The ginkgo tree is one of the oldest on earth, dating back more than 225 million years, and its leaves are among the most unique in appearance. As an herbal remedy, Ginkgo biloba extract is extremely popular, repeatedly making top-selling lists in both the United States and Europe. The standardized extract of ginkgo leaves is also among the most established; however, it has become among the most adulterated.
Ginkgo has many uses in human health. The ABC Clinical Guide to Herbs, published by the American Botanical Council (ABC) and its founder Mark Blumenthal, cites cerebral insufficiency, vertigo/tinnitus and peripheral vascular disease as the primary uses of ginkgo, with other potential uses, including acute altitude sickness, hypoxia, acute cochlear deafness and sexual dysfunction associated with the use of SSRIs (selective serotonin reuptake inhibitors). Despite this long list of benefits, ginkgo has made its name in the natural remedies arena as a memory enhancer.
Ginkgo achieves these results by improving blood flow to tissues, including the brain, and by enhancing cellular metabolism. The root of these mechanisms is in the flavonoids and terpene lactones found in ginkgo leaves. The primary flavonol glycones in ginkgo are quercetin, kaempferol and isorhamnetin; the terpenes include ginkgolides (A through J) and bilabolides.
The flavanols handle ginkgo's antioxidant actions, including free radical scavenging. They also increase serotonin release and reuptake, stimulate choline uptake in the brain (hippocampus) and inhibit nitric oxide (NO) formation. For their part, ginkgolides support endothelium relaxation and inhibit platelet activating factor (PAF), which is involved in platelet aggregation, blood vessel constriction, neuronal plasticity and neuronal inflammation response. Bilobalides enhances cognition by affecting GABA receptors in the brain, and protects against ischemic injury and neuronal death via antioxidant and gene-protective mechanisms.
Based on these active constituents, the first standardized extract of ginkgo leaves by German company Dr. Willmar Schwabe GmbH were created around 1965 and focused on flavonol glycone and terpene lactone content. Dr. Schwabe and company developed an extract standardized to 24 percent flavonol glycosides and 6 percent terpene lactones. The first extract was based on a 10:1 ratio of leaves to final extract, but the eventual standard became an average 50:1—"This means that from 100 kg of dried ginkgo leaves, only 2 kg of the extract are obtained," explained Jochen Muelhoff, Ph.D., Schwabe. Actual acceptable ratios on the market range from 35 to 67 leaves per pound of extract, according to Blumenthal.
In its early years, this standardized Ginkgo biloba extract (GBE) targeted cerebral and peripheral blood flow and won approval from the German government as a pharmaceutical for the treatment of cerebral insufficiency—memory loss related to dementia or degenerative neurological diseases such as Alzheimer's disease. Germany also approved GBE for the treatment of tinnitus, vertigo and claudication (poor circulation in the legs). GBEs in Europe have since been required to adhere to the 24/6 (really within the range of 22-27/5-7) standardization, and must also contain less than 5 ppm (parts per million) of ginkolic acid, a toxic compound found in lesser amounts in ginkgo leaves than in seeds. The German Commission E monograph, which guides herbal medicines in Germany, also stipulates exact content of the terpenes ginkgolide A, B and C (2.8 percent to 3.4 percent) and bilobalide (2.6 to 3.2 percent).
The Germans and Schwabe literally set the standard for standardized GBE, as 24/6 extracts became the prevailing therapeutic ginkgo product on the market. The difference is regulations in the rest of the world, including the United States, have not quite caught up to the detailed level of the Germans and European Union on constituent content. Of course, this level of GBE is sold as a medicine in Germany, but as a dietary supplement in the United States.
The main U.S. regulation relative to the 24/6 ratio or specific content levels of key flavonoids and terpenoids is that a finished product must be labeled correctly relative to its contents. Thus, if a product says it has a specific level of flavonoids or terpenoids, it must say so on the label, which must also accurately reflect the nature of those compounds. If the contents don't match the label, the product is misbranded; if there are extra ingredients in the product that are not listed on the label, the product is also adulterated.