The unexpected positive effect on longevity has surfaced in research to determine ginkgo biloba's effect on age-related cognitive deficits, using rats as an animal model.

"At a certain point in our analysis, we realized that the rats who were receiving ginkgo biloba were living substantially longer than those who were not receiving the extract," said Jerrold C. Winter, professor of pharmacology and toxicology in the School of Medicine and Biomedical Sciences and author of the study.

"That finding leads us to speculate that in addition to ginkgo biloba's purported beneficial effects on brain function, which our study supports, the extract may also have a positive effect on longevity."

Results of the study appear in the current issue of Physiology and Behavior.

Ginkgo biloba is available in the U.S. as a dietary supplement, but is not approved by the FDA as a medical treatment. It is prescribed widely by physicians in Germany and France in the form of EGb 761-a complex mixture of chemicals obtained from ginkgo leaves-to treat age-related deterioration in brain function. Several human trials there have shown positive results, but little research has been done to replicate these findings in animals, Winter said.

Winter's earlier research with rats showed that a set of tasks performed in an apparatus called the radial maze could reliably detect deficiencies in learning and memory related to age. In the current study, Winter used 20-month-old rats, which were assigned a diet that included either ginkgo biloba extract or no extract. Over several weeks, the animals performed tasks in the radial maze that required them to master new challenges and retain learned information over time.

Results showed that rats receiving ginkgo biloba extract learned quicker and made fewer errors than control animals, and unexpectedly, lived an average of five months longer.

Winter found a significant positive relationship between the amount of active ingredient and degree of learning. The standard dose during most of the study was 50 mg/kg. However, one sub-group of animals was assigned to receive EGb 761 in doses of 100 mg/kg followed by 200 mg/kg, interspersed with periods when they performed tasks while receiving no extract.

Results showed that at the highest dose, errors declined by 50 percent.

"Despite the urgent need to discover drugs able to prevent, delay, ameliorate or cure age-related memory impairment and the degenerative dementias, progress has been slow," Winter stated in the article. Two major reasons for the lack of progress, he noted, are a lack of agreement on appropriate animal models and their applicability to humans when memory and cognition are concerned, and the absence of a drug proven to work in humans that could serve as a standard in animal tests.

"The present demonstration of positive effects of EGb 761 in animals, a substance for which abundant evidence exists of at least a modestly beneficial clinical effect in humans, is encouraging on both points," Winter said. "The challenge now is to identify, from this mix of perhaps 200 chemicals, which chemical or chemicals are producing these pharmacologic effects."

This study was supported in part by Dr. Willmar Schwabe Gmbh & Co. of Karlsruhe, Germany, manufacturer of EGb 761.