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UC Davis Health System

UC Davis Health System

Can the oldest living tree species help prevent dementia?

Photo of ginkgo biloba tree
The Gingko tree is the sole surviving species of a group of Gymnosperms that flourished 65 million years ago, the time when dinosaurs existed.

You've been looking for your glasses for more than an hour, only to discover they've been resting quietly on the top of your head. You've gotten up from the sofa during a commercial break and by the time you make it to the kitchen, you've forgotten what you intended to do there.

Most of us have experienced forgetfulness from time to time, but as we age, the episodes can become more frequent — and distressing. For some people, changes in memory can become extreme, culminating in what doctors commonly refer to as “dementia.” The most well-known form of dementia is Alzheimer's disease, a degenerative disorder caused by death of nerve cells that results in a steady loss of memory and cognitive skills.

“While some memory loss occurs as part of normal aging, many people can and do remain active and mentally alert,” said John Robbins, UC Davis professor of internal medicine. “Researchers across the nation are studying the impact of factors like genes, diet, environmental conditions and herbal supplements to better understand the characteristics, qualities and habits of those who age well. At UC Davis, we're looking at Ginkgo biloba and how this ancient, time-honored tree can delay or even prevent memory loss.”

Exotic name, great potential

With no living relatives, ginkgo biloba is one of the best-known examples of a living fossil. The Chinese considered it a sacred tree and cultivated it for medicinal purposes. Throughout the ages, the tree has been hailed for healing myriad ailments such as asthma, fatigue and bronchitis.

While ginkgo's ability to affect memory has been studied throughout Europe, very little research had been done in the United States until 2000, when UC Davis researchers began participating in the National Institutes of Health -sponsored “Ginkgo Evaluation of Memory Study” — a research project designed to determine if ginkgo can not only relieve symptoms of memory loss, but also prevent it from occurring in the first place. The project is a collaboration among researchers from UC Davis, Johns Hopkins University, the University of Pittsburgh and Wake Forest University School of Medicine.

Between 2000 and 2002, UC Davis recruited more than 900 of the 3,000 study volunteers by visiting such places as community centers and churches, and through direct mail and newspaper notices. Half of the participants take 240 milligrams of ginkgo biloba per day — derived from extracts of the ginkgo leaves — while the remainder take a placebo (pills that do not contain ginkgo biloba).

When the study is completed, the two groups will be compared to determine whether memory, thinking and personality have changed, and to see if the plant has been effective in preventing those changes.

So far, participants in the study — both those taking ginkgo and those taking placebos — have had less dementia and less mortality than predicted, according to principal investigator Robbins.

Healing leaves

The brain is an intricate mix of neurons, connections and pathways that must stay healthy for the brain to function well. With dementia or Alzheimer's, the nerve cells in effect tangle up and develop deposits of amyloid, or starch-like, substances in the brain.

“Ginkgo biloba may slow down or stop this breakdown,” said Robbins. “Compounds in the leaf act as antioxidants, which means they may fight off diseases and perhaps increase blood circulation to the brain and protect nerve cells.” Ginkgo's antioxidant and free-radical scavenging abilities have been widely studied. In fact, the herb's antioxidant power also may be useful in preventing and treating cardiovascular and peripheral vascular disease.

Because ginkgo is purported to enhance memory and possibly prevent and heal heart and vascular diseases, it is one of the country's top-selling herbal supplements, bringing in millions to manufacturers each year. Consumers can find various preparations of ginkgo biloba extract over the counter, but the products vary in content and active ingredients. While research into its ability to prevent or delay dementia holds great promise, studies into the herb's effectiveness and safety are ongoing and no specific daily amount of ginkgo can be recommended as safe or effective.

Researchers are holding out hope that the much-revered tree leaves can help stop dementia and other memory problems in their tracks. But according to Robbins, the study might just prove to help the pocketbook, not the brain.

"When this study comes to an end in the next six to 12 months, we will have an answer," he said. "Either ginkgo helps to prevent dementia, or Americans should stop spending millions of dollars on a product that doesn't work."

A note of caution: Check with your doctor before taking any herbal or over-the-counter supplements. In addition to causing potential unpleasant side effects, they can interact with any prescription drugs you may be taking. For example, those taking blood-thinning drugs like Coumadin (warfarin) should not take ginkgo biloba.