Ginkgo biloba, the popular dietary supplement purported to have memory-enhancing properties, has been linked to cancer in rats and mice, according to a new government study. After administering ginkgo regularly to rodents over a two-year period, researchers at the National Toxicology Program (NTP) found that the animals were more likely to develop thyroid and liver tumors than those who did not receive the plant extract, or who received low doses. In a shorter three-month trial, rats and mice who were administered ginkgo displayed characteristics that predict tumor growth. “The tumors found in mice were pretty impressive,” said Dr. Cynthia Rider, NTP’s study scientist for ginkgo. “They were among the highest in NTP studies for one of the tumors that doesn’t occur simultaneously all the time in mice,” Rider explained in an interview with Food Safety News. The mice in the three-month study were put into six dosage groups – no ginkgo, 125 mg per kg of body weight, 250 mg/kg, 500 mg/kg, 1,000 mg/kg and 2,000 mg/kg. Doses were administered five times a week. After three months, all mice who had received 250 mg/kg or more had heavier livers than those who had received no extract. Over the course of the two-year study, cancerous tumors developed in all dosed male mice and in female mice who had been given 600 mg/kg or higher. Only some rats in the two-year study developed liver tumors, but higher levels of thyroid tumors were noted among these rodents. How do these results translate into advice for consumers? What dose of ginkgo extract could put a person at risk for cancer, or does the extract cause a risk to humans at all? To answer these questions, more research is required, said Rider. “I think it’s better to leave that part of the interpretation from our perspective and just say that considering the findings, which were positive for carcinogenisis in both the male and female rats and mice, that they may be related.” “Because these supplements are incredibly complex because they’re based on plant materials, we did not do the full toxicokinetic studies that would be needed to make the comparison,” Rider explained. Toxicokinetics is a way of tracking what happens to a substance in the body. So far, another research team at NTP has conducted an analysis of the liver tumors that developed in the mice. The results of that study showed that the liver tumors that grew in mice given ginkgo extract were different from those that arise spontaneously in mice. Researchers reported a “marked differences between these tumors and those arising spontaneously in the B6C3F1 mouse.” What Rider can say about her team’s results is that they show a potential connection between ginkgo and cancer, and that the substance should be looked at to see whether it indeed provides more benefit than potential risk. She points to a 2008 study on the potential effects of ginkgo on memory, for which over 3,000 participants were given either ginkgo extract or a placebo and followed for an average of 6 years, and no difference in memory function was observed between the groups. “If you’re doing your own personal risk-benefit calculation, you might want to consider the human efficacy studies and our studies as well as the variability seen in the marketplace,” said Rider. The American Botanical Council questioned the results of the government research, saying that the ginkgo used in the NTP study did not reflect extracts commonly found in the U.S. “The Chinese ginkgo extract manufactured in Shanghai is not consistent with any compendial botanical and chemical standards for quality as set forth in various official pharmacopeias and does not conform to the well-established chemical profiles, quality, and purity of the leading, clinically tested ginkgo extracts produced by the pioneering Willmar Schwabe Pharmaceuticals of Karlsruhe, Germany, and Indena SpA in Milan, Italy,” said ABC in a statement last week.  However, according to Rider, “The Ginkgo biloba extract used in the current studies was procured from a supplier known to provide material to United States companies.” Rider said she and her colleagues found a wide variety of compositions among ginkgo supplements sold in the U.S. This may be due to the fact that ginkgo, as a dietary supplement, is not regulated by the U.S. Food and Drug Administration. With the passing of the Dietary Supplement Health and Education Act of 1994, the responsibility of ensuring the safety of dietary supplements was transferred from FDA to manufacturers. “Dietary supplements do not need approval from FDA before they are marketed,” says FDA on its website. “A firm does not have to provide FDA with the evidence it relies on to substantiate safety or effectiveness before or after it markets its products,” continues the agency’s Q & A page on dietary supplements. In 1997, a Denver-based company petitioned FDA to include ginkgo biloba in its list of ingredients that are “generally recognized as safe,” or GRAS, and are therefore allowed to be used as food additives. But the company withdrew its request in 2000, and ginkgo has still not been approved for use in foods.

  • 125 mg/kg is a very high dose. Most human supplements are at a recommended dose of anywhere from 60-120 mg total once or twice daily for an average size human. The equivalent used in the lowest dose in the study would equate to a human taking over 18 GRAMS of ginkgo daily.

