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.© Food Safety News