The American Herbal Products Association (AHPA), Silver Spring, has disputed the results of a National Toxicology Program (NTP) report on the supposed carcinogenicity of ginkgo (Ginkgo biloba) because the extract used in the study was not chemically similar to products sold for commercial use.
The report, “NTP Technical Report on the Toxicology and Carcinogenesis Studies of Ginkgo biloba Extract in Rats and Mice,” studied the effects of a unique ginkgo leaf extract on rats and mice to identify potential toxic or cancer-related hazards.
However, in comments made during a review of the draft report in February 2012, Steven Dentali, Ph.D., AHPA's chief science officer, presented a data table that compared the NTP gingko extract to published analyses of commercially available ginkgo products and to recognized pharmacopoeial ginkgo standards, highlighting the unique, uncommon identity of the NTP ginkgo extract. Dr. Dentali's recommendations that the final report make clear these differences in chemical composition and amended to include the word “specific” to properly qualify the test material to avoid confusion with ginkgo products sold commercially in the United States were not incorporated by NTP.
“I'm disappointed that NTP did not adopt AHPA's recommendations to properly qualify the extract that was studied and its relevance to consumers and the marketplace,” said Dr. Dentali. “This is in spite of the fact that two of NTP's own peer reviewers agreed with my suggestion to include the data table showing the constituent ratios of the NTP unique test material versus readily available consumer ginkgo products. The assertions and conclusions in the final NTP report are not necessarily relevant to other commercially available ginkgo products."
The American Botanical Council (ABC), Austin, TX, echoed AHPA’s response by reassuring that clinically tested ginkgo extracts sold as dietary supplements in the U.S. are safe for most consumers.
In February 2012, ABC also sent public comments to NTP for the authors of the ginkgo study to consider in revising the draft report. The ABC comments were compiled by a committee of medicinal plant science and toxicology experts. ABC emphasized that 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.
“The ginkgo extract used in this study is different from the high-quality ginkgo extracts used in published clinical trials showing safety and various beneficial activities of ginkgo,” said Mark Blumenthal, founder and executive director of ABC. “That is, the Shanghai ginkgo extract used by NTP does not represent the quality of German ginkgo extract that is the world standard for ginkgo. It is highly unfortunate that NTP chose to use this ginkgo extract as it means that the results of the NTP’s studies are not applicable to the standard-setting ginkgo extracts.”
In addition, ABC noted that the dosage levels administered to the test animals was significantly higher (up to 55-108 times higher) than the levels of ginkgo extract that are normally ingested by consumers (120-240 milligrams per day), as calculated by ABC’s consulting toxicologist. “At best, what NTP can say is that significantly high doses of this particular Shanghai Chinese ginkgo extract—when added to a corn-oil base— produced cancer in the lab animals,” added Mr. Blumenthal.
ABC also emphasized that the NTP studies are not intended to imply potential adverse effect in humans. “The NTP’s public message, and the resulting media reports, totally miss this point about the actual identity of the ginkgo extract and the high-dosage levels, and will probably cause confusion among consumers and health professionals alike,” added Mr. Blumenthal.
“Almost anything will create cancer in rats and mice when it’s fed to them at high doses for two years,” said Bill J. Gurley, PhD, professor of pharmaceutical sciences in the College of Pharmacy at the University of Arkansas School for Medical Sciences, Little Rock. “All toxicologists and pharmacologists are aware of the susceptibility of certain strains of rodents used for research purposes to develop various forms of cancer and other diseases when subjected to various substances.”
“This is disappointing, to say the least,” said Rick Kingston, PharmD, president of regulatory and scientific affairs at SafetyCall International in Minneapolis, MN, and professor of pharmacy at the University of Minnesota College of Pharmacy. “Notwithstanding major design flaws in the study in identifying an appropriate compound to represent available ginkgo in the market,” continued Dr. Kingston, “even the reviewers voiced adamant proclamations that the results in this animal research were not intended for direct extrapolation to humans. For this oversight to not be reconciled by the NTP review group is disconcerting, especially since misinterpretation of the results by well-intentioned, but scientifically unsophisticated media outlets, and possibly even consumer groups, should have been an expected outcome.”
The ABC comments sent to NTP as part of the public comment process also called attention to other anomalies and/or problems with the NTP ginkgo studies as noted in the draft report. These include concerns that the Shanghai ginkgo extract used in the NTP study was from several different production batches, and that the ginkgo extract material used in the study was not analyzed for the presence of potential contaminants.