03/18/2010 05:12 am ET | Updated Nov 17, 2011

Ginkgo Biloba And Alzheimer's Disease

The herb, Ginkgo biloba, has been used by many Americans in the hope of improving memory and forestalling Alzheimer's Disease. A new report disparages this use, but doubts about the efficacy of Ginkgo are not new. In my book, Beyond Alzheimer's: How to Avoid the Modern Epidemic of Dementia, I included a discussion of Ginkgo biloba, and I did not recommend its use.

The Ginkgo tree, with the scientific name of Ginkgo biloba, is often referred to as a living fossil. It has descended largely unchanged from its ancestors that lived over 250 million years ago. An interesting characteristic of the Ginkgo tree is that it is dioecious, that is, individual trees are either male or female. However, I doubt that they enjoy much of a night life.

The Ginkgo has been used for food as well as for medicinal purposes for thousands of years. In the 1980's an extract of Ginkgo, called EGb 761, became popular in Germany as a treatment for memory loss. In 1988 alone, German doctors wrote more than 5 million prescriptions for EGb 761. In the 1980's Ginkgo became a popular treatment for memory loss in the United States. Its popularity grew, and in 2007 Americans spent over 100 million dollars on Ginkgo preparations.

Ginkgo biloba contains substances known as flavonoids and terpenoids that may have medicinal properties. Test tube data has suggested that Ginkgo contains substances that could block or reverse several different neurodegenerative processes that lead to loss of cognitive function. One of the most well documented effects of ginkgo is improvement in blood flow, which could improve blood supply to the brain and thus improve cognitive function in individuals whose blood supply is compromised. This is not uncommon in elderly patients. Another well known effect is a decrease in the likelihood of blood clotting, which is due to the terpene molecule, ginkoglideB, blocking some of the effects of platelet-activating factor (PAF). Platelets are cell-like structures in the blood that stick together and initiate clotting of blood. PAF also participates in triggering some inflammatory processes, and it is thought to play a role in some of the damaging effects of inflammation on neurons in the brains of patients with various forms of neurodegenerative dementia. Ginkgo has been found to reduce the inflammatory damaged stimulated by amyloid deposition in brain tissue, and it was thought to be due to its ability to block the effects of PAF. Unfortunately, Ginkgo's anti-platelet effects may have led to its implication in a number of cases in which individuals suffered significant bleeding events while taking the herb.

There are animal studies showing that Ginkgo extracts can slow the growth rate of amyloid deposits in the brain. The build up of amyloid in brain tissue is one of the major hallmarks of Alzheimer's. Ginkgo is an antioxidant and free radical scavenger, which would make a Ginkgo extract a useful defense against the damage of oxidative stress. There is also a report that Ginkgo stimulates neurogenesis in the brains of mice that have been genetically altered to develop amyloid plaques in their brains very similar to those that develop in people with Alzheimer's Dementia.

Treatment with Ginkgo biloba extract improves learning and memory in both young and old rats. It also improves learning and memory in rats that are stressed during the learning of their behavioral tasks. Perhaps most impressive are results showing that treatment with Ginkgo can improve learning and memory in the mice that are studied as animal models of Alzheimer's Dementia.

Together, the scientifically established effects of Ginkgo on the brain and its blood supply, as well as results from animal studies of learning and memory, would suggest that it could offer significant benefits in the prevention and treatment of Vascular and Alzheimer's Dementia. In fact, several studies have shown that Ginkgo is helpful in the treatment of dementia. In one recent study performed in 2007, the Ginkgo extract EGb 761 was found to improve cognitive function in patients with mild to moderate Vascular or Alzheimer's Dementia. Another study in 2007 found EGb 761 to have effects equal to those of the prescribed medication Aricept in slowing the rate of decline in patients with moderately severe Alzheimer's Dementia.

Unfortunately, the clinical data has not been consistent in showing ability to prevent cognitive loss in normal elderly subjects, or to improve cognitive function in patients already diagnosed with Alzheimer's Dementia. In 2007, the Cochrane reviewers, a well respected English research group dedicated to studying and publishing reports on various medical treatments, stated that effects of Ginkgo on dementia are "inconsistent and unconvincing". One of the most disappointing studies, funded by the Alzheimer's Society and led by Dr. Steven DeKosky of the School of Medicine at the University of Virginia, found that 6 months of treatment with "a standard dose of high purity Ginkgo biloba" offered no benefits whatsoever in relieving or preventing progression of cognitive symptoms in patients with mild to moderate Alzheimer's Dementia. The newest report, also from DeKosky and published in latest issue of JAMA, revealed that people between the ages of 72 and 96 who took the herb for six years showed no differences in attention, memory, and other cognitive measures compared to those who took the placebo.

It is critical to note that in the above studies, as in most studies of herbs and nutraceuticals in the treatment and prevention of Alzheimer's Disease, the use of Ginkgo in people over the age of 70 who have already developed significant symptoms of dementia is likely to be too little, too late. Indeed, the degenerative changes in brain tissue begin at least 15 to 20 years before they appear as losses in cognitive function. Would it have made a difference if the Ginkgo was started at a much earlier age and continued for more years? Perhaps. On the other hand, there is no one herb or medication that can prevent dementia. Prevention requires changes in diet and lifestyle that go far beyond such simple measures. In any case, because lack of clear evidence of its benefit, and availability of other supplements that do appear to be helpful without significant risks such as bleeding, Ginkgo, at least if used all on its own, is probably not the herb for you.