Title

A Meta-Analysis of the Effects of Ginkgo Biloba on Cognitive and Psychosocial Functioning in Humans

Date of Award

2006

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Psychology

First Advisor

Mitchell E. Berman

Advisor Department

Psychology

Abstract

Ginkgo biloba is a commonly used herb for peripheral vascular disorders and is thought to improve memory. More than 1,000 clinical studies have examined the effects of ginkgo, and its potential mechanisms of action. Research to evaluate the clinical efficacy of ginkgo has predominantly focused on its potential neuroprotective effects in patients with cognitive impairment, but the effects of ginkgo on healthy individuals have also been examined. Previous authors have reviewed this literature. However, methodological limitations of earlier papers, the volume of new research not included in the original reviews, and identification of other potentially important processes previously overlooked, necessitated another comprehensive review. Therefore, the purpose of this study was to perform a meta-analysis examining the existing ginkgo literature, and further evaluate effect of standardized ginkgo extract treatment on psychosocial and cognitive functioning. Results revealed a significant overall effect for ginkgo. This effect appears to be population specific, such that ginkgo is effective for cognitively impaired older adults but not for healthy young adults. Ginkgo's effects also appear to be dependent upon the dose and duration of treatment. Statistically significant effects in favor of ginkgo were observed only for doses under 300mg. Ginkgo appears to work best when administered long term (15 days or greater). Furthermore, ginkgo affects various aspects of cognitive functioning differentially. Results suggest that ginkgo predominantly affects attention, simple reaction time/motor function, memory, and mental status/global functioning. The overall effect of ginkgo on measures of executive function and complex reaction time were non-significant. However, when the effect of ginkgo on executive functioning was partitioned by pre-treatment cognitive status, results revealed that cognitively impaired participants receiving ginkgo group performed significantly better than cognitively treated with placebo. Ginkgo also appears to have favorable effects on measures of psychosocial functioning including subjective reports of global functioning, activities of daily living and mood. Interestingly, though ginkgo's influence on various cognitive skill sets appear to be dependent on the population assessed (cognitively intact/impaired), its effects on measures of mood appear to be independent of pretreatment cognitive status.