Ginkgo biloba has no beneficial effect on memory and related mental functions of healthy older adults when taken following manufacturer's instructions, according to a study in today's issue of the Journal of the American Medical Association (JAMA).
The study on the botanical which is marketed worldwide as an enhancer of memory and other mental functions has caused strong reactions by several industry bodies and gingko biloba manufacturers, all urging the media and consumers to consider the study within a wider context.
In 1998, $310 million (€316m) worth of gingko biloba extract was sold in the US alone.
Conducted by researchers at Williams College in Williamstown, Massachussetts and The Memory Clinic in Bennington, Vermont, the team selected 230 volunteers over the age of 60 who were physically and mentally healthy. Each participant underwent 14 tests of learning, memory, and attention and concentration, and their companions (eg spouses, partners, close friends) helped to rate their mental functions on subjective scales.
Participants were then randomly divided into two groups: one took gingko and one took a placebo. The study was double-blind; neither the participants nor the researchers knew who was taking ginkgo and who was taking placebo.
The manufacturer of the product claims that beneficial effects would be noticed after four weeks. After six weeks, participants in the study retook the 14 standardised tests and they and their companions re-rated participants' mental functions. There were no significant differences between those taking ginkgo and those taking placebo on any of the objective or subjective measures.
"Many of our patients and their families who are seen at the Memory Clinic in Bennington have asked whether ginkgo could slow or reverse the effects of ageing on memory," said the study's lead author, Dr Paul Solomon, professor of psychology and founding chair of the Williams college's Neuroscience Program.
"Since there were no scientifically rigorous studies of this, we decided to conduct a study of ginkgo on memory. The results indicate that when taken following the manufacturer's instructions, ginkgo provides no measurable benefit in memory, attention, or concentration in healthy older adults. We hope others will now further test ginkgo and other vitamins and nutrients to see if they really provide the benefits they claim.
"As with any over-the-counter substance, people taking ginkgo, or thinking of taking it, have to decide for themselves what's right but they owe it to themselves to inform that decision with knowledge of scientific studies. They also need to consider cost and possible side effects, especially if taken with medication or other substances," added Solomon.
Other researchers welcomed the study. "It is critically important that claims of effectiveness of all treatments, including natural products, be supported by scientifically valid results from well controlled clinical trials," said Dr Steven Ferris, Friedman Professor for Alzheimer's Disease at NYU School of Medicine and executive director of the Silberstein Institute for Aging and Dementia.
"This important, very well conducted clinical trial clearly calls into question previously unsubstantiated claims that ginkgo biloba improves mental function in older people."
Others however did not see the study in the same light. The Council for Responsible Nutrition (CRN), a US trade body which represents ingredient suppliers and manufacturers, urged consumers to judge the results in the context of "the very large body of clinical evidence" on gingko biloba.
"This study should not be viewed as the definitive word on the subject, but simply one more addition to an extensive amount of scientific information, much of it positive, on ginkgo," said Dr John Cardellina, vice president of botanical science and regulatory affairs for the CRN.
The CRN suggested that ginkgo is one of the most clinically studied of all the botanicals in the marketplace, with more than 120 studies carried out to date, and most showing significant, demonstrable benefit. The organisation cited a new report An Expert Review of the Safety and Benefits of Botanicals, to be released in the autumn along with the American Botanical Council (ABC), which evaluates clinical evidence on gingko and finds "clear evidence of benefit from ginkgo for memory and cognitive function in adults with early stage mental impairment and in cases of peripheral vascular disease (intermittent claudication)."
However CRN admitted that the evidence for benefit in cognitive function and memory in unimpaired adult populations is mixed, with some trials showing benefit and others, like this latest study, showing none.
According to Dr Jerry Cott, a psychopharmacologist and a member of the expert panel involved in the report: "This is clearly an area that would benefit from additional, carefully designed research. As new studies are developed, three factors should be strongly considered in the study design: first, the size of the population to be studied, so that results have statistical significance for the effects to be measured.
"For example, a study of normal elderly is really a population study requiring many thousands of subjects over several years, whereas a study of mild cognitive impairment could be accomplished with a more reasonable number of subjects in a shorter period of time. The second factor is the specific effects to be measured and the means to measure them accurately, and the third is the dose or dose range to be investigated to achieve the sought-after effects."
California-based supplement maker Pharmavite also issued a response to the study, backing claims for the benefits of its Nature's Resource and Nature's Made brand gingko biloba.
Dr Steven Yannicelli, Pharmavite director of Continuing Education, said that the study should be evaluated in the context of other studies that document the herb's benefits for healthy people.
"If people are taking ginkgo and finding it helpful, this one study's findings should not deter their continued use of this herb," said Yannicelli.
The industry is clearly worried about the effects of the study however. Statements were also issued by the American Botanical Council, the American Herbal Products Association and the National Nutritional Foods Association, all urging consumers to consider the study in a wider context of available evidence supporting the benefits of gingko biloba.