Skeptical Raptor's Blog hunting pseudoscience in the internet jungle

Ginkgo biloba and neurological disorders–Myth vs. Science

I’m trying out a new series, looking at some popular myths (mostly in medicine, but maybe we’ll wander outside of it when something interesting shows up) and determining if there’s any support or not in science. I’m going to link mostly to science articles and high-quality blogs, just so you have all the back-up evidence that you need. One way or another.

Background

Ginkgo 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 contains a chemical, 4′-O-methylpyridoxine, that can be poisonous if consumed in enough quantity. 

Myth

Gingko biloba has been used for centuries as a medicinal herb, part of Traditional Chinese Medicine, and one of its most popular claims was for its use was to enhance cognitive functions. 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.

Sometime in the last 10-15 years or so, Gingko 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 large 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.”
  • A meta-analysis of clinical trials seems to have have shown that Ginkgo might be moderately effective in improving cognition in dementia patients.
  • 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

 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 is 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.
  • 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.
  • 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. 

What the Skeptical Raptor says

It’s unclear how Gingko biloba started out in alternative medicine, but apparently it has some minor blood thinning and neurological effects. This happens over and over again, find some minor effect, then leap 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.”

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