Skeptical Raptor's Blog hunting pseudoscience in the internet jungle

Ginkgo biloba and the brain–myth vs. science

ginkgo-health-benefits-bullshitGinkgo biloba is actually an interesting plant because it has been relatively unchanged for nearly 270 million years. It is considered a living fossil, an informal term used for species like G. biloba that appear to be the same as a species otherwise only known from fossils and which has no close living relatives. The genus Ginkgo was fairly widely distributed until about 100 million years ago. It slowly disappeared from the fossil record until it was found only in one small part of China about 5 million years ago, where it is found today.  

The tree is native to China and is known to have been widely cultivated early in human history. It is used as a food source by various Asian cultures, with the Chinese eating the meaty gametophytes and the Japanese the whole seed. Unfortunately, the seed also contains a chemical, 4′-O-methylpyridoxine, that can be poisonous if consumed in a sufficiently large enough quantity. 

Myth

Ginkgo biloba has been used for centuries as a medicinal herb, part of Traditional Chinese Medicine, which really is Traditional Chinese, but is not evidence-based medicine. Not even close. One of more popular claims was for Ginkgo was that it was supposed to enhance cognitive functions, something that is pushed by Big Herbal for profits. Part of the justification for this claim was always kind of weak–G. biloba has a mild blood thinning effect. Also the leaves contain glycosides and and terpenoids that may exhibit reversible, non-selective monoamine oxidase inhibition, which could have an effect on neurotransmitters. It was then claimed that the herbal drug would enhance blood flow to the brain and the other chemicals would improve brain and nerve function. Typical pseudoscience, find some kernel of scientific fact, and blow it up well beyond what is supported by real evidence.

Sometime in the last 10-15 years or so, Ginkgo biloba became a popular supplement and a few studies showed promise for a few “indications” for the brain..

  • In 2000, a very small (20 patient) study showed some improvement in attention in healthy volunteers who received Ginkgo supplements.
  • A few studies showed some improvement in cognitive outcomes with Gingko supplements with dementia patients. One moderately sized study showed that when a Gingko extract given as a single 240 mg daily dose, “was found significantly superior to placebo in the treatment of patients with dementia with neuropsychiatric symptoms.”  The study has not been repeated by researchers in other locations (Germany seems to be woo-central for herbal medicines).
  • A meta-analysis of clinical trials seems to have have shown that Ginkgo might be moderately effective in improving cognition in dementia patients. However, the authors (German again) admitted that the was no evidence of clinical relevance or whether there was any benefit to the patient.
  • A small pilot study seems to show “that Ginkgo exerted modest beneficial effects on select functional measures (eg, fatigue) among some individuals with multiple sclerosis.” However, this study was published in a very low impact factor journal that focuses on “natural” treatments. Moreover, the authors bely their bias by reporting the observation that some individuals had some select benefits. Without a statistical measure between the outcomes for all patients in the Ginkgo group versus the control group, there is no evidence that the Ginkgo group exhibited anything but placebo effects.

Of course, these are small studies, and I’ve just picked out the positive studies from the body of evidence on Ginkgo. Of course, a quick search on google will provide you with dozens of hits of supplement hawkers who are more than willing to sell you gingko supplements claiming to help you fix all that ails your brain. 

So, is this more than just a myth? Does is that enough evidence to support buying it? It seems like there’s even a tiny glimmer of evidence supporting Ginkgo’s effects on reducing or even reversing cognitive declines in dementia. It even might help with multiple sclerosis. Except, no, there isn’t.

Science

One of the themes that you might notice from reading this blog is that you can prove almost anything if you cherry pick data or quote mine information. As I’ve discussed before, it’s important to find secondary sources that roll up the broad body of research to answer a question, not just one or two pieces of primary data that makes your case. And what I did above was quickly search out articles that supported the myths about Gingko biloba. But what does the high quality research tell us?

  • As I’ve said before, the Cochrane Reviews are the best place for secondary reviews of clinical research, and in a 2007 meta-review, the authors state that there is no convincing evidence that Ginkgo biloba is efficacious for dementia and cognitive impairment. That’s pretty definitive, especially for Cochrane who can be frustratingly obtuse in their conclusions. The authors state “there is no convincing evidence that Ginkgo biloba is efficacious for dementia and cognitive impairment.”
  • A 2008 randomized clinical trial, which included 3069 older adults with normal cognitive function or mild deficits, G biloba showed no benefit for reducing all-cause dementia or dementia of the Alzheimer type.
  • A 2012 long-term randomized clinical trial of standardized ginkgo biloba extract did not reduce the risk of progression to Alzheimer’s disease compared with placebo. The authors stated that Ginkgo “was not effective in reducing either the overall incidence rate of dementia or Alzheimer’s disease incidence in elderly individuals with normal cognition or those with mild cognitive impairment.” This was a high quality clinical trial published in a high impact factor journal.
  • Finally, a large randomized study with 120 patients, larger than the one mentioned in the section above, concluded that G. biloba did not improve cognitive performance in persons with multiple sclerosis. In other words, when a group decided to repeat the study, they found nothing. 

Conclusion

It’s unclear how Gingko biloba started out in alternative medicine, but apparently it has some minor blood thinning and neurological effects, so it probably had some use for early humans. However, as shown in clinical trials published in the top journals in medicine, it really doesn’t have much of an effect on your brain.

This happens over and over again, find some minor effect, then take leap of faith to some major clinical effect. Well, the major clinical trials and secondary reviews say there is nothing there. Don’t bother with it. As Steven Novella at Neurologica stated recently in a discussion about Gingko, “early positive-biased research with later more rigorous studies finally giving us reliable information, in this case that Gingko is ineffective for the indication for which it is most commonly used.”

There is an important lesson to be learned here. Early trials on things (whether it’s Ginkgo, cannabis, or some random substance) sometimes show a positive benefit. But it’s what’s shown in more rigorous, better designed studies that matter. That’s when you can leap, but not on faith, but on scientific evidence.

In short, don’t bother taking Ginkgo. It doesn’t do anything.

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