Ginkgo biloba (EGb 761) showed mixed results. The extract resulted in symptomatic improvements that were large enough for caregivers to notice although the overall physician evaluations (clinical global impression) were unchanged (Kanowski et al 1996; Le Bars et al 1997).
Ginkgo may improve blood circulation.
Similar improvements are documented for patients with insufficient peripheral blood flow (intermittent claudication). Among patients with intermittent claudication that was confirmed by X rays, both total walking distance and pain-free walking distance increased significantly for those randomized to receive ginkgo compared to those who received a placebo. However, the ultrasound measure of the rate of circulation through the legs (Doppler index) was unaffected (Blume et al 1996; Peters et al 1998).
Ginkgo's effects on memory may depend on age.
While no effect on memory has been observed among younger healthy volunteers, some measures of mental (cognitive) performance appeared to improve in a placebo-controlled study of 31 elderly outpatients who were suffering from mild or moderate memory impairment (Warot et al 1991; Rai et al 1991).
Ginkgo may relieve symptoms of some forms of ringing of the ears (tinnitus).
A possible effect of ginkgo extract in relieving symptoms of tinnitus was recently confirmed (Holgers et al 1994; Meyer 1986).
Because tinnitus has many causes in addition to disorders of the blood supply to the brain, it remains to be seen what proportion of tinnitus sufferers will find relief by using ginkgo.
Ginkgo has antioxidant functions.
Some of these effects may be due to the ability of Ginkgo biloba extracts to inhibit the formation of oxygen free radicals. Experimental studies in animals (Karcher et al 1984) and humans (Schaffler and Reeh 1985) show a protective effect of Ginkgo biloba against tissue damage and impairment of function due to insufficient oxygen, which can trigger excessive oxygen-free radical activity.
