A recent toxicology report prepared by the U.S. National Toxicology Program (NTP) on a Ginkgo biloba extract, which was based on a series of mice and rat studies, indicated that supplementing these animals' diets with this particular Ginkgo extract caused liver and thyroid tumors. The NTP report is flawed in two significant ways.
The first flaw is that the researchers employed unusually large doses of a specific Ginkgo extract for as long as two years and at doses dramatically larger than those that would be recommended for humans. The dosages used in the study ranged from a low of 62.5 mg per kg of body weight, to a high of 2,000 mg per kg of body weight. These animal dosages translate to a human dose – for a 155-pound individual – of 4.4 grams per day at the low range, which is 29 times the dose Thorne Research recommends, to 140 grams per day at the high range, which is 933 times the dose Thorne Research recommends. Given that Ginkgo is a botanical extract with proven bioactivity, the doses reported by the NTP are unreasonable and unwarranted. It is arguably self-evident that any botanical extract, overdosed for two years, would cause adverse effects in an animal.
The second flaw pertains to the specific Ginkgo extract used in the NTP study. Although the NTP researchers stated the extract employed in the study was, "procured from a supplier known to provide material to United States companies," the extract was, in fact, not an extract representative of the concentration and purity commonly used in the United States. Rather than the typical concentrations up to 24% Ginkgo flavone glycosides and 6% terpene lactones, the material used in the study, which was provided by a Chinese manufacturer, contained 31% Ginkgo flavone glycosides and 15% Ginkgo terpene lactones. Nor was the Chinese extract analyzed for all potential contaminants. The source of the Ginkgo analyzed in the NTP study and its atypical potency is outside of the norm, further exacerbating the massive dosages used in the study. It is therefore very probable that the excess Ginkgo flavone glycosides and terpene lactones acted as a multiplier for the potency of the dosage used.
With the use in this study of enormous doses of a non-standard Ginkgo extract, it is extremely risky to attempt to extrapolate this information to any useful recommendations related to human toxicity, which was, appreciably, noted by the NTP study's authors. According to Mark Blumenthal, the executive director of the American Botanical Council, "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."
It is highly important to note that Ginkgo has been used for centuries throughout the world, and prior to this report its safety has never been called into question. After careful review and analysis of the NTP study, Thorne Research has concluded that, given its methodological flaws, the NTP study should not be the deciding factor in determining the safety of Ginkgo and whether or not one should use a Ginkgo-containing supplement.
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