Ginkgo: an herb to remember?

Many people take ginkgo—one of the top-selling herbal products in the U.S.—in hopes that it will sharpen their memory and concentration, as well as have other positive effects on mind and body. Can you believe any of the claims made for this ancient Chinese herbal medicine?

Ginkgo comes from the dried leaves of the maidenhair tree (Ginkgo biloba). It contains a complex mix of compounds, but researchers have focused primarily on two particular chemical groups—flavonoids and terpenoids—which together may improve blood flow, reduce blood clotting, and have anti-inflammatory, antioxidant, and neuro-protective effects. A standardized extract developed in Germany, EGb 761, is used in many clinical trials and is widely prescribed there and in France for “cerebral insufficiency,” which can mean anything from confusion, anxiety, and depression to headaches, tinnitus (ringing in the ears), and dementia. It’s also used for circulatory disorders, such as intermittent claudication (pain in the legs due to obstructed blood flow).

In the U.S. and Canada, ginkgo is sold as a dietary supplement, available in pills and tinctures.

Splashy headlines, assorted studies
Ginkgo made headlines in the U.S. about 10 years ago when a study in the Journal of the American Medical Association found that it improved mental and social functioning in some people with Alzheimer’s disease compared to a placebo, though the effects were small and short. The study looked only at people with dementia, but many healthy people assumed that ginkgo would boost their brain power, too—something that has never been proven.

Despite a flood of studies since then, it’s still not known if ginkgo can help with memory or other cognitive problems—or what dose or form would be best, or how long it should be taken.Studies in general have been small and poorly designed and have included people with a range of cognitive impairments, measured in different ways, which makes them hard to compare. Many studies have been funded by the company that makes the standardized extract. Among the recent findings:
• Alzheimer’s/dementia. In one of the few studies comparing ginkgo to drug treatment for Alzheimer’s, a small Italian study in 2006 found ginkgo as effective as donepezil in improving memory and attention in people with mild to moderate Alzheimer’s. However, a 2007 review of 35 studies by the Cochrane Collaboration, an international nonprofit research group, concluded that the overall evidence for ginkgo as a treatment for dementia or cognitive impairment is “inconsistent and unconvincing.” Results of two large trials, expected in a few years, should shed more light on whether this herb can slow or prevent dementia.
• Effects in “cognitively intact” older people. Fewer studies have looked at ginkgo’s effects on normal age-related memory decline—with mostly disappointing results. For example, ginkgo did not improve cognitive functioning in healthy older adults in a recent study in the Journal of the American Dietetic Association. And in a study in Human Psychopharmacology in 2006, it improved performance on one type of longer-term memory test, but had no effect on any other cognitive skill, including short-term memory and vocabulary.

Herbal hitches
Ginkgo appears to be safe, overall. Rare side effects include headache, stomach upset, palpitations, dizziness, and rashes. But because some cases of ginkgo-related bleeding have been reported, the herb should be avoided before surgery and used cautiously, if at all, with aspirin, ibuprofen, warfarin (Coumadin), or other drugs or supplements that affect blood clotting. It may increase the sedative effects of certain antidepressants or increase blood concentrations of some drugs used for treating hypertension.

Its safety in pregnancy or breastfeeding women is unknown.

Even if ginkgo helps some conditions, commercially available products may be different from the preparations used in clinical studies, so you may not get the same effects. Many ginkgo supplements sold in the U.S. claim to be standardized extracts , but that doesn’t mean they are the well-studied extract. Moreover, testing by ConsumerLab.com in 2005 found that several products were low in key compounds, or worse, had high levels of lead.

Bottom line
Though ginkgo is one of the best-studied herbs, we can’t recommend it because research findings have not been consistent and because the quality of supplements is so variable. There’s no convincing evidence it has any effect on memory or other mental functions in healthy older people—that is, it doesn’t seem to sharpen an already clear mind or help prevent what’s considered normal age-related memory loss. Nor is there evidence that it helps treat tinnitus or “cerebral insufficiency”; larger studies are needed to support its use for circulatory disorders. If you or a family member has Alzheimer’s or other dementia, you might talk to your doctor about ginkgo, but keep in mind, drug treatments may be better.

Ginkgo on the side: If you like the taste of ginkgo teas, go ahead and drink them, but don’t think that they have medicinal properties—ginkgo’s “active” ingredients are not water-soluble, so they would not be released into the tea. And don’t fall for claims that ginkgo-fortified foods, nutrition bars, and drinks will have any health benefits either. Most contain little, if any, ginkgo.

UK Berkeley Welness Letter Jan/08

Your Health and Mine