The dietary supplement Ginko biloba, which some believe helps improve memory (although studies have shown it is ineffective), has been linked to cancer in ratrs and mice. The new study, conducted by scientists at the National Toxicology Program (NTP), found that animals who received the supplement were more likely to develop tumors in the liver and thyroid than animals who were not given the extract.
In the study, scientists gave 50 male and female rats corn oil solutions with 100, 300, or 1,000 milligrams of Gingko biloba extract per kilogram of body weight five times a week for two years. Another group received 200, 600, or 2000 mg/kg every day. Those concentrations fall within the range of what is on the market. The supplier of the extract does supply material to companies in the U.S. Control groups were given solutions of corn oil with no chemical added. At the end of the study, tissues at 40 sites were examined for every animal.
Every group of animals exposed to Gingko biloba extract experienced “increased rates of a variety of lesions in the liver, thyroid gland, and nose, and male and female mice also experienced several different lesions in the forestomach. These lesions included hypertrophy in the liver and thyroid gland in rats and mice, liver hyperplasia in male and female rats, hyperplasia and atrophy of the epithelium within the nose of male and female rats, and inflammation, hyperplasia, hyperkeratosis, and ulcer in the forestomach of male and female mice.”
The researchers concluded that “Gingko biloba extract caused cancers of the thyroid gland in male and female rats and male mike and cancers of the liver in male and female mice.” There was clear evidence of carcinogenic activity of Gingko biloba extract in male B6C3F1/N mice and female B6C3F1/N mice based on increased incidence of hepatocellular carcinoma and hepatoblastoma.
One of the major components in Ginkgo biloba extract, quercetin, is a known mutagen. The NTP would like to see more research looking at the relevance of the Ginkgo biloba extract findings in humans. Dietary supplements do not need approval from the government before they are sold and do not need to prove safety or efficacy before or after the products are marketed thanks to the 1994 Dietary Supplement Health and Education Act.