  • Trudy Lamb

    Sounds like junk science. First off, you can’t “research” a natural dietary substance as you would a synthetic pharmaceutical drug–FDA requires 1,000 times a normal serving per day. Even water would kill you–1,000 servings–8,000 ounces–62 gallons a day!

    Massive amounts of anything can cause cancer. Research design ignores that the body routinely kills cancer cells on a daily basis. Only when the body’s systems are pushed beyond their normal limits does the body become overwhelmed to the point that it cannot keep up–and cancer ensues. Too much of anything overloads the body’s functioning–thus breakdowns in thyroid, liver, etc..

    Anything can be “scientifically” shown to be detrimental, in sufficient quantity.

    This fact of nature alone throws research designs and findings into the trash–where they belong.

    More proof of junk science: The conclusions exceed the findings. The gingko study reminds me of a 1930s study in my 6th grade-school (1950s) textbook. The finding: Massive amounts of lipstick force-fed to rats
    resulted in cancer. The conclusion: No one should ever wear any lipstick at all. WHY: Trace amounts of
    lipstick on lips MIGHT be ingested, which MIGHT
    result in cancer!

    The real WHY: A growing trend of “painted lips” in teen girls. So the Old Guard discredited lipstick. Any way they could.

    Lipstick then, gingko now.

    Both studies deserve “cult-movie” status–at least as thrilling as “Attack of the Killer Tomatoes.”

  • Jacquelyn Brown

    This is laughable! If you read the study, the ginko was administered mixed with corn oil. But it couldn’t be the corn oil. Oh no. That is not even mentioned. Talk about an Omega-6 overload. AND what Trudy Lamb said below.

  • Maidenhair

    This study had highly questionable aspects. Firstly, the extract used did not appear to conform to the usual standards seen in German Comission E, i.e. EGB761, an extract that has been shown non-toxic in pregnant rabbits, rats and mice (it had no effect whatsoever) at extremely high doses – as high as those seen in this study (i.e. over 1000 mg/kg, a ridiculously high dose).

    The extract had 31/15% of flavonoids and terpene lactones, respectively, rather than 24/6% respectively. That means less organic acids, proanthocyanidins, catechins and all the other stuff that makes up EGB761. Heavy metals were OK, Ginkgolic acid was not particularly high but still three times the amount you would get from EGB761. At higher concentrations Ginkgolic acid can be a toxic agent.

    We’ve seen this before. A study showing that EGB761 caused DNA mutations in rat testes contradicted previous studies which showed the exact opposite. It subsequently turned out not to have been EGB761 at all but rather some dodgy extract from Egypt that did not meet basic standards for ginkgolic acids and heavy metals.

    The extract used in this study may not be that bad but it certainly does not look like a high quality product that meets the normal standards for Ginkgo Biloba extracts used in experimental analyses.

    Secondly, the doses of the extract used were extremely high. The highest dose, 2000 mg/kg, is actually over 10% of the LD50 (dose required to kill 50% of rats) or Ginkgo Biloba which I have seen quoted at about 17000mg/kg dose.

    Given that the extracts are supposed to be equivalent to about 50 times as much pure powdered leaf, this amounts to eating (in nature) 850 grams per kilogram (i.e. eating your own body weight pretty much). That’s… more than I would normally eat!

    In most such things (herbs) the LD50 dose kills by overloading the liver. The LD50 dose for green tea is 4000 mg/kg. For medicines like aspirin it’s 700 mg/kg and for paracetemol it’s 300 mg/kg!

    What this study could be interpreted as saying is that the Ginkgo Biloba extract given (despite being not compliant with the expected standard) was relatively benign. Even at the dose of 2000 mg/kg, a high dose, the mortality rate in female rats was actually *REDUCED*! Why the megadose didn’t effect the females as much as males is unclear.

    Compare this to Aspirin. Ginkgo Biloba, we are to assume, is dangerous because at 2000 mg/kg it (allegedly) causes cancer. Aspirin, meanwhile, is safe, because at 2000 mg/kg it only causes death!

    • marielitis

      My mum was drinking tea prepared with ginkgo biloba leaves everyday for a period of around 3 years. She died of brain cancer that is when glial cells in the brain start degenerating. One of the effects attributed to gingko biloba is the “power” to stimulate glial cells. I totally believe that ginkgo biloba leads directly to cancer!!!!