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Recent headlines have questioned Gingko biloba's safety, only to be challenged by natural health practitioners who say the remedy is safe and potentially effective for improving a range of conditions, including age-related memory impairment and dementia, eye problems associated with diabetes (diabetic retinopathy), premenstrual syndrome (PMS), vertigo, and glaucoma. Who's right? Putting the latest research into context can help you better understand the big picture on ginkgo.
Of mice and men (and rats)
Researchers conducted toxicology studies of standardized Ginkgo biloba extracts in 100 rats and 100 mice. For two years, the animals were fed corn oil solutions containing varying amounts of Ginkgo biloba, through a tube inserted into the stomach.
The rats received 0, 100, 300, or 1,000 mg of ginkgo extract per kilogram of body weight, administered five days per week. The mice received 0, 200, 600, or 2,000 mg of ginkgo per kilogram of body weight, administered five days per week. At the end of the two-year study, the animals were dissected, and tissues from 40 areas in each animal's body were examined for abnormalities.
The findings, detailed extensively in a 191-page report, note, "We conclude that Ginkgo biloba extract caused cancers of the thyroid gland in male and female rats and male mice and cancers of the liver in male and female mice." This is concerning, but does it mean ginkgo causes cancer in humans?
Getting down to details
While popular media reports suggest Ginkgo biloba is now a proven carcinogen (cancer causing substance) that should be removed from the market, the details paint a more nuanced picture. Before you toss your ginkgo supplements, consider the following:
Note the dose. Recommended human doses for Ginkgo supplements range from 30 to 240 mg per day, regardless of body weight. The study animals received up to 1,100 times this amount--the amount of ginkgo (by body weight) that would be appropriate for an "average," 150-pound person.
Count the years. According to rodent experts, each rat or mouse year is roughly equivalent to 30 human years. In other words, the animals were given massive doses of Ginkgo biloba for nearly their entire lifespans--what would be equivalent to a person taking 500 to 1,000 times the amount of a typical Ginkgo biloba supplement, for 60 years.
Consider history. In the 1970s, rat studies linked saccharin with bladder cancer risk, prompting a warning label on saccharin-containing foods, "saccharin has been determined to cause cancer in laboratory animals." Further study indicated these results were not applicable to humans, and the high doses originally tested weren't representative of typical human use. In 2000, saccharin was removed from the National Toxicology Program's Report on Carcinogens list. While no one would argue that saccharin is "good for you," this episode illustrates how animal toxicology research can lead to erroneous conclusions about human health.
Aim for the middle ground. For every vitamin, mineral, and phytonutrient tested, optimal intake levels are neither too high, nor too low. Consider some examples: Not enough vitamin A can lead to blindness, infections, and even death. Too much vitamin A can lead to osteoporosis, birth defects, liver failure, and death. Getting plenty of folate before and during pregnancy is vital for preventing birth defects, yet too much folate, particularly as folic acid--found in supplements and fortified foods--has been linked with increased risk of some types of cancer. It should come as no surprise that long-term use of excessively high doses of any substance, including Ginkgo biloba, causes measurable adverse health effects.
Consult your health provider. In the end, a single, high-dose toxicology study does not prove Ginkgo biloba causes cancer, particularly for a natural product with a long history of safe use. If you have concerns about ginkgo, or any dietary product you currently use or want to try, talk to your doctor, nurse, or dietitian about this.
(NTP Technical Report on the Toxicology and Carcinogenesis Studies of Ginkgo Biloba Extract in F344/N Rats and B6C3F1/N Mice. March 2013. NIH Publication No. 13-5920. Accessed June 18, 2013: http://ntp.niehs.nih.gov/ntp/htdocs/LT_rpts/TR578_508.pdf)
Suzanne Dixon, MPH, MS, RD, an author, speaker, and internationally recognized expert in chronic disease prevention, epidemiology, and nutrition, has taught medical, nursing, public health, and alternative medicine coursework. She has delivered over 150 invited lectures to health professionals and consumers and is the creator of a nutrition website acclaimed by the New York Times and Time magazine. Suzanne received her training in epidemiology and nutrition at the University of Michigan, School of Public Health at Ann Arbor.
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